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WCPM: Stanislaw Stupkiewicz (IPPT PAN)

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Diffuse interface modelling of microstructures and propagating instabilities in shape memory alloys
WCPM: Stanislaw Stupkiewicz (IPPT PAN)

Abstract:

Functional properties of shape-memory alloys (SMAs), notably the shape-memory effect and pseudoelasticity, result from the reversible martensitic phase transformation which is the main mechanism of inelastic deformation in those materials. At the micro-scale, the transformation proceeds through formation and evolution of complex martensitic microstructures. At the macro-scale, the overall response of polycrystalline SMAs often exhibits softening (up-down-up response), which leads to strain localization and inhomogeneous transformation in the form of Lüders-like bands or more complex transformation patterns, for instance, multi-prong interfaces observed in NiTi tubes under tension. Evolution of microstructure at the micro-scale and formation of transformation patterns at the macro-scale are both accompanied by nucleation, propagation and annihilation of interfaces. Spatially-resolved modelling of the corresponding phenomena can be efficiently carried out using the diffuse-interface approach. In this talk, our recent related results will be summarized. The phase-field method has been applied to model the martensitic microstructures at the micro-scale with the focus on size effects, rate-independent dissipation, and microstructure evolution during nano-indentation. In order to model strain localization and transformation patterning in polycrystalline NiTi, a macroscopic model of SMA employing a gradient enhancement has been developed along with a micromorphic-like regularization that facilitates the finite-element implementation. Finite-element simulations of representative 3D problems illustrate that the model correctly represents the loading-rate effects and complex transformation patterns in NiTi tube under tension.

Tags: WCPM

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