Dynamic fracture of nanocomposite materials

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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/Ti02 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 arresttoughness 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.

Publication Title

Dynamic Fracture Mechanics