On the Numerical Prediction of Process-Dependent Properties of Current High-Performance Materials with Material Model *MAT_254 in LS-DYNA

Abstract

Over the last years, the forecast quality in production and especially (cold) forming simulations has reached a high level at least for standard materials. It has become state-of-the-art to take the results of these process simulations into account e.g. for crashworthiness analyses. For most of the currently used high-performance materials, however, the manufacturing processes do not only result in plastic deformation and thinning of the parts. There usually is a thermal component to these processes, which significantly influences the microstructure of the material and results in a spatial distribution of material properties within the final part. In order to predict the later behavior of the part with the same quality as for standard materials and standard processes, the virtual process chain has to be closed and material models have to be used that are able to simulate the microstructure evolution during the process. The press-hardening of the manganese-boron steel grade 22MnB5 is, for example, a standard in automotive industry. For this material FEM software for process simulation tools like LS-DYNA were extended in the past to take the microstructure evolution into account. The implemented material models are tailored for this certain alloy and process. To ensure the usability of the simulation tool the material models were generalized. In LS-DYNA, material model *MAT_GENERALIZED_PHASECHANGE (*MAT_254) has been devised to serve this purpose. Core of the model is a phase evolution table that takes into account up to 24 individual phases and consequently defines up to 552 possible phase transformations, not all of which have to be defined. The appropriate transformation law for each of the phase changes can be chosen from a list of generic phase change mechanisms. Due to its relatively flexible input structure and generality of the implementation, the model has been successfully used for different processes such as press-hardening, welding, additive manufacturing, and heat treatment, and for different materials, such as ultra-high strength steels, aluminum 6xxx alloys and titanium. This contribution will introduce the material formulation in detail and show the recent extensions based on the microstructure evolution of titanium.