AN UNSYMMETRIC END-NOTCHED FLEXURE TEST FOR INTERFACIAL FRACTURE-TOUGHNESS DETERMINATION

An unsymmetric end-notched flexure test is described and its suitabili ty for interfacial fracture toughness testing is evaluated. The test s pecimen consists of a beam-type geometry that is comprised of two mate rials, one ''top'' and one ''bottom'', with a crack at one end along t he bimaterial interface. The specimen is loaded in three-point bending : similar to a conventional end-notched flexure test. A plate theory a nalysis, modified to include the effects of transverse shear deformati on in the near tip region, is used to determine the force and moment r esultants in the specimen as well as its deformed shape. Results from this analysis are incorporated into a crack tip element approach to pr edict energy release rate and mode mixity. These analytical prediction s are verified by comparison to finite element results. It is shown th at, by varying the relative thicknesses and locations of the two mater ials, the unsymmetric end-notched flexure test can be used to determin e the fracture toughness over a reasonably wide range of mode mixities for most bimaterial interfaces. (C) 1998 Els-vier Science Ltd. All ri ghts reserved.