Residual stresses investigations in composite samples by speckle interferometry and specimen repositioning

摘要

Graphite-epoxy laminates are subjected to the "incremental hole-drilling" technique in order to investigate the residual stresses acting within each layer of the composite samples. In-plane speckle interferometry is used to measure the displacement field created by each drilling increment around the hole. Our approach features two particularities ⅰ) we rely on the precise repositioning of the samples in the optical set-up after each new boring step, performed by means of a high precision, numerically controlled milling machine in the workshop; ⅱ) for each increment, we acquire three displacement fields, along the length, the width of the samples, and at 45°, using a single symmetrical double beam illumination and a rotary stage holding the specimens. The experimental protocol is described in detail and the experimental results are presented, including a comparison with strain gages. Speckle interferometry appears as a suitable method to respond to the increasing demand for residual stress determination in composite samples.