Johnson-Cook Fracture Model Research Articles

Evaluation of six fracture models in high velocity perforation

A systematic evaluation of six ductile fracture models is performed to identify the most suitable fracture criterion for high velocity perforation problems. Included in the paper are the Wilkins, the Johnson–Cook, the maximum shear stress, the modified Cockcroft–Latham, the constant fracture strain, and the Bao–Wierzbicki fracture models. These six fracture models are implemented into ABAQUS/Explicit by means of a user material subroutine (VUMAT), and applied to model the failure processes of a steel and an aluminum target plate impacted by a projectile. The numerical simulations are examined by comparing with the experimental results published in the open literature. The Wilkins fracture model predicts spallation of the impacted zone of the target plate beneath the projectile. This unrealistic result is due to its power law form of the pressure term. The maximum shear stress fracture criterion fails to capture the shear plugging failure pattern in a wide range of the impact velocity. Material fracture properties cannot be fully characterized with the constant fracture strain and the modified Cockcroft–Latham fracture models. Various tensile tests on round bars do not give a consistent critical damage. The calculated residual velocities of the projectile are sensitive to the magnitude of the fracture parameters. The Johnson–Cook and the Bao–Wierzbicki fracture models formulated in the space of the stress triaxiality and the equivalent plastic strain to fracture are capable of predicting the realistic fracture patterns and at the same time the correct residual velocities. Finally, the limitations of the Johnson–Cook fracture model are discussed.

A model for erosion at normal impact

Numerical simulations of lip formation indicate that the thermal softening induced flow localisation at the edge of impact craters proposed by Sundararajan is not a general removal mechanism, which was unresolved in Hutchings' model. By considering a mechanism for erosion caused by the residual tensile stress, and applying the Johnson-Cook fracture model, the ratio of the removed volume to the indentation volume and the erosion ductility can be estimated. These are two key problems left unsolved, theoretically, in Hutching's model. The erosion model proposed in this paper can evaluate the influences of strain rate and temperature rise on the erosion rate. Comparisons of the theoretical predictions based on this model and the observed experimental erosion rates are reasonably good.