ANALYTICAL MODELING OF THE INTERFACIAL STRESS STATE DURING PUSHOUT TESTING OF SCS-6 TI-BASED COMPOSITES

Analytical and experimental investigations were performed to determine the stress components responsible for interfacial debonding during pu shout testing. The stress distributions along the fiber/matrix interfa ce were modeled using finite element methods. Both thermal residual st resses as well as mechanical stresses were accounted for in the analys is. The analysis was performed for two SCS-6/Ti-based composite system s. The analytical results were calculated based on experimentally dete rmined fiber debonding loads obtained at different specimen thicknesse s and testing temperatures. The results of the analysis were consisten t with the experimentally observed initiation failure sites. At room t emperature, due to large thermal residual shear stresses, the maximum shear stress during thin-specimen pushout was located at the bottom fa ce away from the indenter and was found to control the initiation of i nterfacial debonding. However, in very thin specimens, the bending str esses control interfacial debonding by causing radial opening at the b ottom face. With an increase in temperature the analytical modeling sh ows that the maximum shear stress moves to the top face, due to the re laxation of the residual shear stresses. However, at high temperature the bending stresses result in failure initiation on the bottom face d ue to the softening of the matrix and the relaxation of the radial cla mping stresses.