On the determination of fracture toughness in polymers

A method for finding the critical J-integral value, Jc, utilizing the locus line of crack initiation points, is found to be useful in determining the fracture toughness of polystyrene (PS), modified polymethylmethacrylate (PMMA), and polypropylene (PP) homopolymer. This method is also shown to be useful in determining the fracture energy at other critical points, such as the maximum load points which can occur in the nonlinear region of the load and load-point displacement curves. A theoretical equation for the calibration factor Φ for linear elastic materials is utilized in determining Jc values of polycarbonate (PC), nylon, and vinyl ester from a single test specimen. The critical J-integral values calculated using Φ or based on the locus line of crack initiation points which occurred in a fairly linear elastic range are compared with the values obtained using the critical stress intensity factor Kc.