An unsymmetric double cantilever beam test for interfacial fracture toughness determination

An unsymmetric double cantilever beam test is described and its suitability for the determination of interfacial fracture toughness is evaluated. The test specimen consists of a beam-type geometry comprised of two materials, one 'top' and one 'bottom,' with a crack at one end along the bimaterial interface. The specimen is loaded in a splitting fashion similar to that of a conventional double cantilever beam test. Due to the dissimilar in-plane and out-of-plane deformations of the two legs, the load vs deflection response of the specimen is found to be nonlinear. A nonlinear plate theory is used to predict the deformations of the specimen, and these results are used in a crack tip element analysis to determine energy release rate and mode mixity. The analytical predictions are verified by comparisons to results from two-dimensional, geometrically nonlinear finite element continuum analyses for a variety of typical materials and test geometries. It is shown that, by varying the relative thicknesses of the two materials, the unsymmetric double cantilever beam test can be used on most bimaterial pairs to determine interfacial fracture toughness over a reasonably wide range of mode mixities.