Mechanical characterization of thin injection-moulded polypropylene specimens under large in-plane shear deformations

The methodology to extract in-plane shear properties has been standardised for polymer-based composite materials. However, no standards have been designed to extract reliable test data that can be used to calibrate material models in numerical simulations for non-fibre reinforced polymers. The quality of the results from three widely used experimental techniques was examined in this study for mineral-filled polypropylene in terms of shear strain distribution, out-of-plane deformations and shear stress-strain curves with the aid of the digital image correlation method. The V-Notched Rail test (ASTM D7078) exhibited ultimate fracture of the specimen, but valid shear strain was only obtained for small deformations. For relatively large strains, more reliable shear test data were obtained from a modified version of ASTM B831: a standard test designed for aluminium but modified and implemented for polymers. Although out-of-plane deformations were avoided using aluminium holders, large variability was found in the strain distribution along the shear path. In contrast, the modified Wyoming Iosipescu test (ASTM D5379) exhibited the most robust shear stress-strain results due to consistent shear strain uniformity and low variability during the entire duration of the test.