Experimental and numerical investigation of material failure criterion with high-strength hull steel under biaxial stress

The loads, stress and strain state of the ship structures are quite complicated under the condition of collision and grounding. The failure criteria which are commonly used in numerical simulations of ship collision have limitations in evaluating the failure characteristics of hull steel under complicated stress. Based on the shell theory, complex stress in plate is simplified as plane stress. In experiments, six different shapes of specimens were designed to study the failure characteristics of high-strength hull steel under biaxial stress. The specimens were pressed with a hemispherical indenter until destruction under quasi-static loading. The displacement of specimens' midpoint and loading force were recorded. The simulation models which considering the mesh size sensitivity and the failure criteria combined with the damage evolution model have been studied. A new reasonable formula is proposed to calculate the average failure strain of different mesh size. With the application of the average failure strain, a bilinear damage evolution model for high strength hull steel in biaxial tension stress is established. Based on a plastic instable criterion, a modified BWH (m-BWH) criterion is proposed. The comparison of Constant strain (CS) criterion combined with linear damage evolution model, the BWH and m-BWH failure criteria which are combined with the bilinear damage evolution model has been performed in the simulations by Abaqus user material subroutine (VUMAT). Although the BWH criterion is more precise than the constant strain criterion in comparison with the experiment results, its errors will increase with rising of strain ratio. The m-BWH criterion improves the accuracy of the simulations when the strain ratio is high.