A technique for obtaining values of the stress intensity factor from photoelastic data for three dimensional cracked body problems is described. The stress intensity determination is accomplished without resorting to stress separation methods through employing an expression for the maximum in-plane shearing stress consisting of a singular term which is related to the stress intensity factor and a constant term which is related to the regular stress field. The technique itself identifies the zone dominated by the singular stresses. The effects of using artificial cracks and a model material which exhibits a Poisson's ratio v = 0.5 are assessed. The application of the technique to a variety of technologically important three dimensional problems is illustrated for Mode I loading and combined Mode I - Mode II loading. The major advantages and limitations of the technique are discussed. Replications of identical test geometries indicate a scatter of the stress intensity factor determination of less than ± 5%. It is concluded that the method is a valid means for the independent determination of values of the stress intensity factor. / Ph. D.