A method for extracting estimates of the stress intensity factors due to Mode III loadings from photoelastic data is developed. The results are supported by a series of stress freezing photoelastic experiments conducted on circumferentially notched round bars to which torsional loads were applied yielding a pure Mode III loading condition at the notch tip. Photoelastic data were taken from slices cut from the test specimens near the notch tip and stress intensity factors obtained. Results are compared with numerical and analytical results drawn from the literature. / Master of Science