Improvements and mechanisms of fracture and fatigue properties of well-dispersed alumina/epoxy nanocomposites

In an earlier paper [Zhao S, Schadler LS, Hillborg H, Auletta T, Duncan R. Mechanisms leading to improved mechanical performance in nanoscale alumina filled epoxy. Compos Sci Technol 2008], a model system of nanoscale alumina filled bisphenol A based epoxy with two interface conditions was used to highlight the mechanisms leading to significant improvements in ductility, tensile toughness and modulus. In this paper, the fracture toughness and fatigue crack propagation (FCP) rate of the materials used in the preceding paper were measured as a function of interface condition to gain further insight into the mechanisms leading to enhanced mechanical performance. No significant improvement in fracture toughness or fracture energy was observed. A significant improvement in FCP resistance was observed for both nanocomposites, but the improvement was larger for the composites with a stronger particle/matrix interface. The crack arresting mechanisms include particle matrix debonding, plastic void growth, and in the nanocomposites with a stronger interface, significant plastic deformation of the matrix around the well-bonded nanoparticles.