Birefringent coating method is used to determine the stress intensity factors of center cracks and cracks emanating from a circular hole in finite width composite laminates subject to uniaxial tension. Stress intensity factors are determined experimentally by applying least-square method to the relationship between isochromatic fringe order and stress intensity factor. Three types of stacking sequence are used for the specimen : $[0/\pm45/90]_{2s}$, $[\pm$45]_{4s}$, $[\pm30]_{4s}$.
In this study reinforcing effect and Poisson's ratio mismatch are investigated to conform the methodology of experiment and experimental results are compared with available theoretical results for center cracks. In case of quasi-isotropic laminate, $[0/\pm45/90]_{2s}$, experimental results have a good agreement with theoretical ones. However, for orthotropic laminates, $[\pm45]_{4s}$, $[\pm30]_{4s}$, which have larger Poisson's ratio mismatch and interlaminar stress than quasi-isotropic laminate, experimental results are much less than theoretical ones.
Large Poisson's ratio mismatch and interlaminar stress deteriorate the accuracy of the test result. Therefore for the application of birefringent coating method to composite laminates, smaller Poisson's ration mismatch between coating and laminate is recommended.
