The essential work of fracture of polyamide 66 filled with TiO2 nanoparticles

The fracture property of 21-nm TiO2-nanoparticle filled polyamide 66 was studied based on the essential work of fracture method. An energy-partitioned work of fracture approach was introduced, in which the resistance to crack initiation, wini, and the resistance to crack propagation, wprop, were applied. Double-edge-notched-tension specimens with different original ligament lengths were tested at a constant cross-head speed. The results showed that the essential work term of composites filled with low nanoparticle concentration notably increased, while the plastic work fairly decreased compared to that of neat matrix at room temperature. Fractography analysis suggests a three-stage evolution of crack initiation. The individual nanoparticles acted as stress concentration points, which promoted cavitations and thus induced relatively large local deformation. Thereafter, the tiny cavitations coalesced into sub-micro ones and rapidly grow into micro-voids and crack initiation due to the high-level stress concentration. The plastic work of composites was decreased with increasing nanoparticle fractions, which was due to unavoidably aggregated nanoparticles leading to high level stress concentration that favouring the crack propagation.