Numerical simulation of the Taylor impact test for laser powder bed fusion parts based on microstructural internal state variables

Abstract

The response of any engineering design components to stresses should be predictable, While the response of a material to complex loading, such as high strain rates experienced during service, is difficult to represent with simple tests, the Taylor impact test is one of a number of tests devised for high strain rate complex loading. To expedite the acceptance of LPBF Ti6Al4V (ELI) for use in demanding structural applications, there is a need to develop numerical models based on the internal microstructural state variables to predict the performance of the alloy over a wide range of high strain rates using such complex tests. This paper documents the numerical simulation of Taylor impact tests for direct metal laser-sintered and post-processed Ti6Al4V (ELI—Extra Low Interstitial) alloy. A microstructural variable-based constitutive model was used to predict the mechanical properties (stresses and evolution of plastic strains) of the material. The corresponding material parameters of the model were based on the specific microstructure obtained upon post-process heat treatment. The model was first implemented as a user material subroutine in the explicit finite element program ABAQUS using the VUHARD subroutine. Subsequently, the symmetrical Taylor impact tests of Laser Powder Bed Fusion (LPBF) Ti6Al4V (ELI) parts were numerically simulated using the VUHARD subroutine at different impact velocities. The equivalent von Mises stress and plastic strain obtained from numerical simulations were compared with the analytical solutions based on the strain rates obtained. It was shown that the instantaneous and average absolute errors between the numerical and analytical values of the model were generally less than 5%. The mushroom end, commonly observed in a Taylor test specimen, was also seen in the numerical model.