64 research outputs found
Entangled single-wire NiTi material: a porous metal with tunable superelastic and shape memory properties
NiTi 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
mesostructure is 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 ( 25 -
40), 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.Comment: 31 pages, 10 figures, submitted to Acta Materiali
3-D image-based numerical computations of snow permeability: links to specific surface area, density, and microstructural anisotropy
We used three-dimensional (3-D) images of snow microstructure to carry out numerical estimations of the full tensor of the intrinsic permeability of snow (<b>K</b>). This study was performed on 35 snow samples, spanning a wide range of seasonal snow types. For several snow samples, a significant anisotropy of permeability was detected and is consistent with that observed for the effective thermal conductivity obtained from the same samples. The anisotropy coefficient, defined as the ratio of the vertical over the horizontal components of <b>K</b>, ranges from 0.74 for a sample of decomposing precipitation particles collected in the field to 1.66 for a depth hoar specimen. Because the permeability is related to a characteristic length, we introduced a dimensionless tensor <b>K</b>*=<b>K</b>/<i>r</i><sub>es</sub><sup>2</sup>, where the equivalent sphere radius of ice grains (<i>r</i><sub>es</sub>) is computed from the specific surface area of snow (SSA) and the ice density (&rho;<sub>i</sub>) as follows: <i>r</i><sub>es</sub>=3/(SSA&times;&rho;<sub>i</sub>. We define <i>K</i> and <i>K</i>* as the average of the diagonal components of <b>K</b> and <b>K</b>*, respectively. The 35 values of <i>K</i>* were fitted to snow density (&rho;<sub>s</sub>) and provide the following regression: <i>K</i> = (3.0 &pm; 0.3) <i>r</i><sub>es</sub><sup>2</sup> exp((&minus;0.0130 &pm; 0.0003)&rho;<sub>s</sub>). We noted that the anisotropy of permeability does not affect significantly the proposed equation. This regression curve was applied to several independent datasets from the literature and compared to other existing regression curves or analytical models. The results show that it is probably the best currently available simple relationship linking the average value of permeability, <i>K</i>, to snow density and specific surface area
Multiscale modeling of the hygro-mechanical behavior of non-symmetric sandwich composite made of bio-based material
International audienc
the temperature-gradient metamorphism of snow: toward an evaluation of 3d numerical models by time-lapse images acquired under x-ray tomography?
International audienc
Mechanics of entangled single-wire materials : from above ½ in compression to below 0 in tension?
International audienc
Mechanics of entangled single-wire materials : from above ½ in compression to below 0 in tension
International audienc
Mécanique des milieux enchevêtrés monofilamentaires
National audienc
Moisture induced swelling properties of natural cellulose fibres characterized by synchrotron x-ray computed tomography
International audienc
Synchrotron radiation microtomography applied to investigation of paper
International audienc
Mechanics of entangled single-wire materials : can Poisson’s function be larger than ½ or less than 0 ?
International audienc
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