An unsymmetric end-notched flexure test for interfacial fracture toughness determination

An unsymmetric end-notched flexure test is described and its suitability for interfacial fracture toughness testing is evaluated. The test specimen consists of a beam-type geometry that is comprised of two materials, one "top" and one "bottom", with a crack at one end along the bimaterial interface. The specimen is loaded in three-point bending: similar to a conventional end-notched flexure test. A plate theory analysis, modified to include the effects of transverse shear deformation in the near tip region, is used to determine the force and moment resultants in the specimen as well as its deformed shape. Results from this analysis are incorporated into a crack tip element approach to predict energy release rate and mode mixity. These analytical predictions are verified by comparison to finite element results. It is shown that, by varying the relative thicknesses and locations of the two materials, the unsymmetric end-notched flexure test can be used to determine the fracture toughness over a reasonably wide range of mode mixities for most bimaterial interfaces. (C) 1998 Els-vier Science Ltd. All rights reserved.