Entangled single-wire NiTi material: A porous metal with tunable superelastic and shape memory properties

Abstract

International audienceNiTi porous materials with unprecedented superelasticity and shape memory were manufactured by self-entangling, compacting and heat treating NiTi wires. The versatile processing route used here allows to produce entanglements of either superelastic or ferroelastic wires with tunable mesostructures. Three dimensional (3D) X-ray microtomography shows that the entanglement mesostructures are homogeneous and isotropic. The thermomechanical compressive behavior of the entanglements was studied using optical measurements of the local strain field. At all relative densities investigated here (similar to 26-36%), entanglements with superelastic wires exhibit remarkable macroscale superelasticity, even after compressions up to 25%, large damping capacity, discrete memory effect and weak strain-rate and temperature dependencies. Entanglements with ferroelastic wires resemble standard elastoplastic fibrous systems with pronounced residual strain after unloading. However, a full recovery is obtained by heating the samples, demonstrating a large shape memory effect at least up to 16% strain

Size-dependent mechanical behavior and boundary layer effects in entangled metallic wire material systems

“…It must be noticed that rather than the relative density, the porosity is sometimes used as a defining parameter, because of the similarity between EMWM and porous materials [2,3,17]. Ma et al [18] have studied the effects of the wire diameter, material, helix dimension, and relative density on the compressive properties of EMWM.…”

“…Entangled metallic wire material (EMWM) [1][2][3] (also called metal mesh [4][5][6] in earlier literature) is a form of porous material made from tangled metallic helix wires. Entangled metallic wire structures are manufactured via a process of wire drawing, weaving, and compression molding.…”

Geometrically exact beam elements and smooth contact schemes for the modeling of fiber-based materials and structures

“…It is assumed that the nodal primary degrees of freedom describing the nodal triads Λ i (ψ i ) are given by nodal rotation vectors ψ i ∈ 3 for i = 1, 2, 3. Additionally, the nodal primary degrees of freedom d 1 ,t 1 ,d 2 ,d 2 at the element boundary nodes 1 and 2 are employed in order to define the Hermite centerline interpolation (4). Here and in the following, nodal primary variables of the finite element discretization will be marked by a hat(.).…”

“…Highly slender fiber-or rod-like components represent essential constituents of mechanical systems in countless fields of application and scientific disciplines such as mechanical engineering, biomedical engineering, materials science and bio-or molecular physics. Examples are high-tensile industrial webbings, fiber-reinforced composite materials, fibrous materials with tailored porosity, synthetic polymer materials or also cellulose fibers determining the characteristics of paper [1,2,3,4,5]. On entirely different time and length scales, such slender components are relevant when analyzing the supercoiling process of DNA strands, the characteristics of carbon nanotubes or the Brownian dynamics within the cytoskeleton of biological cells [6,7,8].…”

Packing loops into annular cavities

“…The structures formed in these circumstances have a high surface/bulk ratio, and they extend the field of evolving non-equilibrium cellular systems composed of interacting domains separated by thin boundaries endowed with line energy [5]. New results on this subject may also be of interest in the study of shape memory materials using elastoplastic alloy wires [6] among others [7].…”