Dynamic Response of Sandwich Plates to Medium-velocity Impact

Overall and local deflections of a single span of a continuous sandwich plate are evaluated under local contacts with a rigid indenter, at relative velocities of 10 and 20 m/s (20-40 knots), to simulate the effect of impacts that can be applied to ship sandwich structures by floating objects or moorings. Laminated carbon-vinyl ester face sheets and a H100 PVC foam core, possibly separated from the impacted face sheet by a stiff and ductile polyurethane (PUR) interlayer, comprise the sandwich plate. As in our previous study of the effect of quasi-static contacts (Suvorov, A.P. and Dvorak, G.J. (2005). Protection of Sandwich Plates from Low Velocity Impact, Journal of Composite Materials (to appear)), the focus is on the evaluation of contact forces and deflections of the face sheet and foam core interface, and on the membrane or in-plane strains in the face sheet at the contact point. These quantities are well-known potential sources of damage, causing core crushing, and face sheet delamination and/or penetration. As expected, the results show that the magnitudes of these quantities depend on both the distance of the contact point from the nearest support, and on the initial velocity of the indenter of a given mass. Both local face sheet deflections and core interface indentations are high if the impact point is within a distance from a support that is equal to 2-3 times the total sandwich plate thickness; significantly lower values are found at more distant contact points. These deflections are much reduced by replacing the foam core with an aluminum honeycomb in the supported region of the plate. However, this reinforcement elevates both the contact force and the in-plane strain in the face sheet. Therefore, thickening of the exposed face sheets should be considered around supports. Most of the kinetic energy is absorbed by the core, hence addition of the stiff and ductile PUR interlayer does not have as much effect on the results as it had in quasi-static contact.