Effect of quasi-static and intermediate strain rates on the tensile properties of hybrid polymer composites

This study presents the results of an investigation on the tensile behaviour of hybrid polymer composites under different strain rates. Glass/carbon, aramid/carbon, glass/aramid, and glass/aramid/carbon hybrid laminates were produced using vacuum assisted resin transfer molding method with epoxy resin system. Uniaxial tensile testing was performed to determine the tensile strength, modulus and failure strain of the hybrid laminates under quasi static (0.001 s‒1) and intermediate (5 and 10 s‒1) strain rates. Tensile strength and elastic modulus of hybrid composites increased with increasing the strain rate. Hybrid laminates with glass fibre were more sensitive to the strain rate. Carbon layers located at the centre of the hybrid laminates resulted in increased tensile strength, indicating the major role of stacking sequence on the behaviour of hybrid composites. Scanning electron microscope (SEM) was used to examine the fracture surfaces of the laminates. The extent of damage propagation was significantly broader at intermediate strain rates.

An alternative method for the measurement of mechanical properties at intermediate strain rates: a numerical study

A feasibility study of an innovative apparatus for dynamic characterization of materials at intermediate strain rates is presented. The working principle is based on the Split Hopkinson bar, but the wave propagation occurs through properly sized springs. The system is designed to generate and transmit tension or compression waves having a low propagation speed, in order to reduce the specimen strain rate at the impact. At first, a simplified theory is presented for the estimation of longitudinal wave speed in springs as a function of the main engineering parameters of the coil dimensioning. Then, a preliminary sizing of the apparatus is proposed based on basic considerations of wave propagation theory. Finally, a numerical model of a compression test is presented as a proof-of-concept.