On the Ductile Response of Stiffened Panels Subjected to Lateral Indentation: Experimental and Numerical Analysis

Abstract

Reliable prediction of ductile fracture is essential in analysis of accidental response of ships and offshore structures. The consequences of fracture are significant. It may imply a significant reduction in structural capacity. It may also pose a potential hazard for human safety, as well as lead to an environmental and economical loss, e.g. caused by tanker collision or grounding. A series of five steel-plate indentation tests were conducted at the Norwegian University of Science and Technology (NTNU), Department of Mariner Technology, during late fall 2007. These are performed quasi-statically on various configurations of stiffened panels. The tests represent hull or deck plates in ships or platform structures subjected to accidental actions from ship-ship collisions, ship grounding or dropped object impacts. Various configurations of stiffened panels are tested, all laterally by a cone shaped indenter until fracture occurred. The specimen dimensions represent a 1:3 scale of the dimensions found in medium sized tankers, i.e. plate thickness of 5 mm. Naturally, because damaged hull and cargo tanks may cause severe environmental consequences, focus is on the plastic deformation and fracture resistance of the panels. The panel tests are primarily intended to serve as verification for advanced finite element simulations using a failure criterion based on instability mechanisms, i.e. local necking. This is implemented into the non linear explicit finite element code LS-DYNA and is referred to as the BWH instability criterion. In addition, the influence of the element size with respect to onset of failure is studied using three different element sizes for the various test cases. Although, attention is primarily placed on accidental scenarios, such as ship collision and grounding, the experimental results are of considerable relevance for other types of abnormal actions, e.g. dropped objects on deck and subsea structures, and stiffened panels subjected to explosion or ice actions.