The field of this application generally relates to multi-stage composites, their preparation, and their uses.
Most materials have static mechanical properties that do not adapt in response to stimuli (e.g., stress, strain, environmental conditions, and patterns of use, etc.). For example, the elastic deformation of a conventional structural material or composite usually shows an approximately constant Young's modulus: the stress increases linearly as a function of strain, until the material fails by plastic deformation or fracture. These circumstance-invariant mechanical properties can make engineering design simpler, but constrain the use of these materials. For example, on one hand, metals are stiff materials with high Young's modulus, but can fail by fatigue at low strain; and on the other hand, elastomers have low Young's modulus and stretch easily under stress, but can deform severely at high stress.
Multi-stage composites, e.g., materials that exhibit different mechanical responses under different stimuli, their preparation, and their uses are described.
Disclosed subject matter includes, in one aspect, a composite, which includes a first layer of a first material contributing to mechanical strength of the composite having a first length, and a second layer of a second material contributing to the mechanical strength of the composite having a second length, wherein the second length is greater than the first length, wherein the second length of the second layer is affixed to the first length of the first layer at both ends of the first and second lengths so that the second layer is spaced apart from the first layer.
In an aspect, a composite, which includes a first layer of a first material having a first length requiring a first load to produce each unit of incremental extension; and a second layer of a second material having a second length requiring a second load to produce each unit of incremental extension, wherein the second length is greater than the first length, wherein the second length of the second layer is affixed to the first length of the first layer at both ends of the first and second lengths so that the second layer is spaced apart from the first layer; and wherein, extension of the composite from the first length to the second length results in at least one change in the load required to produce each unit of incremental extension.
In some embodiments, the Young's modulus of the second material is same as the Young's modulus of the first material. In some other embodiments, the second load required to produce each unit of incremental extension of the second material is same as the first load required to produce each unit of incremental extension of the first material
In some embodiments, the Young's modulus of the second material is different from the Young's modulus of the first material. In some other embodiments, the second load required to produce each unit of incremental extension of the second material is different from the first load required to produce each unit of incremental extension of the first material
In some embodiments, the Young's modulus of the second material is greater than the Young's modulus of the first material. In some embodiments, the second load required to produce each unit of incremental extension of the second material is greater than the first load required to produce each unit of incremental extension of the first material.
In some embodiments, the Young's modulus of the second material is at least an order of magnitude greater than the Young's modulus of the first material. In some embodiments, the second load required to produce each unit of incremental extension of the second material is at least an order of magnitude greater than the first load required to produce each unit of incremental extension of the first material.
In some embodiments, the second layer is affixed to the first layer at at least one additional contact region so that the second layer includes at least two spaced apart sections.
In some embodiments, the at least two spaced apart sections have the same arc length.
In some embodiments, the at least two spaced apart sections have different arc lengths.
In some embodiments, the composite further includes a third layer of a third material contributing to the mechanical strength of the composite having a third length, wherein third length is greater than the second length, wherein the third length of the third layer is affixed to the first and second lengths at both ends of the first, second, and third lengths so that the third layer is spaced apart from the first and second layers.
In some embodiments, the composite further comprising, a third layer of a third material having a third length requiring a third load to produce each unit of incremental extension, wherein third length is greater than the second length, wherein the third length of the third layer is affixed to the first and second lengths at both ends of the first, second, and third lengths so that the third layer is spaced apart from the first and second layers; and wherein, extension of the composite from the first length to the third length results in at least two changes in the load required to produce each unit of incremental extension.
In some embodiments, the Young's modulus of the third material is same as the Young's modulus of the second material. In some other embodiments, the third load required to produce each unit of incremental extension of the third material is same as the second load required to produce each unit incremental extension of the second material.
In some embodiments, the Young's modulus of the third material is different from the Young's modulus of the second material. In some other embodiments, the third load required to produce each unit incremental of extension of the third material is different from the second load required to produce each unit of incremental extension of the second material.
In some embodiments, the Young's modulus of the third material is greater than the Young's modulus of the second material. In some other embodiments, the third load required to produce each unit incremental extension of the third material is greater than the second load required to produce each unit of incremental extension of the second material.
In some embodiments, the Young's modulus of the third material is at least an order of magnitude greater than the Young's modulus of the second material. In some other embodiments, the third load required to produce each unit of incremental extension of the third material is at least an order of magnitude greater than the second load required to produce each unit of incremental extension of the second material.
In some embodiments, the third layer is affixed to the second layer at at least one additional contact region so that the number of spaced apart sections in the third layer is greater than the number of spaced apart sections in the second layer.
Disclosed subject matter includes, in another aspect, a method of preparing a composite, which includes providing a first layer of a first material contributing to mechanical strength of the composite having a first length, providing a second layer of a second material contributing to the mechanical strength of the composite having a second length, wherein the second length is greater than the first length, and affixing the second length of the second layer to the first length of the first layer at both ends of the first and second lengths so that the second layer is spaced apart from the first layer.
In another aspect, a method of preparing a composite, which includes providing a first layer of a first material having a first length requiring a first load to produce each unit of incremental extension; providing a second layer of a second material having a second length, requiring a second load to produce each unit of incremental extension wherein the second length is greater than the first length; and affixing the second length of the second layer to the first length of the first layer at both ends of the first and second lengths so that the second layer is spaced apart from the first layer; and wherein, extension of the composite from the first length to the second length results in at least one change in the load required to produce each unit of incremental extension of the composite.
In some embodiments, the method further includes providing a third layer of a third material contributing to the mechanical strength of the composite having a third length, wherein third length is greater than the second length, and affixing the third length of the third layer to the first and second lengths at both ends of the first, second, and third lengths so that the third layer is spaced apart from the first and second layers. In some embodiments, the method further includes providing a third layer of a third material having a third length requiring a third load to produce each unit of incremental extension, wherein third length is greater than the second length; and affixing the third length of the third layer to the first and second lengths at both ends of the first, second, and third lengths so that the third layer is spaced apart from the first and second layers; and wherein, extension of the composite from the first length to the second length results in at least one change in the load required to produce each unit of incremental extension of the composite.
Disclosed subject matter includes, in yet another aspect, a device, which includes a first layer of a first material contributing to mechanical strength of the device having a first length, and a second layer of a second material contributing to the mechanical strength of the device having a second length, wherein the second length is greater than the first length, wherein the second length of the second layer is affixed to the first length of the first layer at both ends of the first and second lengths, wherein the second layer is spaced apart from the first layer in an unengaged state, wherein the second layer is no longer spaced apart from the first layer in an engaged state.
In yet another aspect, a device, which includes a first layer of a first material having a first length requiring a first load to produce each unit of incremental extension; and a second layer of a second material having a second length requiring a second load to produce each unit of incremental extension, wherein the second length is greater than the first length, wherein the second length of the second layer is affixed to the first length of the first layer at both ends of the first and second lengths, wherein the second layer is spaced apart from the first layer in an unengaged state, wherein the second layer is no longer spaced apart from the first layer in an engaged state.
In some embodiments, the first load required to produce each unit of incremental extension of the first layer and the second load required to produce each unit of incremental extension of the second layer have the same value
In some embodiments, the first layer contains a first active section, the second layer contains a second active section, the first and second active sections are not in contact in the unengaged state, and the first and second active sections are in contact in the engaged state.
In some embodiments, the first active section contains a first conductive strip, and the second active section contains a second conductive strip.
Disclosed subject matter includes, in another aspect, a method of using the composite including applying a first strain to the composite to stretch the first layer from its original first length to the second length of the second layer, wherein the first strain requires the application of a first load to produce each unit of incremental extension ; and applying a second strain to the to the composite to stretch the first and second layer from the second length to a length greater than the second length, wherein the second strain requires the application of a second load to produce each unit of incremental extension.
The following figures are provided for the purpose of illustration only and are not intended to be limiting.
The patent and scientific literature referred to herein establishes knowledge that is available to those of skill in the art. The issued U.S. patents, allowed applications, published foreign applications, and references, that are cited herein are hereby incorporated by reference to the same extent as if each was specifically and individually indicated to be incorporated by reference.
For convenience, certain terms employed in the specification, examples and claims are collected here. Unless defined otherwise, all technical and scientific terms used in this disclosure have the same meanings as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The initial definition provided for a group or term provided in this disclosure applies to that group or term throughout the present disclosure individually or as part of another group, unless otherwise indicated.
Circumstance-adaptive materials (CAM) can change their properties (e.g., mechanical, optical, electrical, magnetic, and biological properties, etc.) in response to use or environment (e.g., temperature, water content, electric or magnetic fields, patterns and history of use, etc.). Such materials are of interest in many technical applications, but pose a challenge in materials science and engineering. As an example of CAM in the nature, sea cucumbers can rapidly change their stiffness by secreting chemicals into their dermis that control the interactions among the collagen fibers that determine their mechanical properties.
Mechanical stress can serve as a stimulus to change mechanical properties of materials. For example, collagenous biomaterials, such as mammalian skin, arteries, ligaments, and tendons, can change their mechanical properties in response to mechanical stimuli. These biomaterials exhibit increasing modulus with applied strain, a phenomenon also referred to as strain stiffening, and the change can be reversible. This nonlinear behavior may be attributed to the crimped geometrical arrangement of the collagen fibers in elastin matrix. The stiffness of the materials increases as failure approaches. This feature can limit mechanical failure (e.g., a tear of the skin) at large extensions. Mathematical analysis has showed that strain stiffening can be beneficial for improving fault tolerance of structural materials. However, although strain stiffening has been observed among natural biomaterials, it has been difficult to achieve among synthetic materials and systems.
Embodiments of the subject matter disclosed herein can include composites that demonstrate different mechanical properties at different stages of extension, referred to herein as “multi-stage composites.” Examples of multi-staged composites include multi-layered composites that can respond to mechanical stimuli by changing their Young's modulus with changes in external strain. In one illustrative example, a multi-stage composite can include two layers of materials having different mechanical properties and physical dimensions: a shorter and elastic layer (e.g., Latex rubber) and a longer and stiff material (e.g., polyethylene (PE), Kevlar, etc.). The two layers can be affixed to one another at the opposing edges of each layer. Because of the length difference between the two layers, the longer layer spans the shorter layer and the excess length can form a spaced-apart structure over the shorter layer when the ends of the two layers are aligned and affixed together. When tensional strain is applied on the layered composite in its longitudinal direction, e.g., the composite is extended or stretched, the composite can exhibit a two distinct Young's moduli in two discrete steps. At low strains, the shorter and elastic layer dominates the mechanical properties of the composite. When strain on the composite is such that its length equals the length of the longer and stiff layer, the mechanical properties of the stiff material begin to dominate the mechanical properties of the composite. Thus, the composite can demonstrate strain stiffening behavior.
The multi-stage composites can have more than two stages of moduli. In some embodiments, the composite can possess as many steps in modulus as the number of constituent material layers. Embodiments of the disclosed subject matter can have tunable strain stiffening properties. Stepped moduli of the composites can be configured by changing the composition and the configuration of individual materials to achieve different numbers of steps in modulus, the ranges of steps, and the mechanical strength at each step. In some embodiments, when a composite has more than two steps in modulus, the materials of the composite can be layered in a hierarchical structure, resulting a smaller footprint of the composite while maintaining its performance and mechanical properties.
In some embodiments, a multi-stage composite can also possess tunable mechanical strength in response to compression as well as tension, when the compression on a coupled system is transduced to tension on the multi-stage composite. Multi-stage composites disclosed herein can be used in a wide range of situations (e.g., as sensor, actuator, etc.) In one example, an electric sensor using a multi-stage composite can monitor the amount of applied compressive strain. Applying or releasing the strain can close or open an electrical circuit, thereby reversibly turning on or off an appliance (e.g., a LED) in the circuit.
As tensile strain is applied to the two-layer composite, the shorter Latex rubber strip elongates and the longer and wavy PE strip straightens. See,
where FLatex is the calculated load to stretch the Latex strip alone, FPE is the calculated load to stretch the PE strip alone, F(x) is the calculated load to stretch the Latex-PE composite, and x is the extension. When FPE is much larger than FLatex (e.g., an order of magnitude larger), the FLatex can become negligible comparing to FPE. Note that the sum of the stress values of the two components of a composite can be different from the stress value of the composite. For example,
Here, σLatex is the stress of Latex, and σPE is the stress of PE in tension, and σ(x) is the stress of the composite. ALatex is the cross sectional area (width×thickness) of Latex, and APE is the cross sectional area of PE.
The threshold extensions can be adjusted so that the mechanical properties of the multi-stage composites are tunable.
The arched structure of the longer layer in a multi-stage composite can potentially increase the footprint (e.g., size/volume) of the composite. The increased footprint can sometimes limit applications of multi-staged composites. In some embodiments, the size/volume of a stepped-modulus composite can be reduced by increasing the points of attachment between the two layers (e.g., points/lines/regions of attachment). Composites with smaller amplitudes of waves can be integrated more effectively into smaller volumes, while maintaining their mechanical properties and performances. Assuming a sinusoidal shape for the longer and stiffer component, the amplitude of the curve can decrease as the wavelength decreases while maintaining the arc length. As illustrated in
In one or more embodiments, the spacing between contact points is substantially the same. In other embodiments, the spacing between segments can differ. Experiments have also shown that multi-stage composites can maintain their stepped-modulus features regardless of the arc length of each segment (wave) defined between two contact points/lines/regions.
In the embodiments above, layers can be attached along attachment lines which are generally perpendicular to the extension direction of the composite. In some other embodiments, the two layers can be attached along attachment lines which are not perpendicular to the longitude direction of the composite. For example, as illustrated by
The multi-stage composites in the disclosed subject matter are not limited to two stages or two layers.
Referring to
where FLatex is the calculated load to stretch the Latex strip alone, FPE is the calculated load to stretch the PE strip alone, F Kevlar is the calculated load to stretch the Kevlar strip alone, and F(x) is the calculated load to stretch the Latex-PE-Kevlar composite, and x is the extension. As in a two-component composite discussed earlier, the sum of the stress values of the three components of a composite can be different from the stress value of the composite.
Still referring to
Similar to a two-stage composite as illustrated in
The stepped mechanical strength of multi-stage composites is not limited to be only responding to tensional strains but can be responding to other types of mechanical stimuli. In the example illustrated in
The multi-stage composites in the disclosed subject matter can have many applications across a wide range of fields. In one aspect, multi-stage composites can allow engineered or configurable mechanical properties. Multi-stage composites can be manufactured with a variety of materials, such as plastics, fabrics, paper, and foils, etc. Combinations of these materials with different sizes and properties can produce a composite with dynamic mechanical properties. The dynamic properties of multi-stage composites can be engineered to suit the requirements for specific applications (e.g. sensors, actuators, etc.). In another aspect, multi-stage composites can serve as bio-inspired materials. Examples of natural materials with an increasing modulus with applied strain can include skin, arteries, ligaments, and tendons, etc. The strain stiffening properties can manifest a J-shaped stress-strain curve. These bio-inspired composites can mimic the mechanical properties of natural materials. In yet another aspect, multi-stage composites can be used in non-linear systems. The multi-stage composites are analogous to shear-thickening fluids although the mechanical strength of the composites increases with the absolute amount of strain rather than the strain rate. Dilatants, for example, have been used as an energy-absorbent medium in protective clothing. Likewise, the multi-stage composites can allow the cloth wearer to have a normal range of motion and yet resist large strain that may cause injury. They can be used to assist rehabilitation and/or prevent joint injury for patients and athletes. In yet another aspect, multi-stage composites can work as mechanical diodes. The multi-stage composites can have at least two distinct regions of mechanical strength. The characteristic is analogous to current rectification in electrical diodes. For example, small changes in strain, near the threshold strain, can lead to large changes in modulus. This asymmetric characteristic could be useful in constructing complex materials that mimic electronic devices, like transistors or switches.
For example, a multi-stage composite's feature of spacing apart two layers in a unstimulated state and contacting the two layers in a stimulated state can be used for a variety of applications, such as closing a switch or completing a circuit. In some embodiments, electrical switches sensing and responding to multiple stages of extension can be manufactured using multi-stage composites. In the example illustrated in
In another example illustrated in
The geometries of stepped modulus composites are not limited to one-dimensional structures and can be designed to respond to mechanical stimuli in different directions.
Those skilled in the art would readily appreciate that all parameters and configurations described herein are meant to be exemplary and that actual parameters and configurations will depend upon the specific application for which the systems and methods of the present invention are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that the invention may be practiced otherwise than as specifically described. The present invention is directed to each individual feature, system, or method described herein. In addition, any combination of two or more such features, systems or methods, if such features, systems or methods are not mutually inconsistent, is included within the scope of the present invention.
This patent application claims the benefit of the earlier filing date of U.S. Patent Application No. 61/933,510, filed on Jan. 30, 2014, the contents of which are incorporated by reference herein in its entirety.
This invention was made with government support under Grant No. W911NF-09-1-0476 awarded by the US Army Research Office and Grant No. N00014-10-1-0942 awarded by Office of Naval Research. The government has certain rights in this invention.
Filing Document | Filing Date | Country | Kind |
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PCT/US15/13291 | 1/28/2015 | WO | 00 |
Number | Date | Country | |
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61933510 | Jan 2014 | US |