Effect of rubber particle-plastic zone interactions on fatigue crack propagation behaviour of rubber-modified epoxy polymers

Abstract

The purpose of this letter is to report a novel observation on the effect of rubber particle-plastic zone interactions on the transition point in the fatigue crack propagation (FCP) behaviour of rubber-modified epoxy polymers. This observation provides useful information relevant to the modelling of FCP behaviour of rubber-modified thermoset polymers. The findings reported here are the preliminary results from more detailed studies on the effect of rubber particle size and volume fraction on the FCP resistance of rubber-modified epoxy polymers [1]. McGarry and co-workers [2, 3] were among the first to show that the poor fracture resistance of epoxy polymers could be enhanced by the incorporation of a dispersed rubbery phase. Since their initial investigations, several studies [4-10] have provided a detailed description of the deformation micromechanisms responsible for the increase in fracture toughness of rubber-modified epoxy polymers. The most commonly observed among these mechanisms, as shown in Fig. 1, include: (i) localized shear yielding, which refers to shear banding in the epoxy matrix that occurs between the rubber particles; (ii) hole or plastic void growth in the epoxy matrix, which is initiated by cavitation or debonding of the rubber particles; and (iii) rubber particle bridging behind the crack tip. Despite numerous experimental investigations on the fracture mechanisms in rubber-toughened epoxy polymers and some success in modelling the fracture behaviour of these materials under static loading conditions [9, 11], very little is known about cracktip shielding mechanisms in rubber-modified epoxies under cyclic loading conditions. Furthermore, no attempt has been made to model the FCP behaviour