Test MethodThe use of the load separation parameter Spb method to determine the J-R curves of polypropylenes

The characterization of the fracture behaviour of polypropylenes following standard procedures is a complex task due to the difficulties encountered in the experimental measurement of the crack length. The load separation parameter Spb method is capable of determining J-R curves by testing a single pre-cracked specimen and a single blunt notched specimen. This work examines several aspects of the method, such as load separation property, its sensitivity to the initiation criterion, the influence of the blunt notched specimen used as reference and the calibration procedure. A polypropylene homopolymer and an ethylene-polypropylene block copolymer (REPSOL YPF) were analyzed. The results have shown that load separation property can be applied to both materials. Also, the initiation crack growth energy, JIC, is very sensitive to the point chosen as crack growth onset. For that reason, a criterion is proposed. Finally J-R curves are modified depending on the number of calibration points used.