1993 Volume 42 Issue 472 Pages 59-64
Behavior of delamination crack growth in a carbon fiber reinforced plastic (CFRP) was investigated under static creep, two step creep and high temperature fatigue at 473K (200°C) using DCB specimens. The material was a unidirectional laminate, APC-2, which consists of carbon fibers, AS4, and a thermoplastic polymer, poly-ether-ether-ketone (PEEK). In the static and two step creep tests, the crack propagation rate against time, dl/dt, was governed by the energy release rate, G, regardless of the stress change. The crack propagation in high temperature fatigue was classified into time-dependent and cycle-dependent ones. In the former, the propagation rate against time, dl/dt, was correlated well with the energy release rate, G, and the relationship coincided with that in static creep (dl/dt=CcGmc; Cc and mc are material constants.). In the latter, the rate against load cycles, dl/dN, was controlled by the energy release rate range, ΔG(dl/dN=CfΔGmf; Cf and mf are material constants.). These imply that the crack grew under the small scale creep and small scale yielding condition, respectively. The condition of transition from the time-dependent crack propagation to the cycle-dependent one was given by a relationship, Cc∫t10Gmcdt=CfΔGmf, where t1 is the cycle period. The fracture surface in the time-dependent fatigue was characterized by the interface cracking between fibers and matrices. On the other hand, the matrix cracking near the fiber dominated in the cycle-dependent fatigue.
