Monitoring the strain-rate progression of an aluminium sample undergoing tensile deformation by electronic speckle-pattern interferometry (ESPI)

We have used electronic speckle-pattern interferometry (ESPI), a whole-field optical technique, to follow the evolution of the strain-rate fields induced on an aluminium sample subjected to a uniaxial tensile test. At different load stages of the test, the strain-rate at each point of the field was obtained from fringe patterns generated by an interferometer with sensitivity along both in-plane coordinates. We observed that the strain-rate fields evolved from weakly to strongly heterogeneous as the test progressed. We found that, long before reaching the maximum of the tensile force, the strain localization began at a zone of the field where the local strain-rates presented the largest values. We conclude that the strain localization onset can be efficiently detected using ESPI.