Transient response of plates to travelling loads with application to slamming damage

Abstract

There is a considerable range of slamming loads on hull plating which cause either elastic response or elastic-plastic response where the plastic deformation is of the same order as the elastic deformation. Failure criteria for plate design can likely be from pulses causing this range of deformation. This paper summarizes the author's Master's thesis which gives a detailed analysis of the elastic response of hull plating to slamming pulses. A finite difference model of a plate strip is developed which accounts for membrane effects. The analysis shows detailed stress and deflection response to various pulses. The results of the elastic analysis give the combinations of typical pulses of 207–1380 K Pa peak pressures and decay times of 0.001–0.5 s leading to, but not exceeding, incipient yield at 276 and 414 MPa (40 000 and 60 000 psi) in various plate sizes. The plate strip concept is then extended to the elastic-plastic range. The model is made of two rigid sections with deformable hinges at the center and ends. These hinges are comprised of layers of bar elements with elastic—plastic characteristics. The results of this analysis give the permanent deflections from pulses of two—six times those which cause incipient yield. Unexpected resonances of 5–30% occur in the elastic—plastic range, not noted in the elastic range. While the slamming load is a pressure wave which propagates across a plate at some finite velocity, it is common in the analysis of hull plate slamming response to assume a spatially constant load. This paper gives justification for the approximation by analyzing the response to a travelling pressure front and specifies the criterion for which the approximation remains valid.