PREDICTED EFFECTS OF INTERFACIAL ROUGHNESS ON THE BEHAVIOR OF SELECTED CERAMIC COMPOSITES

Potential effects of interfacial roughness in ceramic composites mere studied using a model that included the progressively increasing contr ibution of roughness with relative fiber/matrix displacement during de bonding of the fiber/matrix interface. A parametric approach was used to study interfacial roughness in conjunction with other parameters su ch as the strength, radius, and volume fraction of the fiber, The prog ressive roughness contribution during initial fiber/matrix sliding cau sed a high effective coefficient of friction, as well as an increased clamping stress, which led to rapidly changing friction with increasin g debond length. Calculated effects implied a potentially significant contribution to the behavior of real composite systems and the necessi ty for explicit consideration in the interpretation of experimental da ta to understand composite behavior correctly. In a tension test, the Poisson's contraction of the fiber may negate the effects of roughness , allowing an ''effective constant shear stress'' (tau) approximation, This was evaluated using a piecewise linear approximation to the prog ressive roughness model in an analysis of composite stress-strain beha vior; for the Nicalon/SiC system, the effective tau value was lower th an the values that would be obtained from fiber pushout tests and/or m atrix crack spacings.