High Strain-Rate Behaviors of Fiber Reinforced Composites in Principal and Off-Axis Directions

Materials can exhibit significantly different mechanical behaviors compared to quasi-static conditions at high strain rates (> 100 s-1). High strain rate tests using setups such as SHPB (Split-Hopkinson Pressure Bar) can provide, in a practicable manner, the stress-strain relations for a material at high strain rates. Such properties are vitally needed for activities such as simulation-driven impact safety design of composite structures deployed in the form of automotive body parts and assembly, and other sub-systems. Although the behaviors of isotropic and ductile materials such as various metallic alloys appear to have been extensively studied and reported in literature, dependence of mechanical properties of fiber-reinforced composites especially in different off-axis directions are extremely difficult to come across. To fill up this void, a detailed experimental study has been carried out on high strain rate mechanical characterization of orthotropic glass, carbon and a natural fiber-based polymer composite using an in-house SHPB powered by a compressed gas gun and equipped with a high speed DAQ system. A unique feature of the current study is the reporting of stress-strain curves at high strain rates when specimens are loaded in off-axis directions i.e. at angles to the principal direction (viz. 0O, 15 O, 30 O, etc.). The results highlight the substantive effect of strain rate on properties such as failure strength of a composite, and its visibly distinct behaviors in various off-axis loading directions.