2600 GA Delft

This paper presents a multi-scale friction model for large-scale forming simulations. A friction framework has been de-veloped including the effect of surface changes due to normal loading and straining the underlying bulk material. A fast and efficient translation from micro to macro modeling, based on stochastic methods, is incorporated to reduce the computational effort. Adhesion and ploughing effects have been accounted for to characterize friction conditions on the micro scale. A dis-crete model has been adopted which accounts for the forma-tion of contact patches ploughing through the contacting mate-rial. To simulate metal forming processes a coupling has been made with an implicit Finite Element code. Simulations on a typ-ical metal formed product shows a distribution of friction values. The modest increase in simulation time, compared to a standard Coulomb-based FE simulation, proves the numerical feasibility of the proposed method. NOMENCLATURE α Fraction of real contact area β Asperity radius βv Linear hardening parameter γ Internal energy factor ∆G0 Activation energy ε Plastic strain ε ̇ Plastic strain rate ε0 Initial plastic strain ε̇0 Reference plastic strain rate ζ Internal energy factor η Persistence parameter θe f f Effective attack angle contact patch κ Asperity curvature λ Initial height of asperities µ Coefficient of friction ρ Asperity density σdyn Strain rate dependent stress σ f 0 Initial static stress σv0 Max. dynamic stress σwh Strain dependent stress σy Yield stress φ Normalized surface height distribution ϕ Main orientation elliptical paraboloid ψ Internal energy factor ω External energy factor ωr Remobilization parameter a Major axis elliptical paraboloi