Nanoindentation and nanoscratch testing of uniaxially and biaxially drawn poly(ethylene terephthalate) film

Nanoindentation and nanoscratch testing have revealed large differences in nanomechanical behaviour on uniaxially and biaxially drawn poly(ethylene terephthalate) films. Differences can be ascribed to the processing history of the film. The biaxial material exhibited significantly higher hardness and elastic modulus than the uniaxial film, presumably due to increased crystallinity from the second draw. The biaxially drawn material was also less susceptible to creep deformation. The plasticity index, the ratio of the dissipated energy to the total indentation energy, was greater on the uniaxial film, indicating that it exhibits less plastic deformation than the biaxially stretched film. The differences in processing also affected the resistance of the films to nanoscratching wear. The wear resistance of the films correlated with the ratio of the hardness to the modulus.