DYNAMIC MATRIX CRACKING IN FIBER-REINFORCED CERAMICS

The dynamic matrix cracking in a fiber reinforced ceramic is studied i n this paper. Crack bridging fibers are assumed to undergo viscoplasti c deformation. The viscoplastic effects are incorporated in a parametr ic bridging law in a way that increases the bridging stress under rapi d deformation and retains the classic form for rate insensitive slidin g fibers under very slow deformation. It is also assumed that the matr ix crack grows steadily according to a critical energy release rate cr iterion. An energy balance relation for dynamic steady-state matrix cr acking is derived. The dependence of dynamic matrix cracking stress on crack velocity and viscoplastic effects is determined in terms a nond imensional viscoplastic parameter. It is found that in the absence of rate effects, the matrix cracking stress is independent of crack speed . When the viscoplastic effects are present, the matrix cracking stres s increases with crack speed, becoming unbounded when the cracking spe ed reaches the Rayleigh wave speed c(R).