Mechanical behavior of bio-inspired helicoidal thermoplastic composites

Helicoidal composite has been found naturally existing in many species of crustaceans and it has recently raised a significant amount of interests among researchers due to its great impact performance resulted from unique fiber layup architecture. This work is focused on developing a novel bio-inspired helicoidal thermoplastic composite and studying its mechanical behaviors under different testing conditions. Continuous glass fiber reinforced polypropylene composite preforms were used for compression molding the helicoidal structure with a pitch angle of 16.3° and nonlinear pitch angle. Composites with conventional fiber layups such as 0/90 and quasi-isotropic layup sequences were also prepared and tested for comparison purpose. Various tests at different strain rates, including quasi-static test (flexural test and compression after impact test), low strain rate test (Izod impact test and drop tower impact test), and high strain rate test (Split Hopkinson pressure bar test), were performed to evaluate the mechanical properties of the helicoidal composites and conventional composites. The helicoidal composites showed twisting fracture pattern for deflecting cracks involving more areas for energy absorption in addition to common failure mechanisms in the Izod impact test. It was also found that the helicoidal composite showed considerably higher damage tolerance than the conventional composites in high strain rate scenarios.