The present disclosure relates to the field of composite objects and to the field of forming 3D structures using 2D sheets or plies.
The ability to transform two-dimensional (2D) sheets into three-dimensional (3D) curved shapes enables a broad range of applications, including camouflage, soft robotics, deployable systems, and biomedical devices.
A number of techniques have been attempted to form 2D sheets into 3D curved shapes. Such techniques often involve cutting and/or folding. Such approaches, however, impose intrinsic Gaussian curvatures into the final shape, leading to conformal 3D surfaces free of overfolds or wrinkles. Further, cutting can weaken the material mechanically. Accordingly, there is a long-felt need in the art for improved approaches for forming 3D objects with 2D sheets.
In meeting the described needs, the present disclosure first provides a method of forming a three-dimensional (3-D) target object having a surface, the method comprising: with a cutting graph corresponding to a two-dimensional (2-D) representation of a polyhedral mesh that is representative of the 3-D target object, forming i sheets in conformity with the cutting graph, i being from 1 to n, an i-th 2-D sheet having an i-th set of cuts formed therein, an (i+1)-th 2-D sheet having a (i+1)-th set of cuts formed therein, the (i+1)-th set of cuts optionally differing from the i-th set of cuts, the sets of cuts being arranged in the n 2-D sheets such that when the n 2-D sheets are stacked and consolidated to form the 3-D target object, a minimum number of cuts overlap.
Also provided is a 3-D composite object having a surface, the 3-D composite object comprising: i stacked and consolidated sheets, i being from 1 to n, an i-th sheet having an i-th set of cuts formed therein, an (i+1)-th sheet having a (i+1)-th set of cuts formed therein, the (i+1)-th set of cuts optionally differing from the i-th set of cuts, the sets of cuts being arranged in the n sheets such that when the n sheets are stacked and consolidated to form the 3-D object, a minimum number of cuts overlap.
Further disclosed is a kit for forming a 3-D target object, comprising: i sheets in conformity with the cutting graph, i being from 1 to n, an i-th 2-D sheet having an i-th set of cuts formed therein, an (i+1)-th 2-D sheet having a (i+1)-th set of cuts formed therein, the (i+1)-th set of cuts differing from any other n−1 sets of cuts, the i sheets being formed in accordance with a cutting graph corresponding to a two-dimensional (2-D) representation of a polyhedral mesh that is representative of the 3-D target object.
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.
In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various aspects discussed in the present document. In the drawings:
The present disclosure may be understood more readily by reference to the following detailed description of desired embodiments and the examples included therein.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In case of conflict, the present document, including definitions, will control. Preferred methods and materials are described below, although methods and materials similar or equivalent to those described herein can be used in practice or testing. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. The materials, methods, and examples disclosed herein are illustrative only and not intended to be limiting.
The singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.
As used in the specification and in the claims, the term “comprising” may include the embodiments “consisting of” and “consisting essentially of” The terms “comprise(s),” “include(s),” “having,” “has,” “can,” “contain(s),” and variants thereof, as used herein, are intended to be open-ended transitional phrases, terms, or words that require the presence of the named ingredients/steps and permit the presence of other ingredients/steps. However, such description should be construed as also describing compositions or processes as “consisting of” and “consisting essentially of” the enumerated ingredients/steps, which allows the presence of only the named ingredients/steps, along with any impurities that might result therefrom, and excludes other ingredients/steps.
As used herein, the terms “about” and “at or about” mean that the amount or value in question can be the value designated some other value approximately or about the same. It is generally understood, as used herein, that it is the nominal value indicated ±10% variation unless otherwise indicated or inferred. The term is intended to convey that similar values promote equivalent results or effects recited in the claims. That is, it is understood that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but can be approximate and/or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art. In general, an amount, size, formulation, parameter or other quantity or characteristic is “about” or “approximate” whether or not expressly stated to be such. It is understood that where “about” is used before a quantitative value, the parameter
Unless indicated to the contrary, the numerical values should be understood to include numerical values which are the same when reduced to the same number of significant figures and numerical values which differ from the stated value by less than the experimental error of conventional measurement technique of the type described in the present application to determine the value.
All ranges disclosed herein are inclusive of the recited endpoint and independently of the endpoints (e.g., “between 2 grams and 10 grams, and all the intermediate values includes 2 grams, 10 grams, and all intermediate values”). The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value; they are sufficiently imprecise to include values approximating these ranges and/or values. All ranges are combinable.
As used herein, approximating language may be applied to modify any quantitative representation that may vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about” and “substantially,” may not be limited to the precise value specified, in some cases. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. The modifier “about” should also be considered as disclosing the range defined by the absolute values of the two endpoints. For example, the expression “from about 2 to about 4” also discloses the range “from 2 to 4.” The term “about” may refer to plus or minus 10% of the indicated number. For example, “about 10%” may indicate a range of 9% to 11%, and “about 1” may mean from 0.9-1.1. Other meanings of “about” may be apparent from the context, such as rounding off, so, for example “about 1” may also mean from 0.5 to 1.4. Further, the term “comprising” should be understood as having its open-ended meaning of “including,” but the term also includes the closed meaning of the term “consisting.” For example, a composition that comprises components A and B may be a composition that includes A, B, and other components, but may also be a composition made of A and B only. Any documents cited herein are incorporated by reference in their entireties for any and all purposes.
The ability to transform two-dimensional (2D) sheets into three-dimensional (3D) curved shapes enables a broad range of applications, including camouflage, soft robotics, deployable systems, biomedical devices, structures, and protection devices.
Among different techniques, kirigami that involves both cutting and folding imposes intrinsic Gaussian curvatures into the final shape, leading to conformal 3D surfaces free of overfolds or wrinkles. However, cutting typically weakens the material mechanically. Here, we report an optimal cutting approach that transforms composite cross-plies (the preform) into 3D doubly-curved laminates with optimized mechanical properties. Guided by numerical modeling, the multilayered preform can transform into desired 3D shapes with minimum cuts overlapped at the same position.
After consolidation, the weakness induced by cuts can be mitigated by the shearing forces between the plies. Our approach opens a fundamentally new paradigm to conform complex shapes of arbitrary curvatures while offering control over the local reinforcement architecture for light-weight yet high mechanical strength.
To realize shape morphing and complex curvature conforming of flat sheets, two strategies have been commonly pursued. One is to introduce inhomogeneous in-plane strains in soft elastomers via pneumatic inflation, swelling, application of electric fields and thermal activation. The other exploits kirigami and origami engineering to program the Gaussian curvatures from inextensible flat sheets. However, both approaches fail to produce 3D geometries that are both lightweight and mechanically strong as a result of stretchability, cutting and folding.
Laminated composite and hybrid materials, which are constructed from preforms consisting of layers of either high-performance fibers or minimally shear deformable films, have been extensively used in the aerospace and automotive industries, sports products and medical equipment, where the properties such as light-weight, high mechanical strength and stiffness are essential. The technology for manufacturing these materials into flat and singly curved structures is well developed. However, to achieve complex curved shapes, the necessary local deformation in the anisotropic materials often results in either shear failure, wrinkling, or significant changes in local reinforcement architecture, all of which severely limit the performance of the resulting structure.
As shown in
Recent advancement in mechanical metamaterials (e.g., kirigami) provides new strategies in programming curvature by introducing cuts into a planar sheet (shown as 104 in
To circumvent the weakness induced by the cuts, we develop, as shown in
For a given curved surface, we calculate multiple pathways to cut and unfold the discretized surface to valid 2D nets (114, 116, and 118) without self-overlapping. We then optimize the pathways to minimize the number of overlapped cuts at the same position when stacking the multilayered preform plies (118). After consolidating the folded composite plies, load sharing among plies via interlaminar shear can mitigate the effect of cuts, providing additional strength to the structure.
Our approach is validated by quasi-static mechanical testing of multiple 2D and 3D specimens with (or without) the optimized layups. The optimized specimens show significant improvement in mechanical performance compared to those without optimization, including more than 2 times increase in the tensile strength for 2D specimens and around 40% increase in the compression peak force for the hemispherical shells. First, we unfold the curved surface to valid 2D nets without self-overlapping. For a given target surface, we approximate the smooth surface using a polyhedral mesh comprising triangular facets with appropriate dimensions (
While discretizing the surface with finer facets results in better smoothness and conformability to the target surface, it will also increase the computational expense for optimization and compromise the mechanical performance since more cuts have to be introduced. In our study, we use N∈[50, 100] triangular facets to approximate the prescribed surface to obtain good conformability, reasonable computational cost and high mechanical strength. Then, we represent the polyhedral mesh using a cutting graph and employ this graph to unfold the mesh to 2D nets by calculating its minimum spanning tree (MST) using the Prim's algorithm.
Since the cutting graph elucidates the connection of the facets for the polyhedral mesh (i.e., the vertices and edges of the cutting graph correspond to the facets and edges of the mesh, respectively), the partition pathway of the polyhedral mesh can be determined by the MST of the cutting graph. For instance, by assigning a set of weights to the edges of the cutting graph, we can obtain a unique MST to specify the cutting pathway, where the edges will be cut if they do not belong to the MST.
However, the unfolding net is typically not a valid net containing multiple overlaps. To obtain a valid net without any overlap, we check if any facets of the nets are intersected with each other. Moreover, to minimize the effect of cuts on the mechanical performance of the folded composite structure, we add tabs to the cut edges of the net if no new overlap is introduced by the tabs (see design of the tab in
Our experiments show that when the tab width is large enough (i.e. Wtab≥15 mm, for the composite material considered here), the in-plane strength will not be compromised regardless of the presence of the cuts (see experimental validations in
To produce a 3D curved structure with high mechanical strength, multiple plies are typically stacked and consolidated. However, wrapping several nets with the same geometries gives rise to repeated cuts at the same location, which severely reduces the strength of the resulting structure (
To tackle this issue, we exploit load sharing by interlaminar shear among the consolidated plies and propose a universal optimization approach to guide the cutting pathway of each ply to minimize the number of overlapped cuts (
As a result, the edges of the polyhedral mesh (Emesh) and the cut edges of the i-th optimized ply (E) have the following relationships
E
1
∪E
2
∪ . . . ∪E
n
⊆E
mesh, (1)
E
i
∩E
j
=Ø,i,j=1,2, . . . ,nmax and i≠j. (2)
The maximum number of optimized plies, nmax, is determined by the number of the edges for the polyhedral mesh nedge and the number of cuts in each ply ncut through
n
max
=└n
edge
/n
cut┘, (3)
where the floor function └x┘ outputs the greatest integer less than or equal to x. For instance, the hemispherical mesh shown in
Moreover, nmax can be increased when additional tabs are added to the cut edges to further mitigate the mechanical weakness induced by the cuts. Here, we assume that the cut can be ignored where a tab with large enough dimension is added. For the hemispherical mesh shown in
The optimized plies of the hemispherical mesh are demonstrated in
To quantify the effectiveness of our model, we compare the number of overlapped cuts at each edge of the hemispherical mesh for three different designs in
The bar charts in
The principle of our approach is to optimize the cut distribution in a multi-ply stacked composite structure with minimum compromise on the mechanical strength of the structure. The in-plane strength of the laminated plies is crucial to the mechanical performance of the resulting 3D curved structures. However, it is challenging to characterize the effect of cut distribution on the in-plane properties of 3D curved structures directly.
To validate the effectiveness of our approach for different structures, we fabricate both 2D and 3D specimens and characterize their mechanical responses under different loading conditions. All samples are fabricated from Tensylon HSBD30A (DuPont™), a high modulus bidirectional laminate made from ultrahigh molecular weight polyethylene (UHMWPE) with two orthogonal layers of solid-state extruded films coated with adhesives. The material has ply thickness t=155 μm, in-plane shear modulus G12=1.5 GPa, axial tensile modulus E11=E22=44 GPa.
Compared to fiber-based materials solid-state extruded films such as Tensylon have much higher in-plane shear stiffness and can only undergo a few degrees of in-plane shear prior to failure, therefore they cannot easily be thermoformed into a hemisphere without wrinkling or tearing.
First, we conduct uniaxial tensile tests for dog bone specimens with different layups of cuts (
As seen in (
To enhance the strength of the specimens we evenly distribute the cuts between the two positions, obtaining the S4-4 specimen, which redistributes the in-plane load across each cut with 25 mm overlap between the adjacent plies and is expected to have half the tensile strength of the specimens without any cuts. Similarly, if the cuts are arranged at three positions, the resulting specimen (S3-2-3) is expected to have up to ⅝ of the tensile strength of the pristine specimen without any cuts. We can further increase the strength of the specimens by introducing tabs (see S3-2-3-tabs specimen in
To evaluate the effect of the tabs on the mechanical properties of the specimens, we compare the S3-2-3-tabs specimen, which has a tab on the top and at the bottom ply, respectively, with the S2-2-2 specimen, which has only two cuts at each position and no cut in the top and bottom plies. When the width of the tabs is large enough, the S3-2-3-tabs and S2-2-2 samples should have similar tensile strength. The specimen without cuts is tested as a reference.
In
To characterize the cut distribution on bending properties of the specimens, we then compare the load-deflection curves of the three-point bend tests for rectangular samples sharing the same cut distribution with the dog bone samples in
We now move to validate the optimized hemispherical structure. Three hemispherical specimens are manufactured according to the designs shown in
It is noted that there are no wrinkles in the hemisphere, confirming that the triangular facet size selected is not too large. Then, we conduct the compression tests (loading on top of the hemisphere) and the resultant force is reported as a function of the applied displacement in
All curves show a linear regime followed by a load drop before further stiffening, and the peak force of the optimized specimen Foptimized is remarkably larger than that of the random design, characterized by Foptimized=1.31Frandom. The optimized specimen with tabs has a even larger peak force with Ftabs=1.40Frandom, confirming that including tabs in our model improves the mechanical strength of the resulting structures.
Armed with the confidence of our optimized model in conforming hemispherical structures using non-shear deformable laminated plies, we extend our model to various curved surfaces to demonstrate its universality. For the convex surfaces with only positive Gaussian curvature, we can optimize the cutting pathways for non-developable surfaces to unfold them into a couple of single-patch 2D nets, which when folded to the prescribed 3D surfaces have minimal overlapped cuts at the same position (e.g. the hemisphere in
However, there are many examples of non-convex polyhedral meshes that do not have a valid unfolding within a single patch, owing to the existence of negative Gaussian curvatures. For example, a face guard, where light-weight and high strength are essential to protect the face from full-contact impact, has both positive and negative Gaussian curvatures (see
Unfolding this kind of surface typically results in 2D nets with local self-overlaps (see the red facets shown in
Although a few algorithms have been developed to unfold non-convex polyhedral meshes into a single patch and such algorithms can be easily integrated into our model, the additional constraint of minimizing cut overlaps hinders us from finding valid nets in a single connected patch for non-convex polyhedral surfaces.
To enhance the capability and efficiency of our model on handling structures with arbitrary curvatures, we introduce additional cuts for the non-convex surfaces to avoid the self-overlaps induced by the hyperbolic vertices. We note that the additional cuts will segment the 2D net into several patches, weakening the structure. To eliminate this weakness, we minimize the number of additional cuts by employing the greedy algorithm and add tabs to the additional cuts to enhance the mechanical performance of the structure.
Accordingly, an optimized design for a nearly arbitrary curved structure is realized. For the face guard shown in
In summary, we have introduced a universal optimization approach to morph flat composite plies towards prescribed 3D curved surfaces with optimal mechanical performance. Our algorithms minimize the number of overlapped cuts at the same position and introduce additional tabs for the applicable edges, resulting homogeneously distributed cuts in the multi-ply stacked structures.
Through 2D and 3D mechanical testing under different load conditions, we have demonstrated the validity of our approach on improving the mechanical performance of the structures by optimizing their layups. Our model is universal to a variety of curved structures and can accommodate all the existing algorithms for unfolding polyhedral meshes. The disclosed methods can be used with a variety of meshes; for instance, one can approximate the target surface using the combination of two different meshes whose edges are mutually orthogonal with each other.
By stacking the optimized designs from these meshes, the number of plies without overlapped cut can be further increased (see
Additional Disclosure
Fabrication
All structures investigated in this study are fabricated from Tensylon HSBD30A plies (DuPont™) with thickness t=155 μm, in-plane shear modulus G12=1.5 GPa, axial tensile modulus E11=E22=44 GPa and in-plane Poisson's ratio V12=0.01. The Tensylon ply is comprised of cross-plied [0/90] solid state extruded Ultra-high-molecular-weight polyethylene (UHMWPE) films with a polyolefin matrix/adhesive on one side of the film.
2D specimens. We fabricate 2 types of 2D specimens with different cut distribution (i.e., the dog bone specimens and the rectangular specimens, see their geometric parameters in
To fabricate the 2D samples, one can employ the following steps:
3D curved structures. To fabricate the 3D curved structures with optimized mechanical performance, one can first optimize the geometries of the 2D plies and then process the plies using the following steps:
The following experimental results are illustrative only and do not limit the present disclosure or the appended claims.
All mechanical testing was performed using a universal testing machine (Instron 6800 series) equipped with a 2000N load cell for the tensile and compression tests and with a 100N load cell for the bending tests. The tests were performed under displacement control at a rate of 0.05 mm/s for the tensile tests, and 0.2 mm/s for compression and bending tests, respectively.
Uniaxial tensile tests. The uniaxial tensile tests for dog bone specimens with different cut distributions are reported in
Three-point bending tests. The resultant force of three-point bending tests for the laminated plies is sensitive to the relative position of the loading pin to the cuts in the specimens.
Hence, we arrange the cuts just under the loading pin in our tests and set the distance between the supporting pins to be 50 mm (see schematic in
Compression tests for the hemispheres. To validate that the optimized 3D curved structure has better mechanical performance than the one with randomly designed cut distribution, we conduct compression tests on the hemispherical specimens with different layups (i.e., the random design, the optimized design and the optimized one with tabs). The force-displacement curves of these samples are reported in
Modeling
In this section, we provide details of our model on unfolding 3D curved surfaces to 2D nets and optimizing the geometries of 2D plies to realize prescribed 3D curved structures with optimal mechanical performance.
Unfolding 3D curved surfaces to 2D nets. To morph flat plies towards a prescribed curved surface with optimized mechanical performance, we first demonstrate the steps of unfolding curved surfaces to valid 2D nets without self-overlapping (see schematic in
Optimization of the cuts for the plies. After demonstrating the procedure of realizing valid 2D nets from a given 3D surface, we then optimize the cut distribution of each ply to minimize the number of overlapped cuts in the stacked plies. We illustrate the algorithm using a flow chart in
Note that, to realize a structure comprising more than nmax plies, one can simply repeat the optimized plies until the target thickness is reached. The optimization algorithms are implemented in Matlab.
Additional Illustrative Results
In this section, we demonstrate the capability of our model for the optimization of diverse structures, including a semi-ellipsoidal surface (
Aspects
The following Aspects are illustrative only and do not limit the scope of the present disclosure or the appended claims. Any part or parts of any one or more Aspects can be combined with any part or parts of any one or more other Aspects.
Aspect 1. A method of forming a three-dimensional (3-D) target object having a surface, the method comprising:
Aspect 2. The method of Aspect 1, further comprising stacking and consolidating the n 2-D sheets so as to form the 3-D target object, the consolidating optionally being effected by heating, vacuum, pressure, adhesive, or any combination thereof, and the consolidating optionally comprising superposing the n 2-D sheets over a mold.
Aspect 3. The method of any one of Aspects 1-2, further comprising generating the cutting graph, the cutting graph corresponding to the polyhedral mesh that is representative of the 3-D target object.
Aspect 4. The method of Aspect 3, further comprising generating the polyhedral mesh that is representative of the 3-D target object.
Aspect 5. The method of any one of Aspects 1-4, further comprising effecting placement of at least one tab on a 2-D sheet, the tab extending from an edge of the 2-D sheet so as to at least partially overlap a cut on the 2-D sheet when the n 2-D sheets are stacked and consolidated to form the 3-D target object.
Aspect 6. The method of any one of Aspects 1-5, wherein the set of cuts in at least one 2-D sheet is formed according to the minimum spanning tree (MST) of the cutting graph.
Aspect 7. The method of Aspect 6, wherein the MST is computed using Prim's algorithm and/or Kruskal's algorithm.
Aspect 8. The method of any one of Aspects 1-7, wherein the surface of the 3-D target object includes a positive Gaussian curvature.
Aspect 9. The method of any one of Aspects 1-8, wherein the surface of the 3-D target object includes a negative Gaussian curvature.
Aspect 10. The method of any one of Aspects 1-9, wherein an i-th sheet conforms to essentially the entirety of the surface of the 3-D target object.
Aspect 11. The method of any one of Aspects 1-9, wherein an i-th sheet conforms to a portion of the surface of the 3-D target object.
The disclosed methods can be performed in connection with operating a cutting device, e.g., a device that forms cuts according to the cutting graph. The disclosed methods can also be performed in connection with a 3D printing device, e.g., a device that forms sheets with or without cuts formed therein. The disclosed methods can also be performed in connection with lay-ups (i.e., applying 2D sheets to a support surface, which support surface can be curved) or even in connection with consolidation (e.g., via applying heat).
Aspect 12. A 3-D composite object having a surface, the 3-D composite object comprising:
Aspect 13. The 3-D composite object of Aspect 12, wherein at least one sheet includes a tab extending from an edge of the sheet so as to at least partially overlap a cut on the same sheet when the n sheets are stacked and consolidated to form the 3-D target object.
Aspect 14. The 3-D composite object of any one of Aspects 12-13, wherein the surface of the 3-D composite object includes a positive Gaussian curvature.
Aspect 15. The 3-D composite object of any one of Aspects 12-14, wherein the surface of the 3-D composite object includes a negative Gaussian curvature.
Aspect 16. The 3-D composite object of any one of Aspects 12-15, wherein an i-th sheet conforms to essentially the entirety of the surface of the 3-D composite object.
Aspect 17. The 3-D composite object of any one of Aspects 12-15, wherein an i-th sheet conforms to a portion of the surface of the 3-D composite object.
Such a 3-D object can be of essentially any shape. Masks, protective gear, seats, cones, body suits, armor, shoes, implants, packaging, implant wrapper, and the like are all suitable 3-D objects.
Aspect 18. A kit for forming a 3-D target object, comprising:
Aspect 19. The kit of Aspect 18, wherein the n sheets comprise a material such that when the n sheets are stacked and consolidated to form a testing dog bone having the highest cut density and minimum cut spacing (i.e., distance between cuts) of the kit of Aspect 18, the testing dog bone has a uniaxial mean strength of within 75%, within 25%, or within 10% of the uniaxial mean strength of an equivalent testing dog bone comprising n stacked and consolidated uncut sheets of the material. Without being bound to any particular theory or embodiment, one can conceptualize the dog bone as representing the weakest section (i.e., the section with the maximum number of through thickness cuts and the closest spacing between cuts in-plane) of a 3D part formed from cut 2D sheets.
Aspect 20. The kit of any one of Aspects 18-19, wherein then sheets comprise a material such that when the n sheets are consolidated and stacked to form a flat rectangular plate, a portion of the rectangular plate having a highest cut density and a minimum distance between cuts found in the kit in Aspect 18 is characterized as having a peak force as measured with a three-point bending test of within 75%, within 25%, or within 10% of the peak force of an equivalent flat rectangular plate comprising n stacked and consolidated uncut sheets of the material.
This application claims priority to and the benefit of U.S. Provisional Patent Application No. 63/318,134, “Conforming 2D Composite Sheets To 3D Curved Surfaces With Optimal Mechanical Performance” (filed Mar. 9, 2022), the entirety of which is incorporated by reference herein in its entirety for any and all purposes.
This invention was made with government support under W911NF-18-1-0327 awarded by the Army Research Laboratory-Army Research Office. The government has certain rights in the invention.
Number | Date | Country | |
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63318134 | Mar 2022 | US |