An optical method of measuring anisotropic deformation and necking in material testing

The mechanical properties of structural engineering materials are often highly anisotropic, particularly in wrought products. Characterisation of the material behaviour and the identification of the fracture and damage parameters of structural metals require load‐displacement data from smooth and notched tensile tests. Modern optical methods, such as 3D digital image correlation (DIC), enable full field displacement data to be collected. However, the measurement of diametral contraction in round tensile specimens is not straightforward for anisotropic materials. In this paper a method for measuring diametral contractions simultaneously in two orthogonal directions using a standard 3D DIC system in conjunction with an edge detection algorithm is described. The results show that deformation anisotropy can be readily quantified through these orthogonal diametral displacements.