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ABSTRACT--The dynamic fracture behavior of polyester/ TiO2 nanocomposites has been characterized and compared with that of the matrix material. A relationship between the dynamic stress intensity factor, K I, and the crack tip velocity, ,~, has been established. Dynamic photoelasticity coupled with high-speed photography has been used to obtain crack tip velocities and dynamic stress fields around the propagating cracks. Birefringent coatings were used to conduct the photoelastic study due to the opaqueness of the nanocomposites. Single-edge notch tension and modified compact tension specimens were used to obtain a broad range of crack velocities. Fractographic analysis was conducted to understand the fracture process. The results showed that crack arrest toughness in nanocomposites was 60% greater than in the matrix material. Crack propagation velocities prior to branching in nanocomposites were found to be 50% greater than those in polyester.

The fabrication of nanocomposites using various techniques is presented. In particular, the coupling of ultrasonics with an in-situ polymerization technique to produce nanocomposite with excellent particle dispersion, as verified by transmission electron microscopy (TEM), is discussed in detail. Dynamic fracture toughness testing is carried out on three-point bend polyester/Ti0 2 nanocomposite specimens using a modified split-Hopkinson pressure bar, and results are compared to those of the matrix material. An increase in dynamic fracture toughness relative to quasi-static fracture toughness is observed. Scanning electron microscopy (SEM) of fracture surfaces is carried out to identify toughening mechanisms. A relationship between dynamic stress intensity factor, Ki, and crack tip velocity, a, is established. Dynamic photoelasticity coupled with high speed photography has been used to obtain crack tip velocities and dynamic stress fields around the propagating cracks. Single-edge notch tension and modified compact tension specimens were used to obtain a broad range of crack velocities. Fractographic analysis was carried out to understand fracture processes. Results showed that crack arrest 339 Dynamic Fracture Mechanics Downloaded from www.worldscientific.com by UNIVERSITY OF BIRMINGHAM LIBRARY -INFORMATION SERVICES on 03/20/15. For personal use only. 340A. Shukla, V. Evora and N. Jain toughness in the nanocomposites was 60% greater than in the matrix material. Crack propagation velocities prior to incipient branching in the nanocomposites were found to be 50% greater than those in polyester.