MEASUREMENT OF MIXED-MODE FRACTURE PARAMETERS NEAR CRACKS IN HOMOGENEOUS AND BIMATERIAL BEAMS

An investigation of deformation fields and evaluation of fracture para meters near mixed-mode cracks in homogeneous and bimaterial specimens under elastostatic conditions is undertaken. A modified edge notched f lexural geometry is proposed for testing bimaterial interface fracture toughness. The ability of the specimen in providing a fairly wide ran ge of mode mixities is demonstrated through direct optical measurement s and a simple flexural analysis. A full field optical shearing interf erometry called 'Coherent Gradient Sensing' (CGS) is used to map crack tip deformations in real time. Experimental measurements and predicti ons based on beam theory are found to be in good agreement. Also, for a large stiffness mismatch bimaterial system, the interface crack init iation toughness is evaluated as a function of the crack tip mode mixi ty.