Stress analysis of fibrous composites using moiré interferometry

A sensitive moiré fringe interferometer has been developed for measuring in-plane strains in engineering materials and structures. The specific advantage of this system is that it does not have to be used in an environment isolated from external vibration. As a result, it is possible to record deformation contours with a sensitivity and spatial resolution sufficient for the accurate measurement of strains even in areas of high strain gradient. The technique has been used to investigate the behaviour of a carbon fibre reinforced plastic material under fatigue loading. The changes in strain distribution have been measured as a function of the number of cycles undergone, and have been compared with theoretical predictions of the strain distribution around a hole in an orthotropic plate.