Determination of interfacial properties from observations of progressive fiber debonding and pullout

The characterization of the fiber/matrix interface or interphase region is important in accurately modeling the behavior of composites. Pushout and pullout testing on single fibers are the two primary methods for examining interfacial properties such as the coefficient of friction, residual stresses, interfacial strength or toughness, and the fiber roughness. In this study, single fiber pullout tests were performed on silicon carbide fibers (SCS-2) embedded in a barium borosilicate glass matrix. The samples were made by first passing the silicon carbide fibers through a flame and then sandwiching them between two pieces of glass. The sandwich was then heated in air for 75 min at 850°C under slight pressure. Relations between the length of the debond and the applied load (during progressive debonding) and between the embedded length and the applied load during pullout were determined from the pullout tests. The transparency of the glass allowed the propagation of the debond crack to be observed using an optical microscope. The roughness of the interface caused significant wearing during pullout.