IMPLICATIONS OF TANGENTIAL SHEAR-STRESS INDUCED FAILURE DURING TRANSVERSE LOADING OF SIC TI-6A1-4V COMPOSITES/

During transverse loading of fiber-matrix composites, the interface is subjected to both tangential shear stresses and radial stresses. Inte rface failure in several carbon/carbon-rich coated SiC/Ti-6Al-4V compo sites can occur by tangential shear stresses before the observed non-l inearity in the experimental stress-strain curve due to normal interfa ce separation. In this study, the effect of frictional sliding before normal interface separation on the stress redistribution and the stres s-strain response of SiC/Ti-6Al-4V composites was examined using finit e 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 modi fy both interface radial stress distribution and matrix hoop stress. T he 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 st ress concentration 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, respectivel y. 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.