State of the Art in Determination of Crack Direction in Shell Structures

Considerable work has been done on the modelling of fracture and necking for accidents in the maritime and offshore industry, but very little has been done to find the crack orientation during this failure. Such information will be required in future analyses which use the eXtended Finite Element Method (XFEM), rather than the element deletion approach which is typically used. It also offers a more realistic portrayal of the extents of damage, which will be useful in assessments of salvageability and residual strength analysis in maritime structures. This paper reviews the current state of the art on the direction of necking and fracture relative to the main in-plane loading axes. It was found that necking and fracture can both evolve under different angles relative to the first principal stress, depending on the ratio of inplane strains, material anisotropy, and other effects. Traditional analysis has given an easy relationship between necking orientation and strain ratio for negative second principal strains. Anisotropy is found to have a very important role for the necking angle for strain ratios (ε2/ε1) greater than 0.5. Fracture theory predicts a fracture angle perpendicular to the first principal stress for states of stress between uniaxial tension and equi-biaxial tension, but it predicts in-plane slant fracture for strain ratios less than −0.5.

On the Proportionality of Damage Rule in Finite Element Simulations of the Ductile Failure

Extended Mohr–Coulomb criterion which is uncoupled, therefore the plasticity is not influenced by the damage, was selected and calibrated. Experiments on the aluminum alloy 2024-T351 were carried out. Further, the impact of the damage rule proportionality was investigated. The damage exponent was sequentially held 1, 2 and 3, respectively. Therefore, the influence of the damage rate on the damage failure in finite element simulations was examined. Numerical simulations of the tensile test of smooth and notched cylindrical specimens and flat grooved specimen were performed. It is also shown that there is inability to predict slant fracture by uncoupled models for flat grooved specimen and in the final phase of tensile tests of cylindrical specimens.