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 (SCF). These
approaches are applied for 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 a 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 shows 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.