Micro-mechanical modelling of ductile damage and tearing - results of a European numerical round robin

Results of a European numerical round robin on the application of constitutive equations for ductile damage to simulate tearing of a ferritic steel are presented. The analysis of deformation and failure of a standard smooth tensile specimen is used to characterize the material and identify, critical damage parameters for ductile tearing. Ductile crack growth in a C(T) specimen is then numerically simulated by applying the constitutive models of Gurson or Rousselier in order to predict a F-R-curve. Although the tensile tests were satisfactorily described, two main problems arose. The first one is that the participants' results differ considerably from each other with respect to the critical damage parameter obtained in the first task and the predicted F-R-curves in the second. The reasons were partially found in the strategies for parameter identification and the non-unique definitions for crack initiation and crack growth used in the simulations. Further reasons are expected in the individual realization of the damage model in the FE programmes or user subroutines. The second problem is a general discrepancy between the simulations and the experiment: most of the predicted F-R-curves are too flat compared with the experimental one. Manifold conclusions can be drawn for future work aiming at improving the reliability of the numerical models and promoting their application in engineering practice.