Quality of the strain state in simple shear testing using field measurement techniques

Abstract

Shear testing holds a peculiar place in sheet metal characterization for multiple reasons. Indeed, as opposed to tension or bi-axial expansion, the principal strains of such a deformation change their direction, non-linearly, as a test proceeds. It is, in general, also impossible for an experimental setup to reproduce theoretical conditions. The kinematics assumptions are therefore not verified in absolute, but satisfied up to a certain level that often remains subjective. Fortunately, field measurement methods provide comprehensive data that can be used for assessing and improving experimental processing. In this work, digital image correlation is applied to different types of shear testing performed on a dual phase steel. Results are used to construct quantitative estimators to assess the quality of measurement as well as to decrease the number and weight of assumptions. A method is also proposed to separate the measured kinematics into the expected theoretical ones and the unwanted experimental deviations. It is quantitatively shown that, for the considered material and sample types, translational simple shear testing achieves kinematics that are closer to theory than pseudo-simple shear testing. The other major finding of this work is a method to identify shear strains independently of experimental biases.