Low Velocity Impact (LVI) and Flexure-After-Impact (FAI) behaviours of rotationally moulded sandwich structures

There is limited academic knowledge and industrial understanding available on low velocity impact (LVI) properties, impact damage propagation mechanism and post impact residual strength of rotationally moulded skin-foam-skin sandwich structures. In this work, two roto-moulded sandwich structures (sandwich-1 and sandwich-2) were manufactured at the same thickness and skin layers configurations, with two different commercially available foam core material types and densities. They were tested using an instrumented drop weight impact tester at 25 J, 35 J and 45 J energy levels to analyse the force-time, force–deflections, and energy-time properties. The damage mechanism was investigated with a high-resolution X-ray micro Computed Tomography (µ-CT) technique which correlated the measured impact properties for both type of sandwich structures. Flexure-after-impact (FAI) test was carried out to characterise the effects of impact induced damage on the residual strength of impacted sandwich specimens for the first time in this study. In comparison of two sandwich structures, the lower density foam material manufactured sandwich structures (sandwich-2) showed a better impact property, damage resistance and FAI strength compared to higher density foam material sandwich structures (sandwich-1). This result was not industrially expected and could be related to the incomplete decomposition of blowing agents or forming of immature foam cells in the foaming process of higher density foam material in sandwich-1 leading to its less impact and FAI test load bearing capacities.