Thickness-dependent energy dissipation characteristics of laminated composites subjected to low velocity impact

This study investigates the low velocity impact properties such as damage thresholds, critical energy thresholds and damage process of laminated composites. Damage thresholds of Hertzian failure and main failure corresponding to woven and unidirectional Glass Fiber Reinforced Polymer laminates in varying thicknesses from 2 mm to 8 mm are determined through impact tests with nominal impact energies of 4, 6, and 8 J/layer. Hertzian failure and main failure thresholds of a composite laminate with a particular thickness remain substantially constant with the nominal and incipient impact energies. Energy profile and normalized energy profile diagrams are used to find out the penetration and perforation thresholds as well as explaining the correlation between the threshold energies and damage process of the laminates. Dissipated energy by a laminate is determined using a second order polynomial regression based on the relationship between energy dissipation and impact energy of data points before penetration. Penetration and perforation energies increase non-linearly with the thickness and thickness dependence is expressed using a power regression. Test results related to damage thresholds, threshold energies and effective damage area reveal that unidirectional laminates possess lower impact damage resistance and hence are more sensitive to impact damage.