Experimental study on strain-rate-dependent behavior and failure modes of long glass fiber-reinforced polypropylene composite

Due to its good mechanical performances and design flexibility, long glass fiber-reinforced polypropylene (hereinafter referred to as LGFRP) composite has been increasingly used in the automotive industry, in which the LGFRP components are likely to sustain different strain rates loading during a crash event. The objectives of this study are to investigate the correlations between the LGFRP and strain rates 10(-3)s(-1) to 50s(-1), and the corresponding failure modes of LGFRP. Therefore, tensile and compression tests are conducted at different strain rates and the corresponding microstructures of the specimens are investigated with scanning electron microscope. The experimental results show that the failure strain and ultimate strength increase as increasing strain rate. The elastic modulus is sensitive to strain rate in tensile tests, but less sensitive to strain rate in compression tests. The main failure modes of the specimens are the matrix crack and fiber pull-out. The defects such as bubbles, shrinkage cavities, or dry fibers of the specimens play important roles in the initiation and propagation of cracks during the tensile and compression tests.