Failure Characteristics of 6061/Al₂O₃/15p and 2014/Al₂O₃/15p Composites as a Function of Loading Rate

The effects of loading rate on the toughness and fracture mechanisms of two cast 6061/Al₂O₃/15p and 2014/Al₂O₃/15p composites under the as-worked (AW) and AW + T6 conditions have been examined. The quasistatic bending and high-rate impact tests were conducted over strain rates from 5 × 10^-4 to 1 × 10³ s^-1 using screw-driven or servohydraulic high-rate systems. The results showed that the peak load P_max, specimen deflection d, specimen lateral expansion fraction Δw, crack initiation energy E_i, propagation energy E_p, total fracture energy E_t, and deformation zone all tended to increase with increasing strain rate. Under quasistatic loading, the composites failed predominantly by matrix/reinforcement interface decohesion. As the loading rate increased, reinforcement failure became the major failure mechanism. Differences in the effect of matrix microstructure and stress state on the fracture properties also are discussed. In comparing the fracture modes in the AW and AW + T6 specimens, the latter showed a higher tendency toward particle cracking. Based on mechanical data, the degree of specimen deflection and expansion and fracture modes, the AW composites exhibited a higher strain-rate dependence. The T6 specimens, due to their intrinsicly more brittle nature, appeared to be less influenced by loading rate over the strain-rate range examined.