Abstract
In modern manufacturing processes such as hot forming or additive manufacturing, the workpiece material undergoes very complex thermomechanical load cycles. The local mechanical properties in the component are process-dependent and the result of the different micro-structure evolution mechanisms in the material. Numerical process simulation tools aim to include more and more of these mechanisms in order to improve the accuracy of the simulations. The mechanical strength of high-performance materials such as Ti-6Al-4V depends on microstructural parameters, which are influenced by the temperature and strain histories. This contribution puts forward an implementation of a new generalized internal variables material model *MAT_GENERALIZED_PHASECHANGE in LS-DYNA. The evolution of internal variables such as phase fractions, grain size and dislocation densities can be predicted by evolution equations, and combined with yield stress models taking the contribution of the phases, grain sizes (Hall-Petch effect), and the dislocation density into account to predict the resulting mechanical properties of the processed material. The benefits of the implementation in the commercial software LS-DYNA is the possibility to solve complex coupled problems. For example, the new material law can be used to simulate hybrid manufacturing processes like forging and an additional additive manufacturing process, where changes in microstructure are highly coupled and important for the part properties.
Highlights
High-performance materials obtain their characteristic properties such as strength only by adapted production processes that control the microstructure in the material
There is a need for numerical process simulations of production processes to predict the mechanical properties resulting from the manufacturing process
While the conventional processes lead to known material properties, this is not the case for processes such as additive manufacturing followed by hot isostatic pressing (HIP) [1] and combinations of AM and metal forming [2, 3]
Summary
High-performance materials obtain their characteristic properties such as strength only by adapted production processes that control the microstructure in the material. The material properties of Ti-6Al-4V depend on the microstructure generated by phase transformations and evolution of internal variables such as dislocation densities and grain size. In most commercial tools, tailored formulations for the phase transformation kinetics are only available for a limited number of processes and materials, like the hot stamping of the manganese-boron-steel 22MnB5 [4]. Due to its “one-codestrategy” it enables the users to simulate coupled problems like the thermo-mechanical forming processes This includes phase trans-formations, which occur in materials such as steel and titanium alloys, with the LS-DYNA material model *MAT_254 / *MAT_GENERALIZED_PHASE-CHANGE. The second card controls the annealing algorithm, accounts for thermal expansion, and defines a form of internal sub-cycling to resolve non-linear effects As none of these features is used here, the respective parameters are not discussed. The abscissae of any referenced load curve represent the “target phases” and the ordinates the respective transformation parameter
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