rexresearch.com


Sophia YANG, et al.

Metal Microlattice








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Patents

US2013303067
Ventilated Aero-Structures, Aircraft, and Associated Methods

US2014272275
MICRO-TRUSS MATERIALS HAVING IN-PLANE MATERIAL PROPERTY VARIATIONS

WO2014137924
ENERGY ABSORBING TRUSS STRUCTURES FOR MITIGATION OF INJURIES FROM BLASTS AND IMPACTS

US2014252674
ARCHITECTED MATERIALS FOR ENHANCED ENERGY ABSORPTION

US9096722
A METHOD FOR CURING STRUCTURES USING A DUAL PHOTOINITIATOR SYSTEM AND A STRUCTURE MADE USING THE SAME

US2015176132
STRUCTURES HAVING SELECTIVELY METALLIZED REGIONS AND METHODS OF MANUFACTURING THE SAME

US8195023
FUNCTIONALLY-GRADED THREE-DIMENSIONAL ORDERED OPEN-CELLULAR MICROSTRUCTURE AND METHOD OF MAKING SAME

US7382959
OPTICALLY ORIENTED THREE-DIMENSIONAL POLYMER MICROSTRUCTURES

US8353240
Compressible fluid filled micro-truss for energy absorption

WO2015095617
STRUCTURES HAVING SELECTIVELY METALLIZED REGIONS AND METHODS OF MANUFACTURING THE SAME



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Boeing's micro lattice metal

Boeing's micro lattice metal -- Microlattice is the lightest metallic structure ever made. At 99.99% air, it's light enough to balance on top of a dandelion, while its structure makes it strong. Strength and record breaking lightness make it a potential metal for future planes and vehicles. Learn more about Boeing Innovations at http://www.boeing.com/innovation/





 



PATENTS

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US2013303067
Ventilated Aero-Structures, Aircraft, and Associated Methods

Ventilated aero-structures include a micro-lattice structure operatively coupled to a honeycomb core. The interface between the honeycomb core and the micro-lattice structure is configured to permit air flow to and from the honeycomb core via the micro-lattice structure. Aircraft include a ventilated aero-structure and a ventilation system configured to circulate air through the ventilated aero-structure. Some methods include coupling a micro-lattice structure to a honeycomb core. Some methods include utilizing a ventilated aero-structure to assemble an aircraft...

BACKGROUND

[0002] Honeycomb structures are often used in the construction of aircraft, because they typically have high strength to weight ratios. Typically, honeycomb structures are sandwiched and bonded between opposing panels, or face-sheets, resulting in closed volumes of air within the cells of the honeycomb structures. Closed cells are susceptible to collecting moisture and do not permit airflow for venting, cooling, or heating applications. Moisture ingress may contribute to failure of the bond between the honeycomb structure and adjacent panels, as well as separation and degradation of cells of the honeycomb structure. Unvented honeycomb structures may be difficult to process in autoclave bonding operations, which use gas pressure and/or vacuum to apply forces to the structure to achieve bonding, because pressures can build and collapse the honeycomb structure.

SUMMARY

[0003] Ventilated aero-structures according to the present disclosure include a micro-lattice structure and a honeycomb core operatively coupled to at least one side of the micro-lattice structure. The interface between the honeycomb core and the micro-lattice structure is configured to permit air flow to and from the honeycomb core via the micro-lattice structure. Aircraft according to the present disclosure include a ventilated aero-structure and a ventilation system configured to circulate air through the ventilated aero-structure.

[0004] Methods of constructing ventilated aero-structures according to the present disclosure include coupling a micro-lattice structure to a honeycomb core. Methods of assembling aircraft according to the present disclosure include utilizing a ventilated aero-structure to define a portion of the aircraft's airframe...

BRIEF DESCRIPTION OF THE DRAWINGS

[ PDF ]

[0005] FIG. 1 is an isometric view of an aircraft.

[0006] FIG. 2 is a schematic diagram representing ventilated aero-structures according to the present disclosure.

[0007] FIG. 3 is a schematic plan view representing an illustrative, non-exclusive example of a ventilated aero-structure that includes a series of spaced-apart projections.

[0008] FIG. 4 is an isometric view of a portion of an illustrative, non-exclusive example of an aero-structure according to the present disclosure.

[0009] FIG. 5 is an isometric view of a micro-lattice structure with an adherence grid.

[0010] FIG. 6 is a schematic plan view illustrating an interface between an adherence grid and a honeycomb core structure.

[0011] FIG. 7 is a schematic side view illustrating an interface between an adherence grid and a honeycomb core structure.

[0012] FIG. 8 is a schematic cross-sectional side view representing illustrative, non-exclusive examples of aero-structures according to the present disclosure that define a leading edge of an airfoil.

[0013] FIG. 9 is another schematic cross-section side view representing illustrative, non-exclusive examples of aero-structures according to the present disclosure that define a leading edge of an airfoil.

[0014] FIG. 10 is a flow-chart schematically representing illustrative non-exclusive examples of methods according to the present disclosure.

[0015] FIG. 11 is a schematic plan view representing illustrative non-exclusive examples of masks that may be used to form an adherence structure on a micro-lattice structure.

[0016] FIG. 12 is another schematic plan view representing illustrative non-exclusive examples of masks that may be used to form an adherence structure on a micro-lattice structure.

[0017] FIG. 13 is a schematic side view representing a curing step of methods according to the present disclosure.

[0018] FIG. 14 is a schematic side view representing illustrative, non-exclusive examples of molds that may be used to form an adherence structure on a micro-lattice structure.



US2014272275
MICRO-TRUSS MATERIALS HAVING IN-PLANE MATERIAL PROPERTY VARIATIONS

A micro-truss sheet having material properties varying across the sheet. The sheet may include a plurality of truss members intersecting at nodes. The diameter of the truss members at one point in the sheet may differ from the diameter of the truss members at another point in the sheet. In one embodiment the spacing between adjacent truss members may be different in one part of the sheet from the spacing between adjacent truss members in another part of the sheet.

CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application incorporates by reference in its entirety, as if set forth in full, U.S. Pat. No. 8,195,023 (“the '023 patent”), entitled “FUNCTIONALLY-GRADED THREE-DIMENSIONAL ORDERED OPEN-CELLULAR MICROSTRUCTURE AND METHOD OF MAKING SAME”, and U.S. Pat. No. 7,382,959 (“the '959 patent”), entitled “OPTICALLY ORIENTED THREE-DIMENSIONAL POLYMER MICROSTRUCTURES”.

FIELD

[0002] The present invention relates to micro-truss materials, and more particularly to micro-truss materials in sheet form, with material properties varying across the sheet.

BACKGROUND

[0003] Polymer cellular materials or three-dimensional (3D) microstructures, having the shape of a three-dimensional micro-truss, have numerous applications, including applications as mechanical structures for support, cushioning, and shock-absorption, as heat or mass exchangers or components thereof, and as flow-regulating devices or materials.

[0004] In these applications it may be desirable that the properties of a piece of material not be uniform throughout the piece, but varying. For example, in a flow control material, it may be preferred to have a greater rate of flow through one portion of the piece of material than another, or, in a piece of material used as a cushion, it may be preferred that one portion of the cushion be firmer than another portion.

[0005] Thus, there is a need for a micro-truss material with non-uniform properties.

SUMMARY

[0006] The present invention relates to a micro-truss sheet having material properties that vary across the sheet. The diameter of the truss members, or their spacing, for example, may vary across the sheet, providing a novel material suited to applications in which a non-uniform sheet is preferred.

[0007] According to an embodiment of the present invention, there is provided a micro-truss sheet, including: a plurality of first truss members defined by a plurality of first self-propagating polymer waveguides and extending along a first direction; a plurality of second truss members defined by a plurality of second self-propagating polymer waveguides and extending along a second direction; and a plurality of third truss members defined by a plurality of third self-propagating polymer waveguides and extending along a third direction; the plurality of first truss members, the plurality of second truss members, and the plurality of third truss members being integrally provided as one continuous body; the sheet having a length substantially greater than its thickness, and the sheet having a first point and a second point separated along the length of the sheet. Here the diameter of a truss member of the plurality of first truss members, the plurality of second truss members, and the plurality of third truss members at the first point is at least 10% greater than the diameter of a truss member of the plurality of first truss members, the plurality of second truss members, and the plurality of third truss members at the second point...

BRIEF DESCRIPTION OF THE DRAWINGS
[ PDF ]

[0027] These and other features and advantages of the present invention will become appreciated as the same become better understood with reference to the specification, claims and appended drawings wherein:

[0028] FIG. 1A is a perspective view of a micro-truss structure forming a part of a micro-truss sheet according to an embodiment of the present invention;

[0029] FIG. 1B is a perspective view of a unit cell of a micro-truss sheet according to an embodiment of the present invention;

[0030] FIG. 2A is a top-view photograph of a micro-truss sheet having non-uniform properties across the sheet according to an embodiment of the present invention;

[0031] FIG. 2B is a close-up photograph of a portion of the sheet of FIG. 2A;

[0032] FIG. 2C is a close-up photograph of another portion of the sheet of FIG. 2A;

[0033] FIG. 2D is a close-up photograph of another portion of the sheet of FIG. 2A;

[0034] FIG. 3 is a top-view photograph of a non-rectangular sheet having non-uniform properties across the sheet according to an embodiment of the present invention;

[0035] FIG. 4 is a flowchart illustrating a process for forming a micro-truss sheet having non-uniform properties across the sheet according to an embodiment of the present invention; and

[0036] FIG. 5 is a schematic side view of a micro-truss sheet having non-uniform properties across the sheet according to another embodiment of the present invention.



WO2014137924
ENERGY ABSORBING TRUSS STRUCTURES FOR MITIGATION OF INJURIES FROM BLASTS AND IMPACTS


STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0001] This invention was made with U.S. Government support under Contract No. W91CRB-11-C-0112 awarded by the Defense Advanced Research Projects Agency (DARPA) Defense Sciences Office. The U.S. Government has certain rights to this invention.

CROSS-REFERENCE TO RELATED APPLICATION

[0002] The use of metallic lattice (truss) materials for energy absorbing applications is discussed in U.S. Patent No. 7,382,959 ("Optically oriented three-dimensional polymer microstructures"), U.S. Patent No. 8,353,240 ("Compressible fluid filled micro-truss for energy absorption"), and U.S. Patent Application Nos. 11/801,908, filed on May 10, 2007; 12/008,479, filed on January 11, 2008; 12/074,727, filed on March 5, 2008; 12/075,033, filed on March 6, 2008; and 12/455,449, filed on June 1, 2009, which are incorporated by reference herein in their entirety. Various micro-truss structures and methods of manufacturing micro-truss structures are described, for example, in U.S. Patent Application No. 12/455,449, which discloses a method of fabricating micro-truss structures having a fixed area, U.S. Patent Application No. 12/835,276, which discloses a method of continuously fabricating micro-truss structures according to a continuous process (e.g., a strip of arbitrary length), and U.S. Patent No. 8,353,240, which discloses a compressible fluid filled micro-truss for energy absorption. Each of the above cross-referenced applications is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

[0003] The following description relates to energy-absorption materials and more particularly to cellular materials with periodic, ordered micro-micro-truss structures with enhanced energy absorption capabilities for mitigation of injuries from blasts and impacts.

BACKGROUND

[0004] Energy absorption materials are widely used to protect people and goods from damaging impacts and forces. In an impact or blast event these materials should reduce the impulsive load to a level below a damage threshold by absorbing a maximum of energy while not transmitting a stress in excess of the damage threshold. Examples from the automotive, sporting and defense sectors include crash absorbers, helmet pads and blast-mitigating foot pads. Depending on the application, different performance characteristics are required of the energy absorbing material. The injury criterion or damage threshold athdetermines the maximum allowable stress, atr, transmitted through the energy absorber, i.e., to avoid damage is it necessary that atr< σ^. For energy absorbers in direct contact with the human body the injury criterion is generally on the order of 1 MPa.

[0005] Cellular materials are often used as energy absorption materials because they can absorb energy on compression. Single use energy absorption materials may be metallic and include closed or open cell foams and pre-crushed honeycombs; multi-use materials with reversible energy absorption are typically polymeric and include visco-elastic closed or open cell foams, and thermoplastic polyurethane (TPU) twin hemispheres. Lattice structures can be composed of polymer or metallic materials and may consist of a periodic arrangement of solid or hollow members (struts, trusses).

[0006] Figure 1 is a schematic plot illustrating the ideal behavior of an energy absorption material. At low stress, the strain increases linearly with stress, up to a stress of, e.g., 1 MPa. At this threshold stress, the strain of the material increases rapidly at substantially constant stress, and the material absorbs energy. Finally, when the material reaches a high strain referred to as the densification strain, the stress again increases. The maximum possible volumetric energy absorption for a given material structure is calculated as the product of the peak stress with 100% strain.

[0007J Real materials typically deviate from the ideal response and have lower absorption efficiency. Figure 2 illustrates the typical behavior of a lattice or truss structure with high structural symmetry and internal connectivity. Here, after reaching a peak initial stress (labeled as Max. transmitted stress in Figure 2), the strain increases at a lower level of stress, resulting in a reduction in energy absorption compared to the ideal case illustrated in Figure 1. This is believed to be due to the fact that the onset of buckling at a single point in such a structure with high structural symmetry and internal connectivity triggers buckling throughout the structure, which leads to an abrupt loss of load-carrying capability and reduced impact energy absorption efficiency. In such a case, the densification strain is defined as the strain at which the stress- strain curve intersects a horizontal line at the peak initial stress value. The volumetric energy absorbed is calculated as the area under the stress-strain curve between 0% strain and the densification strain. The energy absorption efficiency of such a material is calculated as the ratio of the volumetric energy absorbed to the maximum possible volumetric energy absorption.

[0008] Figure 3 shows a compressive stress-strain response typical of types of aluminum foam used as energy absorption materials. Such materials have a plateau-like stress-strain curve and do not exhibit the non-ideal behavior of an initial stress peak followed by softening. However, such materials have a low densification strain since the stress starts to rise at an increasing rate at approximately 30% strain, which limits the energy absorption efficiency to be about 35%. Figure 4 shows the compressive stress-strain response of an aluminum honeycomb energy absorption material. In this case, the material exhibits a large initial stress peak followed by softening, which limits its energy absorption efficiency to about 34%. Figure 5 shows the compressive stress-strain response of a twin hemisphere energy absorption material. The material exhibits softening after an initial stress peak, which limits its energy absorption efficiency to about 47%. [0009] Certain materials with a truss or lattice architecture have constant architectural parameters through the thickness direction, i.e., the energy absorbing direction of the truss or lattice structure. In these materials, the high structural symmetry and lack of disconnected internal members lead to simultaneous buckling and a sharp loss of load transfer capability as shown in Figure 2. This reduces the energy absorption efficiency of the material as the stress level associated with compaction drops well below the peak value. Figure 6 displays the compressive stress-strain response of a typical hollow metallic micro-truss structure with no enhancement on the structure. It exhibits a large stress peak followed by softening, and additional stress peaks. The energy absorption efficiency is about 15% - 30%.

[0010] Therefore, there is a need for micro-truss or lattice architectures with the inherent structural and low mass benefits of such architectures, yet with improved energy absorption response.

SUMMARY

[0011] Aspects of embodiments of the present invention pertain to architected materials with superior energy absorption properties when loaded in compression. In several embodiments such materials are formed from micro-truss structures composed of interpenetrating tubes in a volume between a first surface and a second surface. The stress-strain response of these structures, for compressive loads applied to the two surfaces, is tailored by arranging for some but not all of the tubes to extend to both surfaces, adjusting the number of layers of repeated unit cells in the structure, arranging for the nodes to be offset from alignment along lines normal to the surfaces, or including multiple interlocking micro-truss structures.

[0012] According to an embodiment of the present invention there is provided a system for protection from impulsive loads as generated by impacts and explosions, the system including: a first micro-truss architecture, wherein the micro-truss architecture is configured to have greater than 50% volume decrease while transmitting nearly constant pressure in the range of 0.3 - 7 MPa under dynamic loading at 1 - 20 m/s impact velocity. [0013] In one embodiment, the first micro-truss architecture includes: a first surface and a second surface parallel to each other with a distance therebetween defining a thickness of the micro-truss architecture; a plurality of angled struts extending along a plurality of non-vertical directions each having a first end on the first surface and a second end; a plurality of nodes where the plurality of angled struts extending along a plurality of directions interpenetrate one another; the plurality of angled struts and the plurality of nodes defining a plurality of unit cells each having an upper node among the plurality of nodes, a lower node among the plurality of nodes, and a cell height, the cell height being the distance between the upper node and the lower node, wherein the second end of each angled struts is on the lower node closest to the second surface at a distance away from the second surface; and a vertical post extending from the first surface in a normal direction having a first end on the first surface and a second end extending past the lower node closest to the second surface onto the second surface...

BRIEF DESCRIPTION OF THE DRAWINGS
[ PDF ]

[0038] Figure 1 is a schematic illustration of the compressive stress-strain behavior of an ideal energy absorption material.

[0039] Figure 2 is a schematic illustration of the compressive stress-strain behavior of a lattice or truss structure with high structural symmetry and internal connectivity and defines the terms used. [0040] Figure 3 shows the quasi-static stress-strain performance of a commercial aluminum foam used as energy absorption material.

[0041] Figure 4 shows the compressive stress-strain performance of a commercial honeycomb material used as energy absorption material.

[0042] Figure 5 shows the compressive stress-strain performance of a commercial polyure hane twin hemisphere material blast protection mat.

[0043] Figure 6 shows the compressive stress-strain performance of a hollow metallic micro-truss material without enhanced structure.

[0044] Figure 7a is a perspective view photograph of a hollow nickel micro-truss with vertical posts that extend past the lower node, according to an embodiment of the present invention.

[0045] Figure 7b is a side view photograph of a hollow nickel micro-truss with vertical posts that extend past the lower node, according to an embodiment of the present invention.

[0046] Figure 8a is a photograph of, and quasi-static test results of, an embodiment of the micro-truss architecture shown in Figures 7a and 7b.

[0047] Figure 8b is a photograph of, and quasi-static test results of, a commercial energy absorption material with a twin hemisphere structure.

[0048] Figure 8c shows an exemplary embodiment of two structures stacked according to an embodiment of the present invention, and the resulting stress-strain response.

[0049] Figure 9a is a side view photograph of an exemplary 1.5-cell tall hollow micro-truss with vertical posts extending only across 1 cell according to an embodiment of the present invention.

[0050] Figure 9b is a top view photograph of an exemplary 1.5-cell tall hollow micro-truss with vertical posts extending only across 1 cell according to an embodiment of the present invention.

[0051] Figure 10 shows the stress-strain curve measured in compression on the structure shown in Figures 9a and 9b. [0052] Figure 11a is a perspective view photograph of an exemplary standard electroless nickel octahedral hollow micro-truss about 5 unit cells tall according to an embodiment of the present invention.

[0053] Figure l ib is a perspective view photograph of an exemplary standard poly(p- xylylene) polymer octahedral hollow micro-truss about 5 unit cells tall according to an embodiment of the present invention.

[0054] Figure 11c is a close-up perspective view photograph pictures of the poly(p- xylylene) polymer octahedral hollow micro-truss of Figure 1 lb.

[0055] Figure 12 shows the stress-strain curve measured in compression on the poly(p- xylylene) structure shown in Figures 1 lb and 11c.

[0056] Figure 13a shows an assembled view and an exploded view of a micro-truss architecture with repeating periodic interlocking unit cell structures according to an embodiment of the present invention.

[0057] Figure 13b shows the simulated stress-strain response, for dynamic compression at 1 m/s, of the embodiment of Figure 13 a.

[0058] Figure 14a shows an assembled view and an exploded view of a micro-truss architecture with interlocked unit cell structures according to an embodiment of the present invention.

[0059] Figure 14b shows the simulated stress-strain response, for dynamic compression at 1 m/s, of the embodiment of Figure 13 a.

[0060] Figure 15a shows a micro-truss based energy absorber combined with a flexible face sheet before a blast event.

[0061] Figure 15b shows a micro-truss based energy absorber combined with a flexible face sheet during a blast event.

[0062] Figure 16 shows a micro-truss based energy absorber combined with an armor plate according to an embodiment of the present invention. {0063] Figure 17 is a schematic drawing of micro-truss based body armor that incorporates air flow cooling through the open-celled structure according to an embodiment of the present invention.

[0064] Figure 18 is a schematic cross-sectional drawing of an exemplary micro-truss structure according to an embodiment of the present invention.

[0065] Figure 19a is a top view illustration of a micro-truss structure with all nodes in an upper layer shifted by 0.1L in same directions according to an embodiment of the present invention.

[0066] Figure 19b is a side view illustration of a micro-truss structure with all nodes in an upper layer shifted according to an embodiment of the present invention.

[0067] Figure 20a is a top view illustration of a micro -truss structure with nodes in a bottom layer shifted according to an embodiment of the present invention.

[0068] Figure 20b is a side view illustration of a micro-truss structure with nodes in a bottom layer shifted according to an embodiment of the present invention.

[0069] Figure 21a is top view of a micro-truss structure with three-fold symmetry where all nodes in one plane sit in the center between the nodes in the planes above and below, according to an embodiment of the present invention.

[0070] Figure 21b is perspective view of a micro-truss structure with three-fold symmetry where all nodes in one plane sit in the center between the nodes in the planes above and below, according to an embodiment of the present invention.

[0071] Figure 22 shows the simulated stress-strain response of the micro-truss structure shown in Figure 19a and Figure 19b.

[0072] Figure 23 is a flow chart describing an exemplary method to fabricate the micro- truss structure according to an embodiment of the present invention.



US2014252674
ARCHITECTED MATERIALS FOR ENHANCED ENERGY ABSORPTION

A three-dimensional lattice architecture with a thickness hierarchy includes a first surface and a second surface separated from each other with a distance therebetween defining a thickness of the three-dimensional lattice architecture; a plurality of angled struts extending along a plurality of directions between the first surface and the second surface; a plurality of nodes connecting the plurality of angled struts with one another forming a plurality of unit cells. At least a portion of the plurality of angled struts are internally terminated along the thickness direction of the lattice structure and providing a plurality of internal degrees of freedom towards the first or second surface of the lattice architecture.

CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application claims priority to and the benefit of U.S. Provisional Application No. 61/775,330, filed on Mar. 8, 2013, entitled ARCHITECTED MATERIALS WITH THICKNESS HIERARCHY, the content of which is incorporated herein in its entirety by reference.

[0002] The use of metallic lattice (truss) materials for energy absorbing application is discussed in U.S. Pat. No. 7,382,959 (“Optically oriented three-dimensional polymer microstructures”) and U.S. patent application Ser. No. 11/801,908 filed on May 10, 2007; Ser. No. 12/008,479 filed on Jan. 11, 2008; Ser. No. 12/074,727 filed on Mar. 5, 2008; Ser. No. 12/075,033 filed on Mar. 6, 2008; Ser. No. 12/455,449 filed on Jun. 1, 2009; and Ser. No. 12/928,947 filed on Dec. 22, 2010. Various micro-truss structures and methods of manufacturing micro-truss structures are described, in U.S. patent application Ser. No. 12/455,449, which discloses a method of fabricating micro-truss structures having a fixed area, U.S. patent application Ser. No. 12/835,276, which discloses a method of continuously fabricating micro-truss structures according to a continuous process (e.g., a strip of arbitrary length), and U.S. patent application Ser. No. 12/928,947, which discloses a compressible fluid filled micro-truss for energy absorption. Each of the above cross-referenced patents and applications is commonly owned by the assignee of the present application and incorporated by reference herein in their entireties.

FIELD OF THE INVENTION

[0003] The following description relates to energy-absorption materials and more particularly to architectured lattice materials with enhanced energy absorption capabilities.

BACKGROUND

[0004] Energy absorption materials have been widely used to protect people and goods from damaging impacts and forces. Energy absorption materials can be divided into two categories: those without truss architecture, and those with truss architecture. The former category includes cellular materials such as metallic or polymeric closed or open cell foams, crushed honeycombs, or other commercial materials such as Skydex™. The latter category includes micro-truss structures composed of solid or hollow members (struts, trusses, or lattices) with constant architectural parameters such as unit cell size, radius, length, or angles of each member, through the thickness direction of the structure. For the former category, the cellular materials dissipate kinetic energy associated with impact via elastic and/or inelastic deformation. The compression response of foam and pre-crushed honeycomb materials approaches an ideal response (as shown in FIG. 1, which will be described in more detail afterwards), but the ability of these materials is limited either by the low densification strain in foams or the low load-bearing capability in pre-crushed honeycombs. In either case, although the response characteristics are ideal, the performance of the material suffers due to non-ideal spatial arrangement of the microstructures.

[0005] Previous materials with truss or lattice architecture have constant architectural parameters through the thickness direction, i.e., the energy absorbing direction of the truss or lattice structure. The high structural symmetry and lack of disconnected internal members lead to simultaneous buckling and a sharp loss of load transfer capability as shown in FIG. 2. This reduces the energy absorption efficiency of the material as the stress level associated with compaction drops well below the peak value.

[0006] Turning now to the behavior of a given energy absorption material during impact or compression, architected materials composed of truss- or beam-like elements experience collapse mechanisms in which the incoming energy or external work is absorbed in three stages: initial buckling, compaction at a constant or near-constant stress plateau, and ultimately full densification. FIG. 1 is a schematic plot illustrating the ideal behavior of an energy absorption material. The initial response of the material is a compressive strain that changes linearly with the compressive stress corresponding to the material response prior to the onset of buckling or plasticity. After reaching a peak stress 101, the ideal material response switches from the linear elastic stage to a constant stress plateau stage 102, where the force transmitted through the material remains uniform and constant, until the material reaches a densification stage in which the strain increases rapidly, linearly or non-linearly, with the stress again. The strain corresponding to the transition point from the plateau stress to the densification stage is identified as the densification strain 103. The maximum possible volumetric energy absorption for a given material is calculated as the product of the peak stress 101 with 100% strain. However, actual architected materials will have deviation from the ideal response and lead to a loss of absorption efficiency. FIG. 2 illustrates the typical behavior of a lattice or truss structure with high structural symmetry and internal connectivity. Here, after reaching a peak stress 201 at the onset of buckling, rather than staying at the peak stress level, the compressive stress drops to a lower plateau stress 202. This is believed to be due to the fact that the onset of buckling at a single point in a structure with high structural symmetry and internal connectivity will trigger buckling throughout the structure, which leads to an instantaneous loss of load-carrying capability and reduced energy absorption efficiency. In such a case, the densification strain 203 is defined as the strain level corresponding to the interception of a horizontal line at the peak stress value with the stress-strain curve. The actual volumetric energy absorbed is calculated as the area under the stress-strain curve between 0% strain and the densification strain. The energy absorption efficiency of such a material is calculated as ratio of the actual volumetric energy absorbed to the maximum possible volumetric energy absorption.

[0007] Therefore, there is still a demand for lattice architectures with the inherent structural and low mass benefits, yet with improved energy absorption response.

SUMMARY

[0008] Aspects of embodiments of the present invention pertain to architected materials with superior energy absorption properties when loaded in compression. The materials possess a truss or lattice configuration with hierarchy through the thickness direction, i.e., the primary energy absorption direction, of the material, which provides enhanced energy absorption functionality versus lattice architectures in prior art while retaining their inherent structural and mass benefits. The added dimension of architectural control can be introduced to a standard lattice structure in two different embodiments.

[0009] In one embodiment of the invention, a three-dimensional lattice architecture with a thickness hierarchy includes a first surface and a second surface separated from each other (along a normal direction to at least one of the first and second surfaces) with a distance therebetween defining a thickness of the three-dimensional lattice architecture; a plurality of angled struts extending along a plurality of directions between the first surface and the second surface; a plurality of nodes connecting the plurality of angled struts with one another forming a plurality of unit cells. At least a portion of the plurality of angled struts are internally terminated along the thickness direction of the lattice structure and providing a plurality of internal degrees of freedom towards the first or second surface of the lattice architecture...

BRIEF DESCRIPTION OF THE DRAWINGS
[ PDF ]

[0014] FIG. 1 is a schematic illustration of the ideal compressive stress-strain behavior of an energy absorption material, with or without a lattice architecture.

[0015] FIG. 2 is a schematic illustration of the typical compressive stress-strain behavior of a lattice or truss structure with high structural symmetry and internal connectivity.

[0016] FIGS. 3a and 3b are schematic drawings illustrating a lattice architecture with architected thickness hierarchy introduced through the use of an architected template.

[0017] FIG. 4 is a schematic illustration of a lattice architecture with two different lattice structures stacked together.

[0018] FIG. 5a is a schematic drawing illustrating one embodiment of the process of making a lattice architecture using an architected template.

[0019] FIG. 5b is a schematic drawing illustrating another embodiment of the process of making a lattice architecture using an architected template.

[0020] FIG. 6a shows a bottom view of one exemplary lattice architecture prior to the introduction of interrupted internal members.

[0021] FIG. 6b shows the bottom view of the exemplary lattice architecture shown in FIG. 6a with an architected template superimposed on the lattice architecture.

[0022] FIG. 6c shows the bottom view of the exemplary lattice architecture shown in FIG. 6a after the introduction of interrupted internal members formed by using the architected template shown in FIG. 6b.

[0023] FIG. 6d shows a cross-sectional view of the lattice architecture shown in FIG. 6c along the line a-a′.

[0024] FIG. 7 shows another exemplary lattice architecture with interrupted internal members.

[0025] FIG. 8 shows one exemplary lattice architecture with interrupted internal members attached to structural facesheets at the top and bottom surfaces of the structure.

[0026] FIG. 9 shows the comparison of a simulated compressive stress-strain response of the exemplary lattice architecture shown in FIG. 7 versus a similar lattice structure without the interrupted members.

[0027] FIG. 10 shows the comparison of a simulated compressive stress-strain response of the exemplary lattice architecture shown in FIG. 8 versus a similar lattice structure without the interrupted members.

[0028] FIG. 11 is a schematic drawing illustrating one embodiment of the process of making a lattice architecture with multiple lattice structures stacked together.

[0029] FIG. 12 is a photograph of an actual lattice architecture with two different lattice structures stacked together.

[0030] FIG. 13 is a schematic illustration of a lattice architecture with three different lattice structures stacked together including facesheet materials at the interfaces between lattices with dissimilar architectures

[0031] FIG. 14 shows the compressive stress-strain response of the material shown in FIG. 12 under compression.

[0032] FIG. 15 shows photographs of the lattice architecture of FIG. 12 composed of two different layers of lattice structures stacking together under compression.
 


US9096722
A METHOD FOR CURING STRUCTURES USING A DUAL PHOTOINITIATOR SYSTEM AND A STRUCTURE MADE USING THE SAME

Inventor(s): YANG SOPHIA, et al.

A monomeric formulation for fabrication of microlattice structures, the monomeric formulation including a plurality of monomers, a first photoinitiator configured to substantially activate above a wavelength of light, and a second photoinitiator configured not to substantially activate above the wavelength of light and to substantially activate below the wavelength of light.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority to and the benefit of U.S. Patent Application No. 61/893,001, filed on Oct. 18, 2013, the entire content of which is incorporated herein by reference.

This application is related to a U.S. patent application entitled “Net-Shape Structure with Micro-Truss Core” (U.S. application Ser. No. 13/312,952), filed on Dec. 6, 2011, is related to a U.S. patent entitled “Functionally Graded Three-Dimensional Ordered Open-Cellular Microstructure and Method of Making the Same” (U.S. Pat. No. 8,195,023), issued on Jun. 5, 2012, and is also related to a U.S. patent entitled “Optically Oriented Three-Dimensional Polymer Microstructures” (U.S. Pat. No. 7,653,279), issued on Jan. 6, 2010, the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to methods for curing structures in a net shape, and, more particularly, to methods for curing the structure utilizing a dual photoinitiator system, and to structures produced thereby.

BACKGROUND

Lightweight sandwich structures, that is, structures including a core sandwiched between two facesheets, are utilized for a variety of purposes including heat exchangers, padding (e.g., in seats, cushions, helmets, shoe insoles, mattresses, etc.), advanced armor applications (e.g., blast protection), high impact/low weight applications (such as bumper beams, battery trays, wings), and/or the like. In some applications, it may be beneficial to shape lightweight sandwich structures into particular curvatures that conform to a surface where the structure will be utilized. In some instances, framing a sandwich structure into a particular shape may require costly manufacturing techniques.

Generally, the materials utilized for lightweight sandwich structures dictate how the structure is formed and whether it can be formed to have complex curvatures. Existing materials utilized as cores for lightweight sandwich structures include foams, honeycomb, and metal lattice structures. Each of these materials has limitations in its ability to conform to particular curvatures.

Foams can be either open-cellular or closed cellular and are available in a variety of materials including, but not limited to, polymers, metals, and ceramics. Open-cellular foams generally have limited strength and stiffness, which limits their usefulness in a variety of applications. Open-cellular foams also have tortuous, non-uniform paths for fluid flow, in which high pressures are often utilized to force fluid through the structure. Closed-cellular foams have greater strength and rigidity than open-cellular foams, making them more suitable as cores for sandwich structures. However, closed-cellular foams do not permit fluid to freely flow through the material, which limits their usefulness in applications where fluid flow is required, such as heat transfer applications. Generally, machining is utilized to form foam into a particular curvature.

Honeycomb structures are also available in a number of different materials including, but not limited to, aluminum, and thermoplastic polymers. Generally, honeycomb structures are closed-cellular. In order to achieve a particular curvature with a honeycomb structure a specific corresponding unit cell shape is generally utilized. This approach may work for a structure requiring a single radius of curvature; however, it is less effective for complex curvatures which have more than one radius of curvature.

Metallic lattice structures have good strength and stiffness properties and may also function as fluid heat exchanges because the structures allow low pressure drop fluid flow through the material. However, to form a metal lattice structure into a particular curvature, the structure is generally plastically deformed or machined.

As such, what is desired is a lightweight structure that can be easily formed to have a particular curvature without resorting to pre- or post-production manufacturing, which may be time consuming, expensive, and/or may damage the structural integrity of the sandwich structure.

SUMMARY

Aspects of embodiments of the present invention are directed to curing structures in net shape by utilizing a combination of different photoinitiators and different wavelength light sources.

Aspects of embodiments of the present invention are directed toward forming and curing a microlattice structure by forming a compliant (e.g., pliable) precursor structure through activating a first photoinitiator of a resin formulation by a light (e.g., ultraviolet (UV) light) of a first wavelength and first intensity, shaping the precursor structure, if desired, and post-curing the precursor structure through activating a second photoinitiator of the resin formulation by a light (e.g., UV light) of a second wavelength and a second intensity, where the second wavelength is shorter than the first wavelength and the second intensity is greater than the first intensity.

According to embodiments of the present preset invention, there is provide a monomeric formulation for fabrication of microlattice structures, the monomeric formulation including: a plurality of monomers; a first photoinitiator configured to substantially activate above a wavelength of light; and a second photoinitiator configured not to substantially activate above the wavelength of light and to substantially activate below the wavelength of light...

BRIEF DESCRIPTION OF THE DRAWINGS
[ PDF ]

These and other features and advantages of the present invention will be better understood by reference to the following detailed description when considered in conjunction with the following drawings, in which like elements are referenced with like numerals. These drawings should not be construed as limiting the present invention, but are intended to be illustrative only.

FIG. 1 is a schematic cross-sectional diagram illustrating a dual photoinitiator system (e.g., a dual cure system) for forming a three-dimensional structure, according to an illustrative embodiment of the present invention.

FIG. 2A illustrates the UV absorption spectra of example photoinitiators that are active at longer wavelengths utilized as the first photoinitiators of the resin formulation, according to an illustrative embodiment of the present invention. FIG. 2B illustrates the UV absorption spectra of example photoinitiators that are active at shorter wavelengths utilized as the second photoinitiators of the resin formulation, according to an illustrative embodiment of the present invention.

FIG. 3 illustrates the light absorption spectra of the first and second photoinitiators and the wavelengths of lights utilized during the dual curing stages of the dual photoinitiator system, according to an embodiment of the present invention.

FIGS. 4A-4B respectively illustrate a cross-section of a flat unconstrained microlattice structure, and one that is shaped utilizing a method of net-shaping, according to an illustrative embodiment of the present invention.

FIG. 5 is a flow diagram of a process for curing microlattice materials by utilizing the dual cure system, according to an illustrative embodiment of the present invention.



US2015176132
STRUCTURES HAVING SELECTIVELY METALLIZED REGIONS AND METHODS OF MANUFACTURING THE SAME

Methods of manufacturing a structure having at least one plated region and at least one unplated region. The method includes plating a metal on a polymer structure having a first region accepting the metal and a second region unreceptive to the metal plating. The first region may include fully-cured polymer optical waveguides and the second region may include partially-cured polymer optical waveguides. The first region may include a first polymer composition and the second region may include a second polymer composition different than the first polymer composition.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to and the benefit of U.S. Provisional Application No. 61/918,540, filed Dec. 19, 2013, the entire content of which is incorporated herein by reference.

FIELD

[0002] The present invention relates generally to polymer structures and, more particularly, to partially metallized polymer structures.

BACKGROUND

[0003] Metallized components are ubiquitous. Components are commonly metallized for aesthetic, structural, conductive, and/or corrosion resistance purposes. Related processes for metallizing components include painting, dipping, electroplating, electroless plating, spraying, sputtering, and laser activation. Processes for metallizing components are typically directed at uniformly coating the component. Non-metallized portions of the component are typically the result of uncontrollable variation, which is indicative of an unsuccessful process and therefore such partially metallized components are typically discarded.

[0004] Additionally, related processes for metallizing components are typically limited to line-of-sight coverage of the component. For instance, related metallizing processes may be limited to metallizing only external surfaces of the component. Additionally, related metallizing processes may be restricted to components having limited sizes and geometries (e.g., related metallizing techniques may be limited to the two-dimensional coating of flat components, such as circuit boards). Thus, related metallizing processes may be suitable only for components having limited sizes and architectures.

SUMMARY

[0005] Aspects of embodiments of the present disclosure are directed toward various methods for manufacturing a structure having at least one plated region and at least one unplated region. In one embodiment, the method includes plating a metal on a polymer structure having a first region accepting the metal and a second region unreceptive to the metal. The polymer structure may include a plurality of interconnected polymer optical waveguides arranged in a unitary lattice structure. Plating the polymer structure may include conditioning the polymer structure, etching the polymer structure, neutralizing the polymer structure, catalyzing the polymer structure, immersing the polymer structure in an accelerator, and immersing the polymer structure in an electroless bath. Plating the polymer structure may include a catalyst poisoning method, an inhibition of metal reaction method, an over-etched polymer surface method, an increased etch rate-post process method, an uncured surface inhibition of plating method, or an etch resistant polymer-prevention of catalyst deposition method. The first region may include fully-cured, cross-linked polymer optical waveguides and the second region may include partially-cured polymer optical waveguides. The first region may include a first polymer composition, and the second region may include a second polymer composition different than the first polymer composition.

[0006] The method may also include immersing the polymer structure in a catalyst inhibitor that deposits onto the second region of the polymer structure and is repelled by the first region of the polymer structure. The method may also include immersing the polymer structure in a reaction inhibitor that deposits onto the second region of the polymer structure and is repelled by the first region of the polymer structure. The method may also include etching the polymer structure. The first region of the polymer structure may etch at a first rate and the second region of the polymer structure may etch at a second rate different than the first rate. The method may also include forming the polymer structure by irradiating one or more photo-monomers with a series of light beams. The polymer structure may include a series of interconnected polymer optical waveguides arranged in a unitary lattice structure. The method may also include forming the polymer structure by irradiating a volume of a first photo-monomer with a series of light beams to form the first region of the polymer structure and irradiating a volume of a second photo-monomer with a series of light beams to form the second region of the polymer structure. The method may also include forming the polymer structure by an additive manufacturing process, such as stereolithography, digital light processing, fused deposition, or selective laser sintering.

[0007] In another embodiment, the method includes irradiating a volume of a first photo-monomer with a series of light beams to form a first region of a polymer structure and irradiating a volume of a second photo-monomer different than the first photo-monomer with a series of light beams to form a second region of the polymer structure coupled to the first region of the polymer structure. One of the first and second regions of the polymer structures accepts metal plating and the other one of the first and second regions of the polymer structure rejects metal plating. The method may also include plating the first or second region of the polymer structure that accepts metal plating. The method may also include metal plating the other one of the first and second regions of the polymer structure and removing the polymer structure by etching to form a plurality of interconnected hollow struts...

BRIEF DESCRIPTION OF THE DRAWINGS
[ PDF ]

[0011] These and other features and advantages of embodiments of the present disclosure will become more apparent by reference to the following detailed description when considered in conjunction with the following drawings. In the drawings, like reference numerals are used throughout the figures to reference like features and components. The figures are not necessarily drawn to scale.

[0012] FIGS. 1A-1K are side views of partially metallized three-dimensional structures according to various embodiments of the present disclosure;

[0013] FIGS. 2A-2C illustrate tasks of forming a polymer structure having one or more regions receptive to metal plating and one or more regions unreceptive to metal plating according to one embodiment of the present disclosure;

[0014] FIG. 3 is a flowchart illustrating tasks of metallizing the one or more regions of the polymer structure of FIG. 2C that are receptive to metal plating according to one embodiment of the present disclosure;

[0015] FIG. 4 is a partial side view of a series of interconnected hollow struts according to one embodiment of the present disclosure;

[0016] FIGS. 5A-5C illustrate tasks of forming a polymer structure having one or more regions receptive to metal plating and one or more regions unreceptive to metal plating according to another embodiment of the present disclosure;

[0017] FIG. 6 illustrates tasks of forming a polymer structure having one or more regions receptive to metal plating and one or more regions unreceptive to metal plating according to a further embodiment of the present disclosure;

[0018] FIGS. 7A-7D illustrate tasks of forming a polymer structure having one or more regions receptive to metal plating and one or more regions unreceptive to metal plating according to another embodiment of the present disclosure; and

[0019] FIGS. 8A and 8B illustrate tasks of forming a polymer structure having one or more regions receptive to metal plating and one or more regions unreceptive to metal plating according to one embodiment of the present disclosure.
 


US8195023
FUNCTIONALLY-GRADED THREE-DIMENSIONAL ORDERED OPEN-CELLULAR MICROSTRUCTURE AND METHOD OF MAKING SAME


A method for creating or forming a functionally graded 3D ordered open-cellular microstructure, and a functionally graded 3D ordered open-cellular microstructure. In one embodiment, the functionally-graded three-dimensional ordered open-cellular microstructure includes a first three-dimensional interconnected pattern of polymer waveguides having a first three-dimensional pattern; a second three-dimensional interconnected pattern of polymer waveguides having a second three-dimensional pattern differing from the first three-dimensional pattern; and an interface connected with the first three-dimensional interconnected pattern of polymer waveguides and the second three-dimensional interconnected pattern of polymer waveguides. Here, the term "functionally graded" refers to a spatial variation in the physical microstructure-and thus the properties-through the thickness of the material.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application relates to U.S. patent application Ser. No. 11/580,335, filed on Oct. 13, 2006, entitled “Optically Oriented Three-Dimensional Polymer Microstructures” and to U.S. patent application Ser. No. 11/801,908, filed on May 10, 2007, entitled “Three-Dimensional Ordered Open-Cellular Structures.” The entire contents of each of the above-referenced applications are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a three-dimensional (3D) ordered open-cellular microstructure and a method to fabricate such a material. In particular, the present invention relates to a functionally graded 3D ordered open-cellular microstructure and a method of making the same.

BACKGROUND OF THE INVENTION

A three-dimensional (3D) ordered open-cellular microstructure is an ordered 3D structure at the micrometer scale. Aspects of embodiments of the present invention are directed toward a functionally graded 3D ordered open-cellular microstructure and a method of making the same. Here, the term “functionally graded” refers to a spatial variation in the physical microstructure—and thus the properties—through the thickness of the material.

A 3D ordered open-cellular microstructure can be formed, for example, by using a stereolithography technique, which relies on a bottom-up, layer-by-layer approach. This process usually involves a platform (substrate) that is lowered into a photo-monomer (photopolymer) bath in discrete steps. At each step, a laser is scanned over the area of the photo-monomer that is to be cured (polymerized) for that particular layer. Once the layer is cured, the platform is lowered a specific amount (determined by the processing parameters and desired feature/surface resolution) and the process is repeated until the full 3D structure is created.

One example of such a stereolithography technique is disclosed in Hull et al., “Apparatus For Production Of Three-Dimensional Objects By Stereolithography,” U.S. Pat. No. 4,575,330, Mar. 11, 1986, which is incorporated by reference herein in its entirety.

Modifications to the above described stereolithography technique have been developed to improve the resolution with laser optics and special resin formulations, as well as modifications to decrease the fabrication time of the 3D structure by using a dynamic pattern generator to cure an entire layer at once. One example of such a modification is disclosed in Bertsch et al., “Microstereolithography: A Review,” Materials Research Society Symposium Proceedings, Vol. 758, 2003, which is incorporated by reference herein in its entirety. A fairly recent advancement to the standard stereolithography technique includes a two-photon polymerization process as disclosed in Sun et al., “Two-Photon Polymerization And 3D Lithographic Microfabrication,” APS, Vol. 170, 2004, which is incorporated by reference herein in its entirety. However, this advance process still relies on a complicated and time consuming layer-by-layer approach.

Previous work has also been done on creating polymer optical waveguides. A polymer optical waveguide can be formed in certain photopolymers that undergo a refractive index change during the polymerization process. If a monomer that is photo-sensitive is exposed to light (typically UV) under the right conditions, the initial area of polymerization, such as a small circular area, will “trap” the light and guide it to the tip of the polymerized region due to this index of refraction change, further advancing that polymerized region. This process will continue, leading to the formation of a waveguide structure with approximately the same cross-sectional dimensions along its entire length. The existing techniques to create polymer optical waveguides have only allowed one or a few waveguides to be formed and these techniques have not been used to create a self-supporting three-dimensional structure by patterning polymer optical waveguides.

In addition, functionally graded foams with random cell configurations have been fabricated through various techniques and are discussed in Lefebvre et al., “Method Of Making Open Cell Material,” U.S. Pat. No. 7,108,828, Sep. 19, 2006; in Lauf et al., “Method Of Making A Functionally Graded Material,” U.S. Pat. No. 6,375,877, Apr. 23, 2002; and in Vyakarnam et al., “Porous Tissue Scaffoldings For The Repair Or Regeneration Of Tissue,” U.S. Pat. No. 6,534,084, Mar. 18, 2003; the entire contents of each of which are incorporated herein by reference. However, these functionally graded structures with specifically designed and ordered microstructures rely on layer-by-layer approaches similar to the above discussed stereolithography techniques, an example of which is also discussed in Keicher et al., “Forming Structures From CAD Solid Models”, U.S. Pat. No. 6,391,251, May 21, 2002, which is incorporated herein by reference in its entirety. These above cited references do not, however, disclose or discuss a manufacturing technique for 3D patterning of self-propagating polymer optical waveguides to form functionally graded open-cellular microstructures.

As such, there continues to be a need for 3D patterning of self-propagating polymer optical waveguides to form functionally graded 3D ordered open-cellular microstructures (or open-cellular materials) on a large and useful scale using a simple technique...

SUMMARY OF THE INVENTION

An aspect of an embodiment of the present invention is directed toward a method for creating or forming a functionally graded 3D ordered open-cellular microstructure.

BRIEF DESCRIPTION OF THE DRAWINGS
[ PDF ]

The accompanying drawings, together with the specification, illustrate exemplary embodiments of the present invention, and, together with the description, serve to explain the principles of the present invention.

FIG. 1 is a perspective schematic view of a portion of a structure according to an embodiment of the present invention.

FIG. 2 is a perspective schematic view of a structure according to an embodiment of the present invention.

FIG. 3 is a schematic diagram of a system for forming a structure of an embodiment of the present invention from multiple waveguides created using a single collimated beam or multiple collimated beams through multiple apertures.

FIG. 4a illustrates an example of a square mask pattern (or a square mask aperture pattern) according to embodiments of the present invention.

FIG. 4b illustrates an example of a hexagonal mask pattern (or a hexagonal mask aperture pattern) according to embodiments of the present invention.

FIG. 5 is a process flow diagram for forming one or more polymer waveguides of a structure according to an embodiment of the present invention.

FIG. 6 is a perspective schematic view showing respective directions along which truss elements of a structure of an embodiment of the present invention extend.

FIG. 7 is schematic diagram of a system for forming a functionally graded 3D ordered open-cellular microstructure according to an embodiment of the present invention.

FIG. 8 illustrates a top view schematic of a system for forming a functionally graded 3D ordered open-cellular microstructure according to an embodiment of the present invention.

FIGS. 9a, 9b, and 9c represent 2D schematics of three-dimensional functionally graded microstructures according to embodiments of the present invention.

FIG. 10 is a process flow diagram for forming a functionally graded 3D ordered open-cellular microstructure according to an embodiment of the present invention.



US7382959
OPTICALLY ORIENTED THREE-DIMENSIONAL POLYMER MICROSTRUCTURES

A method and system of creating one or more waveguides and/or patterning these waveguides to form a 3D microstructure that uses mask and collimated light. In one embodiment, the system includes at least one collimated light source selected to produce a collimated light beam; a reservoir having a photo-monomer adapted to polymerize by the collimated light beam; and a mask having at least one aperture and positioned between the at least one collimated light source and the reservoir. Here, the at least one aperture is adapted to guide a portion of the collimated light beam into the photo-monomer to form the at least one polymer waveguide through a portion of a volume of the photo-monomer.

FIELD OF THE INVENTION

The present invention relates to patterning one or more polymer waveguides to form an ordered three-dimensional (3D) microstructure and/or a system and method to fabricate the one or more polymer waveguides.

BACKGROUND OF THE INVENTION

An ordered three-dimensional (3D) microstructure is an ordered 3D structure at the micrometer scale. Currently, polymer cellular materials that are mass produced are created through various foaming processes, which all yield random (not ordered) 3D microstructures. Techniques do exist to create polymer materials with ordered 3D microstructures, such as stereolithography techniques; however, these techniques rely on a bottom-up, layer-by-layer approach which prohibits scalability.

A stereolithography technique is a technique that builds a 3D structure in a layer-by-layer process. This process usually involves a platform (substrate) that is lowered into a photo-monomer (photopolymer) bath in discrete steps. At each step, a laser is scanned over the area of the photo-monomer that is to be cured (polymerized) for that particular layer. Once the layer is cured, the platform is lowered a specific amount (determined by the processing parameters and desired feature/surface resolution) and the process is repeated until the full 3D structure is created. One example of such a stereolithography technique is disclosed in Hull et al., "Apparatus For Production Of Three-Dimensional Objects By Stereolithography," U.S. Pat. No. 4,575,330, Mar. 11, 1986, which is incorporated by reference herein in its entirety.

Modifications to the above described stereolithography technique have been developed to improve the resolution with laser optics and special resin formulations, as well as modifications to decreasing the fabrication time of the 3D structure by using a dynamic pattern generator to cure an entire layer at once. One example of such a modification is disclosed in Bertsch et al., "Microstereolithography: A Review," Materials Research Society Symposium Proceedings, Vol. 758, 2003, which is incorporated by reference herein in its entirety. A fairly recent advancement to the standard stereolithography technique includes a two-photon polymerization process as disclosed in Sun et al., "Two-Photon Polymerization And 3D Lithographic Microfabrication," APS, Vol. 170, 2004, which is incorporated by reference herein in its entirety. However, this advance process still relies on a complicated and time consuming layer-by-layer approach.

3D ordered polymer cellular structures have also been created using optical interference pattern techniques, also called holographic lithography; however, structures made using these techniques have an ordered structure at the nanometer scale and the structures are limited to the possible interference patterns, as described in Campbell et al., "Fabrication Of Photonic Crystals For The Visible Spectrum By Holographic Lithography," NATURE, Vol. 404, Mar. 2, 2000, which is incorporated by reference herein in its entirety.

Previous work has also been done on creating polymer optical waveguides. A polymer optical waveguide can be formed in certain photopolymers that undergo a refractive index change during the polymerization process. If a monomer that is photo-sensitive is exposed to light (typically UV) under the right conditions, the initial area of polymerization, such as a small circular area, will "trap" the light and guide it to the tip of the polymerized region due to this index of refraction change, further advancing that polymerized region. This process will continue, leading to the formation of a waveguide structure with approximately the same cross-sectional dimensions along its entire length. The existing techniques to create polymer optical waveguides have only allowed one or a few waveguides to be formed and these techniques have not been used to created a self-supporting three-dimensional structure by patterning polymer optical waveguides.
As such, there continues to be a need to create polymer cellular materials with ordered microstructures on a large and useful scale using a simple technique.

SUMMARY OF THE INVENTION

An aspect of the present invention provides a method and system of fabricating polymer cellular (porous) materials with an ordered three-dimensional (3D) microstructure using a simple technique. These cellular materials are created from a pattern of self-propagating polymer waveguides, which are formed in an appropriate photopolymer. This method and system can create truly 3D microstructures without building the structures layer-by-layer as with stereolithography and other prototyping techniques.

Another aspect of the present invention creates polymer cellular materials with ordered microstructures on a large and useful scale.

In an embodiment of the present invention, a system for forming at least one polymer waveguide is provided. The system includes at least one light source selected to produce a light beam; a reservoir having a photo-monomer adapted to polymerize by the light beam; and a patterning apparatus adapted to guide a portion of the light beam into the photo-monomer to form the at least one polymer waveguide through a portion of a volume of the photo-monomer.

In one embodiment of the system, the at least one light source includes at least one collimated light source, the light beam is a collimated light beam, the patterning apparatus includes a mask having at least one aperture and positioned between the at least one collimated light source and the reservoir, and the at least one aperture is adapted to guide the portion of the collimated light beam into the photo-monomer to form the at least one polymer waveguide through the portion of the volume of the photo-monomer...

BRIEF DESCRIPTION OF THE DRAWINGS
[ PDF ]

The accompanying drawings, together with the specification, illustrate exemplary embodiments of the present invention, and, together with the description, serve to explain the principles of the present invention.

FIG. 1 is a schematic diagram of a system to form a single waveguide from a single collimated beam through a single aperture pursuant to aspects of the present invention;

FIG. 2 illustrates examples of different aperture shapes pursuant to aspects of the present invention;

FIG. 3 is a schematic diagram of a system to form multiple waveguides from a single collimated beam or multiple collimated beams through a single aperture pursuant to aspects of the present
invention;

FIG. 4 is a schematic diagram of a system to form a 3D structure (e.g., a 3D ordered polymer microstructure) formed from multiple waveguides created using a single collimated beam or multiple collimated beams through multiple apertures pursuant to aspects of the present invention;

FIG. 5a illustrates an example of a square mask pattern (or a square mask aperture pattern) pursuant to aspects of the present invention;

FIG. 5b illustrates an example of a hexagonal mask pattern (or a hexagonal mask aperture pattern) pursuant to aspects of the present invention;

FIG. 6 is a process flow diagram for forming one or more polymer waveguides pursuant to aspects of the present invention;

FIGS. 7a, 7b, 7c, and 7d are SEM micrographs of a sample 3D polymer microstructure pursuant to aspects of the present invention;

FIG. 8 is a 3D diagram for illustrating a formation of a 3D ordered polymer microstructure pursuant to aspects of the present invention; and

FIG. 9 is another 3D diagram for illustrating a formation of a 3D ordered polymer microstructure pursuant to aspects of the present invention.
 


US8353240
Compressible fluid filled micro-truss for energy absorption


A kinetic energy and blast energy absorbing material includes: a micro-truss structure including: a plurality of first struts extending along a first direction; a plurality of second struts extending along a second direction; and a plurality of third struts extending along a third direction; and a compressible fluid comprising a liquid or gel and a nanoporous material, wherein the micro-truss structure contains the compressible fluid.

BACKGROUND

Cellular, or porous, materials have the ability to absorb significantly more energy than solid structures because of their ability to become denser (e.g., “densify”) in response to impacts. As such, cellular materials such as metallic or ceramic foams have been proposed as an energy absorbing layer in armor-type systems. However, the random microstructure of these materials severely diminishes their mechanical properties. The deformation of a cellular foam is dominated by the bending behavior of the cell struts. Simple mechanics dictates that bending dominated structures are less efficient in load carrying capacity than compression dominated behavior exemplified by a truss structure. Due this mechanical inefficiency, some fraction of the mass in the foam does not participate in energy absorption and represents added or parasitic weight.

U.S. Pat. Nos. 6,698,331 and 7,128,963, which are incorporated by reference herein in their entirety, propose blast protection material systems that incorporate random cellular ceramic or metallic foam as an energy absorbing layer. However, these patent disclosures do not provide an ordered micro-truss structure. The use of metallic lattice (truss) materials for energy absorbing application is discussed in U.S. Pat. No. 7,382,959 and U.S. patent application Ser. Nos. 11/801,908; 12/008,479; 12/074,727, 12/075,033, and 12/455,449 which are incorporated by reference herein in their entirety. Methods of manufacturing a micro-truss structure are described, for example, in U.S. patent application Ser. No. 12/455,449, which discloses a method of fabricating micro-truss structures having a fixed area, and 12/835,276, which discloses a method of continuously fabricating micro-truss structures according to a continuous process (e.g., a strip of arbitrary length), which are incorporated by reference herein in their entirety. However, there is still a demand for an impact or blast energy absorbing material that is light weight.

Compressible fluids have the ability to absorb a significant amount of energy. U.S. patent application Ser. No. 11/720,784, which is incorporated by reference herein in its entirety, describes a compressible fluid which may include a nanoporous material immersed in a non-wetting liquid which is compressed when external forces push the liquid into the nanopores of the material.

An explosive blast typically comprises an air pressure wave characterized by an overpressure P0 in excess of the ambient pressure Pa (and where P0/e and ti indicate that the pressure drops exponentially) with an associated impulse per unit area, as illustrated, e.g., in FIGS. 11a and 11b. In order for an intervening medium to protect a structure against the overpressure P0, the medium must reduce the pressure below the structure's damage threshold σth. This can be achieved by the intervening medium's undergoing a large volume decrease at a constant pressure, thereby extending the duration of the impulse.

The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person skilled in the art.

SUMMARY

Aspects of embodiments of the present invention relate to a micro-truss based structural apparatus with compressible fluid for absorbing energy from impacts or pressure waves (e.g., a fluidic micro-truss based impact or blast protection apparatus).

Aspects of embodiments of the present invention are directed toward a fluidic micro-truss based blast protection apparatus which is capable of absorbing energy from an impact or a pressure wave. Aspects of embodiments of the present invention are directed toward a fluidic micro-truss blast protection system which may be used as a component of personal armor, a component of vehicle armor (e.g., on a Humvee), or a component of a blast protection wall (e.g., a Bremer wall) in order to provide additional protection against collisions, projectiles (e.g., bullets), and blasts (e.g., from improvised explosive devices (IEDs)).

Aspects of embodiments of the present invention are also directed toward a fluidic micro-truss blast protection system which may be used on internal surfaces of a vehicle to provide additional protection for passengers.

According to embodiments of the present invention, polymer micro-truss structures, which are formed by interconnecting self-propagating polymer waveguides (or struts), are converted to lightweight, high-strength materials such as carbon, metals, ceramics, or polymers (e.g., high toughness polymers) or composites thereof, that are utilized by the micro-truss based protection apparatuses for high velocity impact or pressure wave applications. According to embodiments of the present invention, these micro-truss structures are combined with a compressible fluid, e.g., a suspension of nanoporous particles in a liquid or gel (which may be referred to as a “nanoporous-materials-functionalized (NMF) fluid”), to provide additional energy absorbing characteristics.

According to one embodiment of the present invention, a kinetic energy and blast energy absorbing material includes: a micro-truss structure including: a plurality of first struts extending along a first direction; a plurality of second struts extending along a second direction; and a plurality of third struts extending along a third direction; and a compressible fluid comprising a liquid or gel and a nanoporous material, wherein the micro-truss structure contains the compressible fluid.

The compressible fluid may be a compressible nano-porous materials functionalized (NMF) fluid. The NMF fluid may be a liquid or a gel. The NMF fluid may include a nanoporous material and an infiltration fluid, wherein the infiltration fluid is nonwetting to the nanoporous material. The nanoporous particles may be silica based nanoporous particles. The nanoporous particles may be a hydrophobic zeolite. The nanoporous particles may be a nanoporous carbon. The nanoporous carbon may be a mercaptohexadecanoic acid (MHA) treated nanoporous carbon.

The nanoporous particles may have a surface area at 100 m<2>/g or 2000 m<2>/g or between 100 m<2>/g and 2000 m<2>/g.

The infiltration fluid may include water, an aqueous solution of electrolytes, a viscous liquid, a liquid metal, a gel, a polymer, or a combination thereof.

The struts of the kinetic energy and blast energy absorbing material may be hollow.

The compressible fluid may be located within the hollow struts.

Each of the hollow struts may have a diameter from 10 microns to 10 mm.

A wall of each of the struts may have a thickness from 1 micron to 1 mm.

The compressible fluid may be located between the struts.

The kinetic energy and blast absorbing material may be configured to be part of a protective piece of clothing.

The kinetic energy and blast energy absorbing material may be configured to be part of a wall of a building.

The first, second, and third struts may include a metal. The metal may be nickel, aluminum, titanium, steel, or alloys thereof.

The first, second, and third struts may include a polymer. The polymer may be a polycarbonate, an aramid, a high impact polystyrene, a nylon, an ultra-high molecular weight polyethylene, and combinations thereof.

The micro-truss structure may fill 0.5% to 30% of a volume of the material and the NMF fluid may fill 5% to 95% of the volume.

The first, second, and third directions may be at a first angle between 45° and 70° with respect to a facesheet attached to a plurality of first ends of the first, second, and third struts.

The kinetic energy and blast absorbing material may further include a plurality of fourth struts extending in a fourth direction substantially perpendicular with respect to a facesheet attached to a plurality of first ends of the first, second, and third struts.

The plurality of first, second, third and fourth struts may be hollow and may comprise metal and the first, second, third and fourth struts may each have a diameter of 2 mm and a wall thickness of 0.1 mm, wherein the micro-truss structure has a unit cell height of 15 mm, wherein each of the first, second, and third directions is at an angle of 60° with respect to the facesheet, wherein the compressible fluid may be an aqueous suspension of 40% by weight hydrophobic nanoporous silica gel and may be located within the hollow portions of plurality of first, second, third and fourth struts, and wherein the micro-truss structure may fill 5% of the volume of the kinetic energy and blast energy absorbing material and the compressible fluid may fill 25% of the volume of the kinetic energy and blast energy absorbing material.

The plurality of first, second, third and fourth struts may be hollow and may comprise metal and the first, second, third and fourth struts may each have a diameter of 2 mm and a wall thickness of 0.1 mm, wherein the micro-truss structure has a unit cell height of 15 mm, wherein each of the first, second, and third directions is at an angle of 60° with respect to the facesheet, wherein the compressible fluid may be an aqueous suspension of 7% by weight hydrophobic nanoporous silica gel in polyacrylic acid gel and may be located within the hollow portions of plurality of first, second, third and fourth struts, and wherein the micro-truss structure may fill 5% of the volume of the kinetic energy and blast energy absorbing material and the compressible fluid may fill 25% of the volume of the kinetic energy and blast energy absorbing material...

BRIEF DESCRIPTION OF THE DRAWINGS
[ PDF ]

The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

The accompanying drawings, together with the specification, illustrate exemplary embodiments of the present invention, and, together with the description, serve to explain the principles of the present invention.

FIG. 1 is a perspective view of a portion of an ordered 3D micro-truss structure according to aspects of the present invention.

FIG. 2 is a perspective view of an ordered 3D micro-truss structure according to aspects of the present invention.

FIG. 3a is a schematic cross-sectional diagram at an exposure area of a channel of a system for forming a structure from multiple waveguides created using a single collimated beam or multiple collimated beams passing through multiple apertures located at the bottom of the channel.

FIG. 3b is a schematic cross-sectional diagram at an exposure area of a channel of a system similar to that of FIG. 3a, but where the collimated beam or beams pass through multiple apertures located above the channel.

FIG. 4a illustrates a square mask pattern (or a square mask aperture pattern) according to an embodiment of the present invention.

FIG. 4b illustrates a hexagonal mask pattern (or a hexagonal mask aperture pattern) according to an embodiment of the present invention.

FIG. 5 is a schematic representation of a system for forming an ordered 3D micro-truss structure according to an embodiment of the present invention from multiple waveguides created using a single collimated beam or multiple collimated beams through multiple apertures and a moving mask.

FIG. 6 is a photograph of a micro-truss structure according to one embodiment of the present invention.

FIG. 7 is a graph comparing compressive stress as a function of nominal strain for micro-truss structures with and without 90° truss members (as depicted) having relative densities of 1.8% and 1.4% respectively, according to one embodiment of the present invention.

FIG. 8a is a graph comparing sorption isotherm curves for zeolite based NMF fluids including a solution of NaCl at a variety of concentrations according to one embodiment of the present invention.

FIG. 8b is a graph comparing sorption isotherm curves for carbon based NMF fluids in which the carbon surface treating carbon surfaces with mercaptohexadecanoic acid (MHA) according to one embodiment of the present invention.

FIG. 8c is a graph comparing sorption isotherm curves of a silica based NMF fluid in glycerin-water mixtures having a variety of concentrations of glycerin according to one embodiment of the present invention.

FIG. 8d is a graph comparing sorption isotherm curves of a nanoporous carbon in polypropylene during first and second loadings according to one embodiment of the present invention.

FIG. 8e is a graph comparing sorption isotherm curves of a silica based gel matrix NMF fluid during successive infiltration cycles according to one embodiment of the present invention.

FIG. 8f is a graph comparing sorption isotherm curves of a carbon based NMF fluid in mercury during first and second loadings according to one embodiment of the present invention.

FIG. 8g is a graph comparing sorption isotherm curves of a silica based NMF fluid in which the silica particles have been treated for various amounts of time according to one embodiment of the present invention.

FIG. 9 is a graph illustrating a relationship between pressure and specific volume change for an NMF fluid during a plurality of cycles according to one embodiment of the present invention.

FIGS. 10a and 10b illustrate the effect of a blast on a micro-truss structure according to one embodiment of the present invention (figure adapted from A. G. Evans, M. Y. He, V. S. Deshpande, J. W. Hutchinson, A. J. Jacobsen, W. B. Carter, “Concepts for enhanced energy absorption using hollow micro-lattices,” Int. Journal of Impact Engineering 37 (9), p. 947-959 (2010)).

FIG. 11 illustrates the effect the effect of a blast on a fluidic micro-truss structure in which an NMF fluid is located within hollow struts of the micro-truss structure according to one embodiment of the present invention.

FIG. 12 is a graph comparing the energy absorbed per unit mass versus transmitted stress for a variety of energy absorbing materials in a non-dimensional form that distinguishes topology effects from the influence of material properties. The projected best performance of a fluidic micro-truss structure according to one envisioned embodiment of the present invention is included. (Figure adapted from A. G. Evans, M. Y. He, V. S. Deshpande, J. W. Hutchinson, A. J. Jacobsen, W. B. Carter, “Concepts for enhanced energy absorption using hollow micro-lattices,” Int. Journal of Impact Engineering 37 (9), p. 947-959 (2010).)

FIG. 13 illustrates the effect of a blast on a fluidic micro-truss structure in which an NMF fluid is located between the struts of the micro-truss structure according to one embodiment of the present invention.

FIG. 14 illustrates an application of a fluidic micro-truss structure according to one embodiment of the present invention in which the fluidic micro-truss structure is used to provide blast protection for a vehicle.



WO2015095617
STRUCTURES HAVING SELECTIVELY METALLIZED REGIONS AND METHODS OF MANUFACTURING THE SAME

Methods of manufacturing a structure having at least one plated region and at least one unplated region. The method includes plating a metal on a polymer structure having a first region accepting the metal and a second region unreceptive to the metal plating. The first region may include fully-cured polymer optical waveguides and the second region may include partially-cured polymer optical waveguides. The first region may include a first polymer composition and the second region may include a second polymer composition different than the first polymer composition.

FIELD

[0001] The present invention relates generally to polymer structures and, more particularly, to partially metallized polymer structures.

BACKGROUND

[0002] Metallized components are ubiquitous. Components are commonly metallized for aesthetic, structural, conductive, and/or corrosion resistance purposes. Related processes for metallizing components include painting, dipping, electroplating, electroless plating, spraying, sputtering, and laser activation. Processes for metallizing components are typically directed at uniformly coating the component. Non-metallized portions of the component are typically the result of uncontrollable variation, which is indicative of an unsuccessful process and therefore such partially metallized components are typically discarded.

[0003] Additionally, related processes for metallizing components are typically limited to line-of-sight coverage of the component. For instance, related metallizing processes may be limited to metallizing only external surfaces of the component. Additionally, related metallizing processes may be restricted to components having limited sizes and geometries (e.g., related metallizing techniques may be limited to the two-dimensional coating of flat components, such as circuit boards). Thus, related metallizing processes may be suitable only for components having limited sizes and architectures.

SUMMARY

[0004] Aspects of embodiments of the present disclosure are directed toward various methods for manufacturing a structure having at least one plated region and at least one unplated region. In one embodiment, the method includes plating a metal on a polymer structure having a first region accepting the metal and a second region unreceptive to the metal. The polymer structure may include a plurality of interconnected polymer optical waveguides arranged in a unitary lattice structure. Plating the polymer structure may include conditioning the polymer structure, etching the polymer structure, neutralizing the polymer structure, catalyzing the polymer structure, immersing the polymer structure in an accelerator, and immersing the polymer structure in an electroless bath. Plating the polymer structure may include a catalyst poisoning method, an inhibition of metal reaction method, an over-etched polymer surface method, an increased etch rate- post process method, an uncured surface inhibition of plating method, or an etch resistant polymer- prevention of catalyst deposition method. The first region may include fully-cured, cross-linked polymer optical waveguides and the second region may include partially-cured polymer optical waveguides. The first region may include a first, polymer composition, and the second region may include a second polymer composition different than the first polymer composition.

[0005] The method may also include immersing the polymer structure in a catalyst inhibitor that deposits onto the second region of the polymer structure and is repelled by the first region of the polymer structure. The method may also include immersing the polymer structure in a reaction inhibitor that deposits onto the second region of the polymer structure and is repelled by the first region of the polymer structure. The method may also include etching the polymer structure. The first region of the polymer structure may etch at a first rate and the second region of the polymer structure may etch at a second rate different than the first rate. The method may also include forming the polymer structure by irradiating one or more photo-monomers with a series of light beams. The polymer structure may include a series of interconnected polymer optical waveguides arranged in a unitary lattice structure. The method may also include forming the polymer structure by irradiating a volume of a first photo-monomer with a series of light beams to form the first region of the polymer structure and irradiating a volume of a second photo-monomer with a series of light beams to form the second region of the polymer structure. The method may also include forming the polymer structure by an additive manufacturing process, such as stereolithography, digital light processing, fused deposition, or selective laser sintering...

BRIEF DESCRIPTION OF THE DRAWINGS
[ PDF ]

[0010] These and other features and advantages of embodiments of the present disclosure will become more apparent by reference to the following detailed description when
considered in conjunction with the following drawings. In the drawings, like reference
numerals are used throughout the figures to reference like features and components. The figures are not necessarily drawn to scale.

[0011] FIGS. 1 A-1K are side views of partially metallized three-dimensional structures 15 according to various embodiments of the present disclosure;

[0012] FIGS. 2A-2C illustrate tasks of forming a polymer structure having one or more regions receptive to metal plating and one or more regions unreceptive to metal plating according to one embodiment of the present disclosure;

[0013] FIG. 3 is a flowchart illustrating tasks of metallizing the one or more regions of the polymer structure of FIG. 2C that are receptive to metal plating according to one embodiment of the present disclosure;

[0014] FIG. 4 is a partial side view of a series of interconnected hollow struts according to one embodiment of the present disclosure;

J [0015] FIGS. 5A-5C illustrate tasks of forming a polymer structure having one or more regions receptive to metal plating and one or more regions unreceptive to metal plating according to another embodiment of the present disclosure;

[0016] FIG. 6 illustrates tasks of forming a polymer structure having one or more regions 0 receptive to metal plating and one or more regions unreceptive to metal plating according to a further embodiment of the present disclosure;

[0017] FIGS. 7A-7D illustrate tasks of forming a polymer structure having one or more regions receptive to metal plating and one or more regions unreceptive to metal plating according to another embodiment of the present disclosure; and

[0018] FIGS, 8A and 8B illustrate tasks of forming a polymer structure having one or more regions receptive to metal plating and one or more regions unreceptive to metal plating according to one embodiment of the present disclosure.




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