The paper illustrates the application of a finite element tool for simulating the structural and damage response of foam-based sandwich composites subjected to low-velocity impact. Onset and growth of typical damage modes occurring in the composite skins, such as fibre fracture, matrix cracking and delaminations, were simulated by the use of three-dimensional damage models (for intralaminar damage) and interfacial cohesive laws (for interlaminar damage). The nonlinear behaviour of the foam core was simulated by a crushable foam plasticity model. The FE results were compared with experimental data acquired by impact testing on sandwich panels consisting of carbon/epoxy facesheets bonded to a PVC foam. Good agreement was obtained between predictions and experiments in terms of force histories, force–displacement curves and dissipated energy. The proposed model was also capable of simulating correctly nature and size of impact damage, and of capturing the key features of individual delaminations at different depth locations.

Damage prediction in composite sandwich panels subjected to low-velocity impact

Low-velocity impact response and post-impact flexural behaviour of composite sandwich structures with corrugated cores

Origami structures are commonly constructed by folding a two-dimensional sheet according to a given crease pattern. The existence of abundant crease patterns means that many three-dimensional structures can be fabricated by using a variety of sheet materials, including thin-walled tubes and arcs. Some origami structures can also be used as core structures, sandwich plates, or arcs, whereas other such structures can be stacked to form metamaterials, which are materials designed to possess a property that is not readily available in nature. Because the mechanical performances of these structures are commonly dependent upon their geometry, the properties of these structures can be designed and adjusted through the selection and optimization of the appropriate geometric parameters. This review focuses on the deformation and energy absorption (EA) capability of origami structures subjected to static and dynamic loading. The main characteristics and findings are summarized, and further work in the area is suggested.

Energy absorption of origami inspired structures and materials

Residual flexural properties of CFRP sandwich structures with aluminum honeycomb cores after low-velocity impact

Sandwich panels are used in industrial fields where lightness and energy absorption capabilities are required. In order to increase their exploitation, a wide knowledge of their mechanical behavior also in severe loading conditions is crucial. Light structures such as the one studied in the present work, sandwich panels with aluminum skins and Nomex ™ honeycomb core, are exposed to a possible decrease of their structural integrity, resulting from a low velocity impact. In order to quantitatively describe the decrease of the sandwich mechanical performance after an impact, an experimental program of compression after impact tests (CAI) has been performed. Sandwich panel specimens have been damaged during a low velocity impact test phase, using an experimental apparatus based on a free fall mass tower. Different experimental impact energies have been tested. Damaged and undamaged specimens have been consequently tested adopting a compression after impact procedure. The relation between the residual strength of the panel and the possible relevant parameters has been statistically investigated. The results show a clear reduction of the residual strength of the damaged panels compared with undamaged ones. Nevertheless, a reduced dependency between the impact energy and the residual strength is found above a certain impact energy threshold.

M. Klaus

Papers

Experimental and numerical investigations of residual strength after impact of sandwich panels