Stress concentration in a circular hole in composite plate

A non-contact measurement method, namely electronic speckle pattern interferometer (ESPI), was used to investigate the tensile strain field of a composites plate in the presence of stress concentrations caused by a geometrical defect consisting of circular hole. ESPI uses the principle of 3D speckle interferometry to measure the deformation and contour of the measuring field with sub-micrometer accuracy. The ESPI technique clearly revealed the strain concentrations near the singularity. The experimental results are compared with the predictions of a theoretical model previously developed by Lekhnitskii's and a finite element study.