Confocal laser scanning photoelasticity:: Improvement of precision for quantitative photoelastic studies on model composite materials

Photoelastic studies on model composite materials with different model materials and load applications have been performed to understand the various failure mechanisms in real composites. Optical investigations of the stress fields have been conducted using a polarising, confocal laser scanning microscope (Zeiss LSM 410, Zeiss, Jena, Germany), where the phase of the isochromatic fringes has been determined from the data. Two different methods are presented to improve the quantitative evaluation of the isochromatic phase. By combining manual and automatic evaluation of fringes, even samples with a high stress gradient can be analysed. A method has been developed for the correction of the integrated through-thickness birefringence, in the case of rotationally symmetric stress fields. This technique permits the inverse calculation of stress at various depths in the sample, in particular in the case of a nonlinear dependence of optical birefringence on stress. Both methods are demonstrated in the evaluation of tensile tests on multifibre model samples (glass fibres in polycarbonate).