Experimental Characterization of Strain Rate Effect on Mechanical Properties of Thermoplastic Fiber-Reinforced Composites

Thermoplastic fiber-reinforced (TFR) composites offer several advantages over thermoset composites, such as ability to be re-molded and/or re-worked, storable at ambient temperatures, low void content, ability to be fusion welded and recyclability, which make these materials of interest for use in aerospace structures. Reliable design of such composite components requires characterization of their mechanical behavior at high strain rates as they may be subjected to dynamic loads like impact of foreign objects, projectile impacts or shock waves induced by blast loading, which produce large deformation in the material in fractions of milliseconds. Taking this into account the present work reports an experimental study on the mechanical behavior of polyphenylene sulfide (PPS) based composite laminates, reinforced with carbon and glass fibers (PPSCFC and PPSGFC), under compressive load at different strain rates. Dynamic and quasi-static tests have been carried out using a Split Hopkinson Pressure Bar (SHPB) apparatus and an electromechanical universal testing machine, respectively, over the same specimen geometry and batch. High speed imaging system was used to monitor the failure process during the test and fractography analysis was performed to aid the identification of the main failure mechanisms induced at different strain rates. Results showed that the strength and ultimate strain of the PPSGFC are strain rate dependent. An increase of 27% of the strength and 36% of the ultimate strain rate were obtained when quasi-static and dynamic results were compared while the Young Modulus remained almost constant (22.14 GPa approx.). PPSCFC’s strength average value was 531.6 MPa with a coefficient of variation of 2.7% which indicates the strength remained constant at all the strain rates. Mixed shear and delamination failure modes were observed for all specimens which indicates that damage mechanisms are not strain rate dependent for both laminates studied herein.