Abstract
This study examined the effects of the strain rate and thermal softening on large-scale ductile fracture in ship collisions using a rate-dependent combined localized necking and fracture model. A Johnson–Cook type-hardening model, consisting of strain hardening, rate-sensitivity, and thermal softening terms, was adopted together with an associated flow rule. The temperature was treated as an internal state variable and was calculated from the plastic strain energy using a strain-rate-dependent weighting function under fully isothermal and adiabatic conditions. At every time increment, the fracture locus was updated based on the temporal strain rate, whereas the necking locus was coupled with the hardening law, which was dependent on both the strain rate and temperature. The damage indicator framework was used to consider the non-proportional loading paths. The dynamic shell-element failure model was verified through plate-panel penetration tests and applied to a large-scale ship collision analysis involving a struck ship/ship-shaped offshore installation and a supply vessel. The effects of the loading rate and impact energy were assessed in terms of the global behavior of the structure and observed failure modes.
Highlights
Assessments of the resistance of ship and offshore structural components subjected to extreme and accidental loadings, such as collision and grounding [1], explosion and blast accompanied with fire [2,3], and slamming [4], are impact engineering problems
An advanced rate-dependent plasticity and shell fracture model was used to assess the importance of strain-rate effects in large-scale ship collision analysis
Inclusion of strain rate hardening and thermal softening yields comparable results to the quasi-static simulation of ship collision problem. These effects should be omitted from a practical assessment of ship structural crashworthiness analysis against collisions
Summary
Assessments of the resistance of ship and offshore structural components subjected to extreme and accidental loadings, such as collision and grounding [1], explosion and blast accompanied with fire [2,3], and slamming [4], are impact engineering problems. Another constitutive model used widely, called the empirical Johnson–Cook model [15], considers the strain-rate and thermal softening effects separately but assuming fully adiabatic conditions for all strain rates Both the rate-dependency of the flow stress and the prediction of fracture initiation under a dynamic load require special consideration. The refined computational model developed by Cerik and Choung [21], which extended the plasticity and ductile fracture model for the shell elements advocated and validated in [17,22] for dynamic loads, was introduced as a viable means for treating strain rate effects This model was applied to a large-scale collision case study to quantify the effects of the loading speed on the structural response and deformation behavior. A comparison with predictions from the Cowper–Symonds equation, which omits this effect, was presented, and the implications of standard practices observed in the literature were discussed
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