Abstract:We study the force vs extension behaviour of a helical spring made of a thin
torsionally-stiff anisotropic elastic rod. Our focus is on springs of very low
helical pitch. For certain parameters of the problem such a spring is found not
to unwind when pulled but rather to form hockles that pop-out one by one and
lead to a highly non-monotonic force-extension curve. Between abrupt loop
pop-outs this curve is well described by the planar elastica whose relevant
solutions are classified. Our results may be relevan… Show more
“…Helical microstructures 99 also possess the ‘J-shaped’ stress–strain behavior 100-104 . For a helical ribbon, as shown in Figure 5a, Pham et al 105 gave an analytical expression that captures the non-linear mechanics response under the conditions that the ratio of t / w ≪ 1 and L/ w ≪ 1, i.e.,…”
A variety of natural biological tissues (e.g., skin, ligaments, spider silk, blood vessel) exhibit ‘J-shaped’ stress-strain behavior, thereby combining soft, compliant mechanics and large levels of stretchability, with a natural ‘strain-limiting’ mechanism to prevent damage from excessive strain. Synthetic materials with similar stress-strain behaviors have potential utility in many promising applications, such as tissue engineering (to reproduce the nonlinear mechanical properties of real biological tissues) and biomedical devices (to enable natural, comfortable integration of stretchable electronics with biological tissues/organs). Recent advances in this field encompass developments of novel material/structure concepts, fabrication approaches, and unique device applications. This review highlights five representative strategies, including designs that involve open network, wavy and wrinkled morphoologies, helical layouts, kirigami and origami constructs, and textile formats. Discussions focus on the underlying ideas, the fabrication/assembly routes, and the microstructure-property relationships that are essential for optimization of the desired ‘J-shaped’ stress-strain responses. Demonstration applications provide examples of the use of these designs in deformable electronics and biomedical devices that offer soft, compliant mechanics but with inherent robustness against damage from excessive deformation. We conclude with some perspectives on challenges and opportunities for future research.
“…Helical microstructures 99 also possess the ‘J-shaped’ stress–strain behavior 100-104 . For a helical ribbon, as shown in Figure 5a, Pham et al 105 gave an analytical expression that captures the non-linear mechanics response under the conditions that the ratio of t / w ≪ 1 and L/ w ≪ 1, i.e.,…”
A variety of natural biological tissues (e.g., skin, ligaments, spider silk, blood vessel) exhibit ‘J-shaped’ stress-strain behavior, thereby combining soft, compliant mechanics and large levels of stretchability, with a natural ‘strain-limiting’ mechanism to prevent damage from excessive strain. Synthetic materials with similar stress-strain behaviors have potential utility in many promising applications, such as tissue engineering (to reproduce the nonlinear mechanical properties of real biological tissues) and biomedical devices (to enable natural, comfortable integration of stretchable electronics with biological tissues/organs). Recent advances in this field encompass developments of novel material/structure concepts, fabrication approaches, and unique device applications. This review highlights five representative strategies, including designs that involve open network, wavy and wrinkled morphoologies, helical layouts, kirigami and origami constructs, and textile formats. Discussions focus on the underlying ideas, the fabrication/assembly routes, and the microstructure-property relationships that are essential for optimization of the desired ‘J-shaped’ stress-strain responses. Demonstration applications provide examples of the use of these designs in deformable electronics and biomedical devices that offer soft, compliant mechanics but with inherent robustness against damage from excessive deformation. We conclude with some perspectives on challenges and opportunities for future research.
“…However, an inextensible strip model is known to have singular issues that could be problematic for numerical simulations [31,32]. On the other hand, anisotropic rod models have been successfully applied to study the shape of a narrow Möbius strip [33], the cascade unlooping of helical strips [34], and bifurcations of buckled narrow strips [31]. In this work, we use the anisotropic rod theory to model elastic strip networks.…”
Section: Geometry Of a Bigon And A Bigon Ringmentioning
We propose a numerical framework to study mechanics of elastic networks that are made of thin strips. Each strip is modeled as a Kirchhoff rod, and the entire strip network is formulated as a twopoint boundary value problem (BVP) that can be solved by a general-purpose BVP solver. We first study the buckling behavior of a bigon, which consists of two strips initially straight and deformed so as to intersect with each other through a fixed angle at the two ends. Numerical results match with experimental observations in that the intersection angle and aspect ratio of the strip's cross section contribute to make a bigon buckle out of plane. Then we study a bigon ring that is composed of a series of bigons to form a loop. A bigon ring is observed to be multistable, depending on the intersection angle, number of bigon cells, and the anisotropy of the strip's cross section. We find both experimentally and numerically that a bigon ring can fold into a multiply-covered loop, which is similar to the folding of a bandsaw blade. Finally we explore the static equilibria and bifurcations of a 6-bigon ring, and find several families of equilibrium shapes. Our numerical framework captures the experimental configurations of a bigon ring well and further reveals interesting connections among various states. Our framework can be applied to study general elastic strip networks that may contain flexible joints, naturally curved strips of different lengths, etc. The folding and multistable behaviors of a bigon ring may inspire the design of novel deployable and morphable structures.
“…This kind of structures has been widely studied in the nonlinear framework 2,9,16 since they suffer from geometrical instabilities that can lead to a sudden loss of stiffness as well as extreme deformation shapes, as shown in Figure 1. Moreover their various applications in the aerospace field 11,12 , but also in biophysics, biomechanics or even in micro or nanomechanics 15 are as many motivations to develop robust models 1,14 .…”
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