STRENGTH EVALUATION METHOD FOR DUCTILE FRACTURE AT STRUCTURAL DISCONTINUOUS PARTS IN THE SHIP HULL STRUCTURE UNDER COLLISION

In ship collision the absorbed energy of the hull structures by the plastic deformation is limited by the ductile fracture initiated from structural discontinuous parts, so it is very important to clarify the stress and strain state at the location where ductile crack initiates. To develop a ductile fracture evaluation method with the aid of FEM analysis, tensile breaking tests of plate specimens with structural discontinuities such as small holes or weldments were performed followed by inelastic FEM analyses considering large deformation.It was found that ductile fracture strength can be evaluated by the ductile damage parameter considering the equivalent plastic strain and the stress triaxiality, and the critical value of the damage parameter for crack initiation was estimated as 0.5 for SS 400 steel plate by the FEM analyses used in this paper.