Constitutive Modelling of Anisotropy, Hardening and Failure of Sheet Metals

Engelhardt

et al. 2012

KEM

Self Cite

Sheet metal forming processes are well-established in production technology for the manufacturing of large quantities. To increase the formability, the processing limit of a single forming process can be enhanced by a combination of quasi-static and high-speed forming process. The forming limits for both operations for the aluminum alloy EN AW 6082 T6 obtained via simulations and experiment are investigated in a research cooperation between the Institute of Materials Science (IW) and the Institute of Applied Mechanics (IFAM). Significant changes in forming limits with higher strain rates are indicated by the experimental results. Here, the forming limit curves move to the lower right hand side. The processes are simulated and the FLD at fracture are predicted by means of finite element analysis. The constitutive model is based on the multiplicative split of the deformation gradient. It is coupled with ductile damage and combines nonlinear kinematic and isotropic hardening. The kinematic hardening component represents a continuum extension of the classical rheological model of Armstrong–Frederick kinematic hardening. The coupling of damage and viscoplasticity is carried out following the well-known concept of effective stress and the principle of strain equivalence. Using these powerful tools the simulation of dynamic effects and the prediction of forming limit diagrams at fracture shows good correlation with the experiments.

Section: Simulation Resultsmentioning

confidence: 99%

On the Improvement of Formability and the Prediction of Forming Limit Diagrams at Fracture by Means of Constitutive Modelling

Engelhardt

et al. 2012

KEM

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“…At the same time, the complexity of materials is increasing which leads to the necessity of detailed investigations in this field. A viscoplastic material model based on the multiplicative decomposition of the deformation gradient in the context of hyperelasticity has been used in this case [1,2]. It includes all important characteristics as the nonlinear kinematic and isotropic hardening, anisotropy and damage.…”

Section: Introductionmentioning

confidence: 99%

Simulation of Electromagnetic Forming of a Cross-Shaped Cup by Means of a Viscoplasticity Model Coupled with Damage at Finite Strains

Demir

et al. 2013

KEM

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In the field of sheet metal forming traditional forming processes are used. However, a quasi-static forming process combined with a high speed forming process can enhance the forming limits of a single one. In this paper, the investigation of the process chain quasi-static deep drawing – electromagnetic forming by means of a new coupled damage-viscoplasticity model for large deformations is performed. The finite strain constitutive model, used in the finite element simulation combines nonlinear kinematic and isotropic hardening and is derived in a thermodynamically consistent setting. The anisotropic viscoplastic model is based on the multiplicative decomposition of the deformation gradient in the context of hyperelasticity. The kinematic hardening component represents a continuum extension of the classical rheological model of Armstrong–Frederick kinematic hardening. Hill-type plastic anisotropy is modelled by expressing the yield surface as a function of second-order structure tensors as additional tensor-valued arguments. The coupling of damage and plasticity is carried out in a constitutive manner according to the effective stress concept. The constitutive equations of the material model are integrated in an explicit manner and implemented as a user material subroutine in the commercial finite element package of LS-Dyna with the electromagnetical modul. Aim of the work is to show the increasing formability of the sheet by combining quasi-static deep drawing processes with high speed electromagnetic forming process.

“…For the investigation of the process chain on a cross-shaped cup, an experimental setup has been selected which leads to a design combining a standard quasi-static deep drawing forming process with an electromagnetic pulse forming operation. A viscoplastic material model based on the multiplicative decomposition of the deformation gradient in the context of hyperelasticity has been used in this case [1,2]. It includes all important characteristics as the nonlinear kinematic and isotropic hardening, anisotropy and damage.…”

Section: Introductionmentioning

confidence: 99%

“…In this work, we have investigated the process chain on a cross-shaped cup in cooperation between the Institute of Applied Mechanics (IFAM) of the RWTH Aachen and the Institute of Forming Technology and Lightweight Construction (IUL) of the TU Dortmund. A viscoplastic material model based on the multiplicative decomposition of the deformation gradient in the context of hyperelasticity has been used [1,2]. The finite strain constitutive model combines nonlinear kinematic and isotropic hardening and is derived in a thermodynamically consistent setting.…”

mentioning

confidence: 99%

Application of a viscoplastic material model on a combined quasi‐static‐electromagnetic forming process

Demir

Proc Appl Math and Mech

et al. 2013

Self Cite

The prediction and simulation of material behavior by finite element methods has become indispensable. Furthermore, various phenomena in forming processes lead to highly differing results. In this work, we have investigated the process chain on a cross-shaped cup in cooperation between the Institute of Applied Mechanics (IFAM) of the RWTH Aachen and the Institute of Forming Technology and Lightweight Construction (IUL) of the TU Dortmund. A viscoplastic material model based on the multiplicative decomposition of the deformation gradient in the context of hyperelasticity has been used [1,2]. The finite strain constitutive model combines nonlinear kinematic and isotropic hardening and is derived in a thermodynamically consistent setting. This anisotropic viscoplastic model is based on the multiplicative decomposition of the deformation gradient in the context of hyperelasticity. The kinematic hardening component represents a continuum extension of the classical rheological model of Armstrong-Frederick kinematic hardening. The constitutive equations of the material model are integrated in an explicit manner and implemented as a user material subroutine in the commercial finite element package LS-DYNA with the electromagnetical module. The aim of the work is to show the increasing formability of the sheet by combining quasi-static deep drawing processes with high speed electromagnetic forming.