Project A14: Two-Scale Thermo-Mechanical Simulation of Hot Stamping

Person in Charge: Dipl.-Ing. Rudolf Neumann

Motivation:
So far, there are no models that are able to represent a continuous constitutive modelling of hot stamping considerng both an anisotropic material behaviour in austenitic state and the kinetics of phasetransformation during hardening by means of thermo-micromechanical models (TMM). Hence a method is developed to simulate the forming of an austenitic device with texture based models as well as the thermal treatment. Therefor, for the homogenization, a nonlinear model of Hashin Shtrikman type and, for the description of the phasetransformation, the Johnson-Mehl-Avrami and Koistinen-Marburger model are used. By the combination of a homogenization method with models for the phasetransformation it is possible to predict the eigenstresses due to phasetransformation. By considering the enthalpy of phasetransformation in the TMM the coupled thermo-mechanical homogenization is realized.

Investigations:

Results:

The first project phase considers the simulation of forming of an austenitic device by texture based models and by use of nonlinear models for the homogenization. In the second phase of this project, models describing the phasetransformation during quenching are integrated. Altogether, the following steps are necessary:

Formulation of a two-scaled crystal plasticity model with a homogenization method of the Hashin Shtrikman type
Formulation of the Johnson-Mehl-Avrami model and Koistinen-Marburger model
Parameteridentification for presshardenable steel
Simulation of hot forming
Continous simulation of hot stamping

So far, the nonlinear homogenization method of the Hashin-Shtrikman type is formulated and implemented into the commercial FE-solver Abaqus. Some computations and parameter studies have been accomplished for a microstructure composed of two homogenous, isotropic and ductile phases.
Furthermore, first approches to decribe the decomposition of the austenitic phase in ferrite, pearlite and martensite have been investigated. The thermo-mechanical coupling is invastigated at first for an one dimensional problem with a linear homogenization method.