Nondestructive evaluation of fiber-reinforced polymer composites by an all-fiber-optic phase-shifting electronic speckle pattern interferometer

In this paper, we present the development details of an all fiber optic phase shifting electronic speckle pattern interferometer (ESPI) and its applications in non-destructive evaluation (NDE) of glass fiber reinforced plastics (GFRP). Laminates made of GFRP are studied using the developed ESPI system in its shear configuration. This provides a full-field, non-contact method for NDE, and also observation of surface strains which are proportional to displacement derivatives. Since defects in objects usually induce strain concentrations, shear ESPI reveals defects by identifying anomalies in strain concentration. Experiments have been carried out for NDE of unidirectional GFRP specimens at different fiber orientations and having programmed defects. The experimental results are compared with the theoretical predictions.