Toughness and fatigue of encapsulation-processed silicon carbide-polymer matrix particulate composites

Abstract

A new process for composite fabrication was developed which improves distribution of the particulate reinforcing phase by polymer encapsulation of the particulate prior to consolidation. The effect of such processing on the fatigue-crack propagation and fracture toughness behaviour of particulate thermoplastic composites was investigated. Composites of several particulate size ranges were fabricated into disc-shaped, compact tension specimens and tested under cyclic and monotonie loading conditions. For comparison, a composite was also fabricated using a standard casting technique. The observed fatigue-crack growth rates spanned three orders of magnitude (10−11 to 10−9 m per cycle) over an applied stress intensity range, ΔK, of 0.3 to 1.1 MPa m1/2. The measured fracture toughness values ranged from 0.69 to 2.95 MPa m1/2. Comparison of the two processing techniques indicated that encapsulation processing increased the fracture toughness of the composite by approximately 33%; however, the fatigue-crack growth behaviour was unaffected. In addition, a trend of increasing crack growth resistance (toughness) with increasing reinforcement particle size was observed. These results are discussed in the light of crack shielding and bridging models for composite toughening.