Identification of Failure Origin Through Testing and the Weibull Risk-of-Rupture

The stress distribution in bond layers of two different thicknesses (50 μm and 200 μm) was calculated by finite element analysis for pairs of rectangular cross section metal bars bonded to each other and subjected to four point bending. These stresses were used to aid in identification of the failure origin by use of the Weibull risk-of-rupture (RR) function. By use of the stress distributions, the characteristic strength from 50 μm bond test specimens could be correlated with that for 200 μm bond test specimens when the failure was assumed to have an interfacial origin. The finite element meshes were refined twice and the ratios of characteristic strengths were recalculated and remained virtually unchanged by each of the mesh refinements. Hence, the identification of the interface as the failure origin remained consistent. Further, the use of stresses extrapolated to zero mesh size also produced the same ratios. Therefore, the RR calculations do not appear to be sensitive to the mesh sizes used for the stress calculations when the meshes are comparable or when changed in a comparable manner. The results show this method can be consistent and a useful adjunct for identification of failure origins.