Analysis of stress concentration in pseudoelastic plates using digital image correlation (DIC) and finite element method

Abstract

Shape Memory Alloys (SMAs) are materials known for their thermomechanical coupling associated to phase transformation processes. When subjected to stresses, SMAs exhibit nonlinear characteristics, necessitating special methodologies to assess their performance and structural integrity. The design of mechanical components with geometric discontinuities, such as notches and holes, has traditionally been addressed through simplified mechanical design methods incorporating stress concentration factors (SCFs). These approaches are applied under both static and cyclic mechanical or thermal loading conditions. The presence of plastic deformations introduces stress/strain redistribution and nonlinearities effects such as plasticity. In this work the stress concentration in SMA pseudoelastic thin plates with holes is investigated through numerical simulations and experimental tests. The numerical model is based on finite elements method using a SMA constitutive model to represent the pseudoelastic behavior and plasticity is calibrated from experimental results obtained from tension tests with the Digital Image Correlation (DIC) method. The numerical results present the effect of stresses and martensitic volume fractions and the strain decomposition results considering elasticity, phase transformation and plasticity. An experimental-numerical calibration is performed with good agreement. The DIC results present a Lüders type strain related to the preferential transformation pattern. The stress concentration factors are calculated from numerical results and show a variation of its value according to the stage of phase transformation and plasticity. The study presents a proposal of a method to consider the effect of geometry and material properties and load history on the design of mechanical components.