1,564 research outputs found
Shape Memory Alloy Nanostructures With Coupled Dynamic Thermo-Mechanical Effects
Employing the Ginzburg-Landau phase-field theory, a new coupled dynamic
thermo-mechanical 3D model has been proposed for modeling the
cubic-to-tetragonal martensitic transformations in shape memory alloy (SMA)
nanostructures. The stress-induced phase transformations and thermo-mechanical
behavior of nanostructured SMAs have been investigated. The mechanical and
thermal hysteresis phenomena, local non-uniform phase transformations and
corresponding non-uniform temperature and deformations distributions are
captured successfully using the developed model. The predicted microstructure
evolution qualitatively matches with the experimental observations. The
developed coupled dynamic model has provided a better understanding of
underlying martensitic transformation mechanisms in SMAs, as well as their
effect on the thermo-mechanical behavior of nanostructures.Comment: 8 pages, 3 figure
Numerical analysis of complex systems evolution with phase transformations at different spatial scales
This paper shows the existence of a critical dimension for finite length nanowires exhibiting shape memory effects. We give a brief survey of phase transformations, their classifications, and provide the basis of mathematical models for the phenomena involving such transformations, focusing on shape memory effects at the nanoscale. Main results are given for the dynamic of square-to-rectangular transformations modelled on the basis of the modified Ginzburg-Landau theory. The results were obtained by solving a fully coupled system of partial differential equations, accounting for the thermal field, a feature typically neglected in recent publications on the subject when microstructures of nanowires were modelled with phase-field approximations. Representative examples are shown for nanowires of length 2000nm and widths ranging from 200nm to 50nm. The observed microstructure patterns are different from the bulk situation due to the fact that interfacial energy becomes comparable at the nanoscale with the bulk energy
Effect of Aspect Ratio and Boundary Conditions in Modeling Shape Memory Alloy Nanostructures with 3D Coupled Dynamic Phase-Field Theories
The behavior of shape memory alloy (SMA) nanostructures is influenced by strain rate and temperature evolution during dynamic loading. The coupling between temperature, strain, and strain rate is essential to capture inherent thermomechanical behavior in SMAs. In this paper, we propose a new 3D phase-field model that accounts for two-way coupling between mechanical and thermal physics. We use the strain-based Ginzburg-Landau potential for cubic-to-tetragonal phase transformations. The variational formulation of the developed model is implemented in the isogeometric analysis framework to overcome numerical challenges. We have observed a complete disappearance of the out-of-plane martensitic variant in a very high aspect ratio SMA domain as well as the presence of three variants in equal portions in a low aspect ratio SMA domain. The dependence of different boundary conditions on the microstructure morphology has been examined energetically. The tensile tests on rectangular prism nanowires, using the displacement based loading, demonstrate the shape memory effect and pseudoelastic behavior. We have also observed that higher strain rates, as well as the lower aspect ratio domains, resulting in high yield stress and phase transformations occur at higher stress during dynamic axial loading
Biomimetic route to hybrid nano-Composite scaffold for tissue engineering
Hydroxyapatite-poly(vinyl) alcohol-protein composites have been prepared by a biomimetic
route at ambient conditions, aged for a fortnight at 30±2°C and given a shape in the form of
blocks by thermal cycling. The structural characterizations reveal a good control over the
morphology mainly the size and shape of the particles. Initial mechanical studies are very
encouraging. Three biocompatibility tests, i.e., hemocompatibility, cell adhesion, and toxicity
have been done from Shree Chitra Tirunal, Trivandrum and the results qualify their standards.
Samples are being sent for more biocompatibility tests. Optimization of the blocks in terms of
hydroxyapatite and polymer composition w.r.t the applications and its affect on the
mechanical strength have been initiated. Rapid prototyping and a β-tricalcium –
hydroxyapatite combination in composites are in the offing
Roadmap on semiconductor-cell biointerfaces.
This roadmap outlines the role semiconductor-based materials play in understanding the complex biophysical dynamics at multiple length scales, as well as the design and implementation of next-generation electronic, optoelectronic, and mechanical devices for biointerfaces. The roadmap emphasizes the advantages of semiconductor building blocks in interfacing, monitoring, and manipulating the activity of biological components, and discusses the possibility of using active semiconductor-cell interfaces for discovering new signaling processes in the biological world
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