Finite element analysis of stress concentration in pseudoelastic thin sheets considering phase transformation and plasticity

Abstract

Shape memory alloys (SMAs) are unique materials widely used in actuators, intelligent structures, and mechanical vibration absorbers due to their distinctive properties. Designing SMA mechanical components can present a challenge due to the presence of complex stress distributions field promoted by the combination of geometric discontinuities, such as holes or notches, and phase transformations that can induce stress redistribution. The use of stress concentration factors (K_t) is a traditional approach that provides a simple method for design calculations of SMA components. This study investigates the stress concentration present in 1–mm-thick pseudoelastic sheets with a hole and evaluates the stress concentration factors for this geometry. The effects of different hole diameters (3, 6, 9, and 12 mm) are investigated using a finite element model that incorporates pseudoelasticity and plasticity to evaluate the stresses, strains, and phase transformation fields. Experimental data, obtained from standardized specimens with identical heat treatment but different cyclic training strains (6.5 and 10%), are used to calibrate the constitutive model parameters. Numerical results are compared to experimental data showing good agreement. Stress concentration analysis reveals that, while during the initial loading phase K_t values are similar to the elastic analytical value, for higher stress levels both phase transformation and plasticity affect the value of K_t which presents a variation throughout the loading history. Finally, the training process was investigated showing that it can affect hysteresis and K_t values. Results indicate that the proposed methodology for estimating K_t values in SMAs can be a useful tool to assist the design of pseudoelastic components.