A Finite Plasticity Gradient-Damage Model for Sheet Metals during Forming and Clinching

Abstract

In recent years, clinching has gathered popularity to join sheets of different materials in industrial applications. The manufacturing process has some advantages, as reduced joining time, reduced costs, and the joints show good fatigue properties. To ensure the joint strength, reliable simulations of the material behaviour accounting for process-induced damage are expected to be beneficial to obtain credible values for the ultimate joint strength and its fatigue limit. A finite plasticity gradient-damage material model is outlined to describe the plastic and damage evolutions during the forming of sheet metals, later applied to clinching. The utilised gradient-enhancement cures the damage-induced localisation by introducing a global damage variable as an additional finite element field. Both, plasticity and damage are strongly coupled, but can, due to a dual-surface approach, evolve independently. The ability of the material model to predict damage in strongly deformed sheets, its flexibility and its regularization properties are illustrated by numerical examples.

Numerical analysis of failure modeling in clinching process chain simulation

“…Furthermore, it was shown that the calibrated Hosford-Coulomb model can predict the failure for the process shown. In further investigations, the material model will be extended to include a non-quadratic yield criterion as well as material softening due to ductile damage using gradient enhancement for appropriate regularization, as presented in [20]. Finally, the damage model is to be implemented in process chain models in order to predict the damage and failure behavior during a pre-operation, the joining process as well as more accurately during the loading phase.…”

A calibration method for failure modeling in clinching process simulations

“…For future investigations, even more variations of punch and die geometry of the punch test will be considered to cover additional stress conditions and to calibrate the model more accurately. Moreover, the material model will be extended by a non-quadratic yield criteria as well as material softening due to ductile damage using gradient-enhancement for proper regularization like presented in [25]. Finally, the failure model will be implemented in clinching process models in order to accurately represent the damage and failure behavior during the joining process as well as during the loading phase.…”

Efficient gradient enhancements for plasticity with ductile damage in the logarithmic strain space

“…If the gradient-enhancement is placed on the local damage variable ϑ = d, as similarly done in (Horak and Jirásek, 2013;Friedlein et al, 2020;Holthusen et al, 2021), the nonlocal variable is denoted as the global damage d. Due to the affine damage combination from Eq. ( 23), the non-locality in the material model can be simply introduced by combining the truly local damage d loc with the global damage d to the local damage as…”

“…For the underlying finite plasticity formulation, Sprave and Menzel (2020); Brepols et al (2020) chose a multiplicative plasticity formulation, where the deformation gradient is multiplicatively split into elastic and plastic parts. In (Horak and Jirásek, 2013;Friedlein et al, 2020;Holthusen et al, 2022), logarithmic strain space plasticity has been used, which enables an additive split of elastic and plastic strains. Using a rotating frame formulation for plasticity, Saanouni and Hamed (2013) developed a general micromorphic theory for the gradient-enhancement of finite plasticity-damage.…”