Microstructure-based finite deformation modelling of super-elastic NiTi shape memory alloy considering various inelastic mechanisms

Abstract

In this study the mechanisms of transformation-induced plasticity (TRIP), detwinning-induced plasticity (DIP), and accumulation of residual martensite, are incorporated into a finite-deformation crystal plasticity model of NiTi SMA for the first time. The constitutive model is constructed at the single-crystal scale and also includes phase transformation and detwinning mechanisms. Using a proposed Helmholtz free energy, the driving forces for inelastic mechanisms are derived within the framework of thermodynamics. The constitutive model has been implemented in the Abaqus/Explicit finite-element program, using VUMAT subroutine to simulate a polycrystalline material. Considering various orientations for crystals, the effect of texture on tension-compression asymmetry is investigated. It is shown that different textures may cause stiffer, softer, or similar response in compression compared to tension. Due to the incorporation of the effect of residual martensite, the model provides accurate predictions of experimentally measured residual strain. The incorporation of the aforementioned inelastic deformation mechanisms is shown to accurately capture the key features related to cyclic loading. Finally, the effect of detwinning-induced plasticity in compressive cyclic loading of NiTi SMA is investigated. In strain-controlled cyclic compression-unloading tests DIP leads to a less negative peak stress and a more negative residual strain following several loading cycles.

A new constitutive model for permanent deformation of blood clots with application to simulation of aspiration thrombectomy

“…Therefore, the necessary conditions for 𝜆 ̇𝑝 to satisfy the second law of thermodynamics (equation ( 12)) are (Ebrahimi et al, 2021):…”

A new constitutive model for permanent deformation of blood clots with application to simulation of aspiration thrombectomy

“…Therefore, the necessary conditions for ̇ to satisfy the second law of thermodynamics (equation ( 12)) are (Ebrahimi et al, 2021):…”