Composite panels loaded by close-in charges on the water surface

Close-in blast resistance of maritime composite structures was unknown, particularly for charges on the water surface. The hull of a mine clearing vessel is typically made from fiber reinforced composite material. One of the threats for this type of vessel consist of small charges detonating close to the hull. The last decade we studied failure behavior of only typical steel ship structures for small charges positioned at close range. Therefore, we initiated an experimental series to investigate composite hull behaviour at close-in blast generated by small explosives at the water surface. Three hull designs of a composite naval ship were selected. A solid laminate, which could be used as an affordable hull solution if weight and speed of the vessel are less important. A longitudinal head stiffened hull and a sandwich hull are the two light weight alternatives. The areal mass of these latter two solutions is comparable and equal to one third of that of the solid laminate, however, the production complexity of these light weight solutions is larger. We designed a test set-up with a small pond in our bunker facility. AUTODYN simulations were performed to determine the effect of reflections given the relatively small container of water. The stand-off and charge mass in our tests were comparable as previously found critical for steel hull panels. The experiments showed that the solid composite laminate suffered minor damage. The sandwich and hat stiffened hull designs showed damage but no full breach. For all three structure types, more damage was found above the waterline than below the water line.