Numerical implementation of a constitutive model for simulation of hot stamping

Abstract

In order to increase the accuracy of numerical simulations of the hot stamping process, an accurate and robust constitutive model is crucial. During the process, a hot blank is inserted into a tool where it is continuously formed and cooled. For the steel grades often used for this purpose, the initially austenitized blank will decompose into different product phases depending on the cooling and mechanical history. As a consequence, the phase proportions change will affect both the thermal and mechanical properties of the continuously formed and cooled blank. A thermo-elastic–plastic constitutive model based on the von Mises yield criterion with associated plastic flow is implemented into the LS-Dyna finite element code. Models accounting for the austenite decomposition and transformation induced plasticity are included in the constitutive model.The implemented model results are compared with experimental dilatation results with and without externally applied forces. Further, the calculated isothermal mechanical response during the formation of a new phase is compared with the corresponding experimental response for two different temperatures.

Characterization of ductile fracture properties of quench-hardenable boron steel: Influence of microstructure and processing conditions

“…Specifically, if the significant variations in strength and ductility arising from microstructural effects can be captured with useful accuracy, at a computational expense which can be used in crashworthiness predictions of automotive components with tailored properties. Developments concerning the constitutive modeling of boron alloyed steel that takes into account the processing history have been proposed by several investigators.Åkerström modeled the austenite decomposition into daughter phases during continuous cooling and extended it with a mechanical module to simulate the complete press hardening process [1,2]. In press hardening the boron alloyed steel 22MnB5 is a common choice in industrial application as in research and hence thoroughly investigated.…”

Development of a Tribological Test Programme Based on Press Hardening Simulations

“…Following the heating process, the numerical model commenced with a cooling process of the blank mimicking the transfer process, and this was followed by a drawing process and a cooling down process. A thermoelastic-plastic constitutive model based on the von Mises yield criterion with associated plastic flow that described the phase transformation and deformation behaviour of the blank was developed by Å kerström [5] and Å kerström et al [6]. This model was implemented in LS-Dyna, and the material properties of the boron-manganese steel at elevated temperatures could be extracted based on a previous study by Å kerström and Oldenburg [7].…”

A stress-based fracture criteria validated on mixed microstructures of ferrite and bainite over a range of stress triaxialities

“…A processing route was designed to produce tensile test specimens with a range of different volume fractions of ferrite and bainite. The production process of tailored material components has been investigated and modeled using an austenite decomposition model in combination with the linear rule of mixture to estimate the mechanical properties after quenching [1,2]. A linear rule of mixture is a simple homogenization approach; the presented model does not include fracture or damage.…”