Average true flow stress-logarithmic true strain curves can be usually obtained from a tensile test. After the onset of necking, the average true flow stress-logarithmic true strain data from a tensile specimen with round cross section should be modified by using the correction formula proposed by Bridgman. But there have been no firmly established correction formulae applicable to a specimen with rectangular cross section. In this paper, a new easy-to-use formula is presented based on parametric finite element simulations. The new formula requires only incremental plastic strain and hardening exponents of the material, which are simply presented from a tensile test. The newly proposed formula is verified with experimental data for high strength steel DH32 used in the shipbuilding and offshore industry and is proved to be effective during the diffuse necking regime.

In order to avoid the loss of human lives due to a collision of ships, it is very important to have a correct understanding on the phenomena of collision of ships and collapse of ships due to collision. A more reasonable model describing collision of ships and whole structure analysis is proposed in the present paper. Present model employs lumped masses with elasto-plastic spring system to represent striking ship considering hydrodynamic effect during collision process. When the responses of the whole structures of a striking ship and a struck one are estimated properly, more exact local structure analysis would be possible. And this makes it possible to design more reliable shock absorbing structures, soft bow for example. Quite good results are shown for behavior and deformation of striking ship by very simple calculation based upon the model proposed in the present paper.

In the present paper, the bow of the striking ship is assumed to collide the midship part of the struck ship. In the previous model, the striking ship is approximated by a lumped mass system, and the struck ship by one mass and one spring system. In the present model, the struck ship is replaced by a system composed of rigid bars and elasto-plastic hinges. This model not only can express the response of the struck ship more reasonably, but also dose not require much time for numerical simulation. Some numerical results are shown to show the effectiveness of braking panels.