An extensive investigation of non-uniform material effects on static fracture analyses is undertaken. Included in the study are theoretical, experimental and numerical techniques of focusing attention on the nonsymmetric deformation fields around a crack tip in a non-uniform yield strength varying material. Each analysis independently shows that the material non-uniformities alter stress and strain distributions drastically and that a statically stressed crack can propagate in directions other than the crack axis direction, depending on local conditions at the crack tip. An extremely simple and versatile finite element technique called “Unimod” is developed for use in real material modelling of crack tip material elements. / Ph. D.