A simple mechanistic model to predict the macroscopic response of fibreglass-aluminium laminates under low-velocity impact

Low-velocity impact tests were carried out on fibreglass–aluminium laminates made of 2024 T3 sheets and S2-glass/epoxy prepreg layers, using an instrumented falling weight machine. In the tests, the impactor mass was held constant, whereas the energy was varied by adjusting the drop height. The load–displacement curves obtained were highly non-linear, with the specimen stiffness rapidly increasing with increasing the displacement. From the analysis of the data, the material response was unaffected by the actual speed adopted. Simple second-order polynomials, together with additional hypotheses supported by the results generated, were used to represent the load variation as a function of displacement during both the loading and the rebound phase. The resulting model, aiming to predict the contact history, consisted of three parameters, which could be determined by a minimum of experimental tests. From the model, the fundamental impact features, such as the overall force–time curve, dissipated energy, and contact duration, were effectively calculated. The damage progression with increasing the impact energy was assessed by ultrasonic C-scan and destructive analysis. Even when considerable failures were detected in the material, no clear sign of their occurrence was yielded by the fundamental impact parameters usually provided by an instrumented impact test, i.e. the force–time and force–displacement curves, the residual displacement, and the contact time. Only the extent of the damage area, plotted against the energy, underwent a sudden change in slope when a major damage took place.