Determining a Lower Bound Mixed Mode Failure Curve for An Interface Crack between Single Crystal Silicon and Silicone Rubber

An interface crack between single crystal silicon (SC-Si) and silicone rubber is examined. The first term of the asymptotic solution for this interface crack is derived. Mixed mode fracture tests were performed on Brazilian disk specimens at different mode mixities. Finite element analyses (FEAs) of these tests were carried out in abaqus. A cubic (anisotropic) material model is used for SC-Si. Two different material models were used for silicone rubber: A linear elastic model for the asymptotic solution and a Mooney-Rivlin (hyperelastic) model for the FEA. The FEAs showed that large deformations were relegated to a small region surrounding the crack tip. Hence, a K-dominate region exists in which linear elastic fracture mechanics (LEFM) may be used. From the FEAs of the Brazilian disk specimens, energy release rates were determined using the virtual crack closure technique (VCCT) and displacement extrapolation (DE) methods which were corroborated by J-integral values evaluated using the contour integral method. Elsewhere, it was demonstrated that properly implemented, the VCCT method may be used for interface cracks. A mixed mode failure criterion is obtained from the energy release rate data. The SC-Si failed before the interface crack propagated. Hence, the failure curve obtained in this study should be considered as a lower bound of the critical energy release rate for this material pair.