Simulation of failure under dynamic loading at different states of triaxiality for a nickel-base superalloy

摘要

Prismatic shear and round notched tensile specimens with different geometries for variation of triaxiality were subjected to high strain rate loading in a Split-Hopkinson-Pressure-Bar device and in a high strain rate tensile machine, respectively. In finite element simulations with only a deformation model (Johnson-Cook), i.e. including thermal softening but neither a failure criterion nor damage, the load drops due to failure in the experimental force-time responses cannot be reproduced. Therefore a constitutive model for ductile damage based on plastic work has been developed taking into account the nonlinear influence of triaxiality on the failure behaviour. Partial linearisation of the ductile damage model with respect to the strain-rate and temperature dependence leads to the Johnson-Cook failure model for the critical cumulated strain. It is shown for both, ductile damage and failure model, that they are capable to meet the experimentally obtained results under a wide range of triaxialities with only one set of constitutive parameters per model. The Split-Hopkinson-Pressure-Bar set-up was also used for experimental chip formation at high speed orthogonal cutting. Simulations with the ductile damage model show an adequate chip segmentation.