Recent Developments in LS-DYNA to close the Virtual Process Chain for Forming, Press Hardening and Welding

Transcription

1 Recent Developments in LS-DYNA to close the Virtual Process Chain for Forming, Press Hardening and Welding Thomas Klöppel 1, Andrea Erhart 1, André Haufe 1, Tobias Loose 2 1 DYNAmore GmbH, ²Ingenieurbüro Tobias Loose 18th International ESAFORM Conference on Material Forming Graz, April 2015 T. Klöppel, A. Erhart, A. Haufe, T. Loose: Recent Developments in LS-DYNA ESAFORM 2015 Graz - 1 -

2 ESAFORM 2015 Graz LS-DYNA R8 The Multiphysics Solver Combine the capabilities Explicit/ Implicit structural solver Thermal solver & heat transfer Incompressible fluid solver (ICFD) Compressible fluid solver (CESE) Electromagnetics solver (EM) Frequency domain, acoustics, modal analysis Finite elements, iso-geometric elements, ALE, EFG, SPH, DEM, CPM, User elements, materials, loads Into one scalable code for highly nonlinear transient problems static problems To enable the solution of coupled multi-physics and multi-stage problems On massively parallel systems [by courtesy of Daimler AG]

3 Plastic Work Displacement T. Klöppel, A. Erhart, A. Haufe, T. Loose: Recent Developments in LS-DYNA ESAFORM 2015 Graz LS-DYNA R8 The Multiphysics Solver No need for co-simulation, as all solvers are included! Thermal Solver Implicit Double precision EM Solver Implicit Air (BEM) Conductors (FEM) Double precision Temperature Mechanical Solver Implicit / Explicit Double precision / Single precision Fluid Solver Implicit / Explicit ICFD / CESE ALE / CPM Double precision

4 ESAFORM 2015 Graz Simulation of the manufacturing process chain For modern processes and materials, the mechanical properties of the finished part highly depend on the fabrication chain Tooling has to be compensated for springback and shape distortions which occur in the fabrication chain Numerical simulations of the complete process chain necessary to predict finished geometry and properties The individual stages pose very different requirements on the numerical solver

5 Welding in LS-DYNA T. Klöppel, A. Erhart, A. Haufe, T. Loose: Recent Developments in LS-DYNA ESAFORM 2015 Graz - 5 -

6 ESAFORM 2015 Graz [Courtesy M. Duhovic,Uni KL] Resistive Welding (Spotwelds) Inductive Welding Friction Stir Welding Fusion Welding [Courtesy Kirk Fraser, Predictive Engineering]

7 ESAFORM 2015 Graz Welding simulations additional requirements Realistic description for the heat source applied to the weld seam Weld seams are usually discretised in the pre-processing Before the weld torch has reached the material, filler should not influence the outcome When affected by the heat, material should respond as the surrounding material Due to the very high temperature, annealing effects have to be considered Material should be able to account for the microstructure of the alloy Phase changes in heating and cooling Transformation induced strains

8 Modeling Heat Sources T. Klöppel, A. Erhart, A. Haufe, T. Loose: Recent Developments in LS-DYNA ESAFORM 2015 Graz - 8 -

9 ESAFORM 2015 Graz Goldak Double Ellipsoid heat source double ellipsoidal power density distribution proposed in [Goldak2005] Most widely used for industrial applications Can be defined in LS-DYNA using keyword *BOUNDARY_THERMAL_WELD

10 ESAFORM 2015 Graz Movement of the heat source Weld torch can be assigned to moving beam Beam motion can be constraint to a trajectory linked to a nodeset (follows distortion) [Schill2014] Reference Trajectory Weld torch

11 ESAFORM 2015 Graz Movement of the heat source - example temperature

12 Heat sources with arbitrary shape LS-DYNA allows defining arbitrarily shaped heat sources Algebraic representation must be know Input as C-type or FORTRAN-type functions Ellipsoid Conoid T. Klöppel, A. Erhart, A. Haufe, T. Loose: Recent Developments in LS-DYNA ESAFORM 2015 Graz

13 ESAFORM 2015 Graz Welding simulations requirements Realistic description for the heat source applied to the weld seam Weld seams are usually discretised in the pre-processing Before the weld torch has reached the material, filler should not influence the outcome If affected by the heat, material should respond as the surrounding material Due to the very high temperature, annealing effects have to be considered Material should be able to account for the microstructure of the alloy Phase changes in heating and cooling Transformation induced strains

14 Material Modeling T. Klöppel, A. Erhart, A. Haufe, T. Loose: Recent Developments in LS-DYNA ESAFORM 2015 Graz

15 ESAFORM 2015 Graz *MAT_UHS_STEEL/*MAT_244 - Basis Material tailored for hot stamping / press hardening processes Phase transition of austenite into ferrite, pearlite, bainite and martensite for cooling Strain rate dependent thermo-elasto-plastic properties defined for individual phases Transformation induced plasticity algorithm Hardness computation Phase change kinematic as proposed by Akerström [2006, 2010]

16 ESAFORM 2015 Graz *MAT_UHS_STEEL/*MAT_244 Austenite decomposition

17 ESAFORM 2015 Graz *MAT_UHS_STEEL/*MAT_244 Extension 1 Ghost material approach for filler elements Material is inactive at the beginning, but is activated if temperature reaches the activation range from TLSTART to TLEND Properties EGHOST, PGHOST and AGHOST of ghost material should not influence the outcome, but should yield suitable mesh movement within the weld seam Similar approach for thermal material counterpart for multi-layered welding Annealing: Reset of internal variables if temperature reaches a certain limit Temperature Equivalent plastic strain

18 ESAFORM 2015 Graz *MAT_UHS_STEEL/*MAT_244 Extension 2 Phase transformation computed for heating and cooling Transformation induced plasticity due to different microstructures Transformation induced strain ferritic grid krz austinitic grid kfz

19 ESAFORM 2015 Graz Welding simulations requirements Realistic description for the heat source applied to the weld seam Weld seams are usually discretised in the pre-processing Before the weld torch has reached the material, filler should not influence the outcome If affected by the heat, material should respond as the surrounding material Due to the very high temperature, annealing effects have to be considered Material should be able to account for the microstructure of the alloy Phase changes in heating and cooling Transformation induced strains

20 Examples T. Klöppel, A. Erhart, A. Haufe, T. Loose: Recent Developments in LS-DYNA ESAFORM 2015 Graz

21 ESAFORM 2015 Graz Deep-Drawing of a Cup Welding: Two sheets (S355) with 1 mm wall thickness are laser welded Forming: The welded and distorted sheet is clamped a spherical die is pressed slowly into the sheet Model: Shell-elements for sheet, solid elements for the rest Same material model throughout the process History variables, phase proportions and deformations are accounted for in subsequent steps Welding: implicit analysis, Forming explicit analysis

22 ESAFORM 2015 Graz Welding z-displacement 10-times scaled

23 Vertical Distortion T. Klöppel, A. Erhart, A. Haufe, T. Loose: Recent Developments in LS-DYNA ESAFORM 2015 Graz

24 ESAFORM 2015 Graz Stresses in Midsurface of Shell Longitudinal stress Van Mises stress Equivalent plastic strain

25 ESAFORM 2015 Graz Microstructure ferrite bainite martensite

26 Deep drawing effectiv stress T. Klöppel, A. Erhart, A. Haufe, T. Loose: Recent Developments in LS-DYNA ESAFORM 2015 Graz

27 ESAFORM 2015 Graz Stresses in Midsurface of Shell Van Mises stress before clamping Van Mises stress after unclamping Equivalent plastic strain

28 ESAFORM 2015 Graz Deep drawing - Thinning

29 ESAFORM 2015 Graz Microstructure ferrite bainite martensite

30 Summary and Outlook T. Klöppel, A. Erhart, A. Haufe, T. Loose: Recent Developments in LS-DYNA ESAFORM 2015 Graz

31 ESAFORM 2015 Graz Summary Realistic description for the heat source applied to the weld seam Weld seams are usually discretised with solid elements in the pre-processing Before the weld torch has reached the material, filler should not influence the outcome If affected by the heat, material should respond as the surrounding material Due to the very high temperature, annealing effects have to be considered Material should be able to account for the microstructure of the alloy Phase changes in heating and cooling Transformation induced strains

32 ESAFORM 2015 Graz Outlook A generalization of *MAT_244 will be implemented Suitable for a wider range of materials More phases can be defined Multiple phase transformations Special welding contact in currently under development at LSTC Standard sliding contact at the beginning Contact switches to a tied formulation after the weld temperature is reached

33 Thank you! T. Klöppel, A. Erhart, A. Haufe, T. Loose: Recent Developments in LS-DYNA ESAFORM 2015 Graz