Quasi-Static and Low-Velocity Impact Behavior of Injection Over-Molded Short/Continuous Fiber Reinforced Polypropylene Composites

Over-molded composites (combination of continuous and short fiber reinforced composites) are materials of choice for production of relatively complex load-bearing structures due to their excellent structural performance, lightweight and lower assembly cost. The quasi-static and low-velocity impact behavior of over-molded polypropylene composites with continuous fiber face sheets and short fiber core were explored by conducting flexural, drop-weight impact and compression tests. Quasi-static test results revealed that over-molded specimens showed 43% and 33% higher flexural strength and flexural modulus, respectively, compared with short fiber composites. The over-molded composites showed significant improvement of impact peak load and absorbed energy compared with short fiber composites. Optical analysis of failed over-molded impact specimens revealed impact energy-absorption though interface debonding, delamination between plies of the top and bottom inserts and damage of the core. Finally, the laminated composite inserts at top and bottom of short glass fiber reinforced polypropylene lowered the impact damage and produced higher specific compression strength than the short glass fiber reinforced polypropylene.