FCG Modelling Considering the Combined Effects of Cyclic Plastic Deformation and Growth of Micro-Voids

Fatigue is one of the most prevalent mechanisms of failure. Thus, the evaluation of the fatigue crack growth process is fundamental in engineering applications subjected to cyclic loads. The fatigue crack growth rate is usually accessed through the da/dN-ΔK curves, which have some well-known limitations. In this study a numerical model that uses the cyclic plastic strain at the crack tip to predict da/dN was coupled with the Gurson–Tvergaard–Needleman (GTN) damage model. The crack propagation process occurs, by node release, when the cumulative plastic strain reaches a critical value. The GTN model is used to account for the material degradation due to the growth of micro-voids process, which affects fatigue crack growth. Predictions with GTN are compared with the ones obtained without this ductile fracture model. Crack closure was studied in order to justify the lower values of da/dN obtained in the model with GTN, when compared with the results without GTN, for lower ΔK values. Finally, the accuracy of both variants of the numerical model is accessed through the comparison with experimental results.

VistaDam: A Physics Based Ductile Fracture Model for Pressurized Pipe Failure

We present VistaDam, a physics-based ductile fracture material model that is tailored to predict failure in thin metal sheets. VistaDam is based on a three invariant plasticity model in which metal fracture is dependent on the combined evolution of the triaxial stresses as well as the third invariant of deviatoric stress. Thus, VistaDam can predict damage due to combined volumetric void growth and shear dilation; which provides VistaDam with a superior capability to describe and predict fracture in a wide range of loading ranges. VistaDam relies on three independent material parameters that can be calibrated from experimental data at different triaxiality. Calibration is achieved through the automated calibration tool VistaCal. The calibrated VistaDam material card can be readily used in explicit FEM packages such as Abaqus and LS-DYNA. In addition, the calibrated VistaDam model can be used as a virtual testing platform that can generate data required by data-driven models such as GISSMO and Johnson-Cook. This process is currently automated within VistaCal’s graphical user interface. VistaDam and VistaCal have been developed for Navy applications and have been deployed successfully to predict pressurized pipes and vessel deformation and fracture under extreme loading conditions.