Development of a semi-empirical method for obtaining the dynamic Young's modulus in random continuous reinforced glass/epoxy composites

Due to the inherent inertial effects associated with high speed testing, it may be beneficial if material properties at high strain rates could be obt ained from the use of micro-mechanics, However, it has been demonstrated th at using the rule of mixtures to predict material properties at high strain rates results in errors since the rate sensitivity of the Young's modulus and tensile strength cannot be explained solely in terms of the rate depend ence of the resin modulus and strength (respectively) measure in isolation. A number of equations for predicting the in-plane material properties of ra ndom continuous reinforced polymer composites have been suggested in the av ailable literature using empirically evaluated correction factors. The use of such factors in the determination of dynamic properties have, however, l ed to significant errors. It is therefore imperative that a method of obtai ning high speed material properties of composite laminates must be sought s ince micro-mechanics equations have not been found suitable. This was set a s the primary aim of this research work in obtaining accurate material data . In addition, the understanding of the mechanisms governing failure under high speed loadings remain largely unknown. This prompted the need to chara cterise the effect of loading rate on failure modes. Tensile tests were conducted on random continuous glass/epoxy composites at increasing rates of strain. The effect of loading rate on failure mechanis ms was investigated by viewing fractured surfaces of the tensile specimens using a scanning electron microscope (SEM). This work postulated a semi-emp irical relationship for the tensile modulus using micro-mechanics and data from tests conducted. The validity of this relationship however, needs to b e investigated further in future work.