Implications of tangential shear stress induced failure during transverse loading of SiC/Ti-6Al-4V composites

During transverse loading of fiber-matrix composites, the interface is subjected to both tangential shear stresses and radial stresses. Interface failure in several carbon/carbon-rich coated SiC/Ti-6Al-4V composites can occur by tangential shear stresses before the observed non-linearity in the experimental stress-strain curve due to normal interface separation. In this study, the effect of frictional sliding before normal interface separation on the stress redistribution and the stress-strain response of SiC/Ti-6Al-4V composites was examined using finite element analysis. The interface was modeled by contact elements with varying coefficients of friction, representing two different types of carbon/carbon-rich composite interfaces. Results indicate that stress redistribution due to tangential shear sliding may significantly modify both interface radial stress distribution and matrix hoop stress. The matrix equivalent stresses, however, are not significantly affected by tangential shear sliding until normal interface separation occurs. A methodology and pertinent plots are provided for determining the stress concentation factor and the normal bond strength of an interface where tangential shear sliding is known to occur. Using this approach, the normal bond strengths for the Trimarc 1/Ti-6Al-4V and the SCS-6/Ti-6Al-4V interfaces were estimated as 40 MPa and 145 MPa, respectively. These values are significantly higher than those calculated without considering frictional sliding. The progression of interface failure under transverse loading and its effects on the stress-strain response is also discussed.