@article{58492,
abstract = {{A coupled finite plasticity ductile damage and failure model is proposed for the finite element simulation of clinch joining, which incorporates stress-state dependency and regularisation by gradient-enhancement of the damage variable. Ductile damage is determined based on a failure indicator governed by a failure surface in stress space. The latter is exemplary chosen as a combination of the Hosford–Coulomb and Cockcroft–Latham–Oh failure criteria for the high and low stress triaxiality range, respectively, to cover the wide stress range encountered in forming. Damage is coupled to elasto-plasticity to capture the damage-induced degradation of the stiffness and flow stress. This affects the material behaviour up to failure, thereby realistically altering the stress state. Consequently, especially for highly ductile materials, where substantial necking and localisation precede material fracture, the failure prediction is enhanced. The resulting stress softening is regularised by gradient-enhancement to obtain mesh-objective results. The analysis of a modified punch test experiment emphasises how the damage-induced softening effect can strongly alter the actual stress state towards failure. Moreover, the impact of successful regularisation is shown, and the applicability of the damage and failure model to clinch joining is proven.}},
author = {{Friedlein, Johannes and Mergheim, Julia and Steinmann, Paul}},
issn = {{0022-5096}},
journal = {{Journal of the Mechanics and Physics of Solids}},
keywords = {{Finite plasticity, Ductile damage, Gradient-enhancement, Stress-state dependency, Failure}},
publisher = {{Elsevier BV}},
title = {{{Modelling of stress-state-dependent ductile damage with gradient-enhancement exemplified for clinch joining}}},
doi = {{10.1016/j.jmps.2025.106026}},
volume = {{196}},
year = {{2025}},
}
@article{64157,
author = {{Friedlein, Johannes and Steinmann, Paul and Mergheim, Julia}},
issn = {{0168-874X}},
journal = {{Finite Elements in Analysis and Design}},
publisher = {{Elsevier BV}},
title = {{{One-way coupled staggered implementation of gradient-enhanced damage models coupled to thermoplasticity}}},
doi = {{10.1016/j.finel.2025.104471}},
volume = {{253}},
year = {{2025}},
}
@article{59584,
author = {{Friedlein, Johannes and Lüder, Stephan and Kalich, Jan and Schmale, Hans Christian and Böhnke, Max and Schlichter, Malte Christian and Bobbert, Mathias and Meschut, Gerson and Steinmann, Paul and Mergheim, Julia}},
issn = {{2666-3309}},
journal = {{Journal of Advanced Joining Processes}},
publisher = {{Elsevier BV}},
title = {{{Application of stress-state-dependent ductile damage and failure model to clinch joining for a wide range of tool and material combinations}}},
doi = {{10.1016/j.jajp.2025.100299}},
volume = {{11}},
year = {{2025}},
}
@inproceedings{61174,
abstract = {{Abstract. Mechanical joining methods, such as clinching, are characterised by locally large plastic deformations of the sheet metal to be joined. The majority of the thereby inserted work is transformed into heat. The heat generation and temperature evolution are systematically studied herein by means of thermomechanical process simulations for joining the dual-phase steel HCT590X and the aluminium alloy EN-AW 6014. The thermal-induced softening of the material is incorporated by a suitable coupled thermoplastic constitutive model. It is observed how the tools significantly and importantly contribute to the heat exchange. They reduce peak temperature increases of 225 K (without heat transfer to tools) to less than 90 K for realistic behaviour of contact heat transfer. Overall, increases in temperature during clinch joining can be expected to remain below 90 K for steel-steel joints and around 50 K for aluminium-aluminium joints.}},
author = {{Friedlein, J. and Steinmann, P. and Mergheim, J.}},
booktitle = {{Materials Research Proceedings}},
issn = {{2474-395X}},
publisher = {{Materials Research Forum LLC}},
title = {{{Influence of thermal effects on clinch joining of sheet metal}}},
doi = {{10.21741/9781644903551-22}},
volume = {{52}},
year = {{2025}},
}
@article{58491,
abstract = {{Similar to bulk metal forming, clinch joining is characterised by large plastic deformations and a variety of different 3D stress states, including severe compression. However, inherent to plastic forming is the nucleation and growth of defects, whose detrimental effects on the material behaviour can be described by continuum damage models and eventually lead to material failure. As the damage evolution strongly depends on the stress state, a stress-state-dependent model is utilised to correctly track the accumulation. To formulate and parameterise this model, besides classical experiments, so-called modified punch tests are also integrated herein to enhance the calibration of the failure model by capturing a larger range of stress states and metal-forming-specific loading conditions. Moreover, when highly ductile materials are considered, such as the dual-phase steel HCT590X and the aluminium alloy EN AW-6014 T4 investigated here, strong necking and localisation might occur prior to fracture. This can alter the stress state and affect the actual strain at failure. This influence is captured by coupling plasticity and damage to incorporate the damage-induced softening effect. Its relative importance is shown by conducting inverse parameter identifications to determine damage and failure parameters for both mentioned ductile metals based on up to 12 different experiments.}},
author = {{Friedlein, Johannes and Böhnke, Max and Schlichter, Malte and Bobbert, Mathias and Meschut, Gerson and Mergheim, Julia and Steinmann, Paul}},
issn = {{2504-4494}},
journal = {{Journal of Manufacturing and Materials Processing}},
keywords = {{ductile damage, stress-state dependency, failure, parameter identification, punch test, clinching}},
number = {{4}},
publisher = {{MDPI AG}},
title = {{{Material Parameter Identification for a Stress-State-Dependent Ductile Damage and Failure Model Applied to Clinch Joining}}},
doi = {{10.3390/jmmp8040157}},
volume = {{8}},
year = {{2024}},
}
@inproceedings{61797,
author = {{Hollmer, Katharina and Kuczyk, Martin and Friedlein, Johannes and Mergheim, Julia and Steinmann, Paul and Zimmermann, Martina}},
title = {{{Charakterisierung des Verformungszustandes gleichartiger Stahl-Stahl-Clinchverbindungen durch Anwendung quantitativer Bildanalyse }}},
year = {{2024}},
}
@inproceedings{43462,
abstract = {{Abstract. In the numerical simulation of mechanical joining technologies such as clinching, the material modeling of the joining parts is of major importance. This includes modeling the damage and failure behavior of the materials in accordance with varying occurring stress states. This paper presents a calibration method of three different fracture models. The calibration of the models is done by use of experimental data from a modified punch test, tensile test and bulge test in order to map the occurring stress states from clinching processes and to precisely model the resulting failure behavior. Experimental investigations were carried out for an aluminum alloy EN AW-6014 in temper T4 and compared with the simulative results generated in LS-DYNA. The comparison of force-displacement curves and failure initiation shows that the Hosford–Coulomb model predicts the failure behavior for the material used and the tests applied with the best accuracy. }},
author = {{Böhnke, Max and Bielak, Christian Roman and Friedlein, Johannes and Bobbert, Mathias and Mergheim, Julia and Steinmann, Paul and Meschut, Gerson}},
booktitle = {{Materials Research Proceedings}},
issn = {{2474-395X}},
publisher = {{Materials Research Forum LLC}},
title = {{{A calibration method for failure modeling in clinching process simulations}}},
doi = {{10.21741/9781644902417-34}},
year = {{2023}},
}
@inproceedings{43463,
author = {{Friedlein, Johannes and Bielak, Christian Roman and Böhnke, Max and Bobbert, Mathias and Mergheim, Julia and Steinmann, Paul and Meschut, Gerson}},
booktitle = {{Materials Research Proceedings}},
publisher = {{Materials Research Forum LLC}},
title = {{{Influence of plastic orthotropy on clinching of sheet metal}}},
doi = {{10.21741/9781644902417-17 }},
year = {{2023}},
}
@article{56097,
abstract = {{We contrast different gradient-enhancements for plasticity-damage material models in the logarithmic strain space and compare them to reference models based on multiplicative plasticity. The models being compared include plasticity - gradient-damage, where the gradient-enhancement is applied on the local damage variable, and gradient-plasticity - damage with a gradient-enhanced plastic hardening variable. Thereby, gradient-plasticity proved to be able to simultaneously regularise plastic and ductile (plasticity-driven) damage localisation as confirmed by numerical localisation analyses. This appears to be especially advantageous for logarithmic strain space plasticity-damage, because of the observed plastic localisation even for the case of plasticity with hardening. Even though gradient-plasticity appears to be numerically more demanding, two numerical examples indicate a good robustness and mesh objectivity in the softening regime. Moreover, the internal length for plasticity is able to adjust the damage zone width, similarly to gradient-damage, however ensuring a priori that damage takes place exclusively inside the plastic zone.}},
author = {{Friedlein, Johannes and Mergheim, Julia and Steinmann, Paul}},
issn = {{0997-7538}},
journal = {{European Journal of Mechanics - A/Solids}},
keywords = {{Finite plasticity, Logarithmic strain space, Ductile damage, Gradient-enhancement, Gradient-plasticity, Gradient-damage, Loss of ellipticity}},
publisher = {{Elsevier BV}},
title = {{{Efficient gradient enhancements for plasticity with ductile damage in the logarithmic strain space}}},
doi = {{10.1016/j.euromechsol.2023.104946}},
volume = {{99}},
year = {{2023}},
}
@inproceedings{43090,
abstract = {{The application of the mechanical joining process clinching allows the assembly of different sheet metal materials with a wide range of material thickness configurations, which is of interest for lightweight multi-material structures. In order to be able to predict the clinched joint properties as a function of the individual manufacturing steps, current studies focus on numerical modeling of the entire clinching process chain. It is essential to be able to take into account the influence of the joining process-induced damage on the load-bearing capacity of the joint during the loading phase. This study presents a numerical damage accumulation in the clinching process based on an implemented Hosford-Coulomb failure model using a 3D clinching process model applied on the aluminum alloy EN AW-6014 in temper T4. A correspondence of the experimentally determined failure location with the element of the highest numerically determined damage accumulation is shown. Moreover, the experimentally determined failure behavior is predicted to be in agreement in the numerical loading simulation with transferred pre-damage from the process simulation. }},
author = {{Bielak, Christian Roman and Böhnke, Max and Friedlein, Johannes and Bobbert, Mathias and Mergheim, Julia and Steinmann, Paul and Meschut, Gerson}},
booktitle = {{Materials Research Proceedings}},
issn = {{2474-395X}},
publisher = {{Materials Research Forum LLC}},
title = {{{Numerical analysis of failure modeling in clinching process chain simulation}}},
doi = {{10.21741/9781644902417-33}},
year = {{2023}},
}
@inbook{34211,
abstract = {{Nowadays, clinching is a widely used joining technique, where sheets are joined by pure deformation to create an interlock without the need for auxiliary parts. This leads to advantages such as reduced joining time and manufacturing
costs. On the other hand, the joint strength solely relies on directed material deformation, which renders an accurate material modelling essential to reliably predict the joint forming. The formation of the joint locally involves large plastic strains and possibly complex non-proportional loading paths, as typical of many metal forming applications. Consequently, a finite plasticity formulation is utilised incorporating a Chaboche–Rousselier kinematic hardening law to capture the Bauschinger effect. Material parameters are identified from tension–compression tests on miniature spec-
imens for the dual-phase steel HCT590X. The resulting material model is implemented in LS-Dyna to study the locally diverse loading paths and give a quantitative statement on the importance of kinematic hardening for clinching. It turns out that the Bauschinger effect mainly affects the springback of the sheets and has a smaller effect on the joint forming itself.}},
author = {{Friedlein, Johannes and Mergheim, Julia and Steinmann, Paul}},
booktitle = {{The Minerals, Metals & Materials Series}},
isbn = {{9783031062117}},
issn = {{2367-1181}},
keywords = {{Clinching, Material modelling, Kinematic hardening, Parameter identification, Bauschinger effect}},
publisher = {{Springer International Publishing}},
title = {{{Influence of Kinematic Hardening on Clinch Joining of Dual-Phase Steel HCT590X Sheet Metal}}},
doi = {{10.1007/978-3-031-06212-4_31}},
year = {{2022}},
}
@article{30627,
abstract = {{Additive plasticity in the logarithmic strain space is compared to multiplicative plasticity for various loading cases including coaxial and non-coaxial plastic deformations. Even though both finite plasticity approaches are based on total Lagrangian descriptions, the former is popular due to its inherent similarity to the infinitesimal theory and its easy extensibility. However, since its introduction several limitations of additive plasticity in the logarithmic strain space have been discovered. In this study, these problems such as stress rotation and softening are considered, revealing that fundamental differences compared to multiplicative plasticity occur for non-coaxial plastic deformations. We focus in particular on the observed softer response of the additive based approach, which is analysed in depth using three numerical examples including two well-known benchmarks for finite plasticity. By means of these finite element simulations the softer and possibly even localising response of additive plasticity in the logarithmic strain space is confirmed.}},
author = {{Friedlein, J. and Mergheim, J. and Steinmann, P.}},
journal = {{International Journal of Solids and Structures}},
pages = {{111416}},
title = {{{Observations on additive plasticity in the logarithmic strain space at excessive strains}}},
doi = {{10.1016/j.ijsolstr.2021.111416}},
volume = {{239-240}},
year = {{2022}},
}
@article{34069,
author = {{Schramm, Britta and Martin, Sven and Steinfelder, Christian and Bielak, Christian Roman and Brosius, Alexander and Meschut, Gerson and Tröster, Thomas and Wallmersperger, Thomas and Mergheim, Julia}},
issn = {{2666-3309}},
journal = {{Journal of Advanced Joining Processes}},
keywords = {{Mechanical Engineering, Mechanics of Materials, Engineering (miscellaneous), Chemical Engineering (miscellaneous)}},
publisher = {{Elsevier BV}},
title = {{{A Review on the Modeling of the Clinching Process Chain - Part I: Design Phase}}},
doi = {{10.1016/j.jajp.2022.100133}},
volume = {{6}},
year = {{2022}},
}
@article{34068,
author = {{Schramm, Britta and Friedlein, Johannes and Gröger, Benjamin and Bielak, Christian Roman and Bobbert, Mathias and Gude, Maik and Meschut, Gerson and Wallmersperger, Thomas and Mergheim, Julia}},
issn = {{2666-3309}},
journal = {{Journal of Advanced Joining Processes}},
keywords = {{Mechanical Engineering, Mechanics of Materials, Engineering (miscellaneous), Chemical Engineering (miscellaneous)}},
publisher = {{Elsevier BV}},
title = {{{A Review on the Modeling of the Clinching Process Chain - Part II: Joining Process}}},
doi = {{10.1016/j.jajp.2022.100134}},
year = {{2022}},
}
@article{34070,
author = {{Schramm, Britta and Harzheim, Sven and Weiß, Deborah and Joy, Tintu David and Hofmann, Martin and Mergheim, Julia and Wallmersperger, Thomas}},
issn = {{2666-3309}},
journal = {{Journal of Advanced Joining Processes}},
keywords = {{Mechanical Engineering, Mechanics of Materials, Engineering (miscellaneous), Chemical Engineering (miscellaneous)}},
publisher = {{Elsevier BV}},
title = {{{A Review on the Modeling of the Clinching Process Chain - Part III: Operational Phase}}},
doi = {{10.1016/j.jajp.2022.100135}},
year = {{2022}},
}
@article{30647,
abstract = {{The increasing economic and ecological demands on the mobility sector require efforts to reduce resource consumption in both the production and utilization phases. The use of lightweight construction technologies can save material and increase energy efficiency during operation. Multi-material systems consisting of different materials and geometries are used to achieve weight reduction. Since conventional joining processes reach their limits in the connection of these components, new methods and technologies are necessary in order to be able to react versatilely to varying process and disturbance variables. For fundamental investigations of new possibilities in joining technology, numerical investigations are helpful to identify process parameters. To generate valid results, robust and efficient material models are developed which are adapted to the requirements of versatile joining technologies, for instance to the high plastic strains associated with self-piercing riveting. To describe the inherent strain-induced plastic orthotropy of sheet metal an anisotropic Hill-plasticity model is formulated. Tensile tests for different sheet orientations are conducted both experimentally and numerically to adjust the anisotropic material parameters by inverse parameter identification for aluminium EN AW-6014 and steel HCT590X. Then, the layer compression test is used to validate the model and the previously identified parameters.}},
author = {{Friedlein, J. and Wituschek, S. and Lechner, M. and Mergheim, J. and Steinmann, P.}},
journal = {{IOP Conference Series: Materials Science and Engineering}},
pages = {{012004}},
title = {{{Inverse parameter identification of an anisotropic plasticity model for sheet metal}}},
doi = {{10.1088/1757-899X/1157/1/012004}},
volume = {{1157}},
year = {{2021}},
}
@article{30644,
abstract = {{Computational homogenization is a powerful tool allowing to obtain homogenized properties of materials on the macroscale from simulations of the underlying microstructure. The response of the microstructure is, however, strongly affected by variations in the microstructure geometry. In particular, we consider heterogeneous materials with randomly distributed non-overlapping inclusions, which radii are also random. In this work we extend the earlier proposed non-deterministic computational homogenization framework to plastic materials, thereby increasing the model versatility and overall realism. We apply novel soft periodic boundary conditions and estimate their effect in case of non-periodic material microstructures. We study macroscopic plasticity signatures like the macroscopic von-Mises stress and make useful conclusions for further constitutive modeling. Simulations demonstrate the effect of the novel boundary conditions, which significantly differ from the standard periodic boundary conditions, and the large influence of parameter variations and hence the importance of the stochastic modeling.}},
author = {{Pivovarov, D. and Mergheim, J. and Willner, K. and Steinmann, P.}},
journal = {{Computational Mechanics}},
title = {{{Stochastic local FEM for computational homogenization of heterogeneous materials exhibiting large plastic deformations}}},
doi = {{10.1007/s00466-021-02099-x}},
year = {{2021}},
}
@article{30642,
abstract = {{Sheet metal forming as well as mechanical joining demand increasingly accurate and efficient material modelling to capture large deformations, the inherent sheet orthotropy and even process-induced damage, which is expected to be influential. To account for large strains the additive logarithmic strain space is utilised that enables a straightforward incorporation of plastic anisotropy, herein modelled by a Hill48 yield function. A gradient-enhancement is used to equip the ductile damage model with an internal length scale curing the damage-induced localisation. An affine combination of the local and non-local softening variable is derived enabling a more efficient single surface formulation for the regularised plasticity-damage material model.}},
author = {{Friedlein, J. and Mergheim, J. and Steinmann, P.}},
journal = {{PAMM}},
title = {{{Anisotropic plasticity‐damage material model for sheet metal — Regularised single surface formulation}}},
doi = {{10.1002/pamm.202100068}},
volume = {{21}},
year = {{2021}},
}
@article{30694,
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.}},
author = {{Friedlein, J. and Mergheim, J. and Steinmann, P.}},
journal = {{Key Engineering Materials}},
pages = {{57}},
title = {{{A finite plasticity gradient-damage model for sheet metals during forming and clinching}}},
doi = {{10.4028/www.scientific.net/KEM.883.57}},
volume = {{883 KEM}},
year = {{2021}},
}
@inproceedings{34208,
abstract = {{Computational homogenization is a powerful tool which allows to obtain homogenized properties of materials on the macroscale from the simulation of the underlying microstructure. The response of the microstructure is, however, strongly affected by variations in the microstructure geometry. The effect of geometry variations is even stronger in cases when the material exhibits plastic deformations. In this work we study a model of a steel alloy with arbitrary distributed elliptic voids. We model one single unit cell of the material containing one single void. The geometry of the void is not precisely known and is modeled as a variable orientation of an ellipse. Large deformations applied to the unit cell necessitate a finite elasto-plastic material model. Since the geometry variation is parameterized, we can utilize the method recently developed for stochastic problems but also applicable to all types of parametric problems — the isoparametric stochastic local FEM (SL-FEM). It is an ideal tool for problems with only a few parameters but strongly nonlinear dependency of the displacement fields on parameters. Simulations demonstrate a strong effect of parameter variation on the plastic strains and, thus, substantiate the use of the parametric computational homogenization approach.}},
author = {{Pivovarov, Dmytro and Mergheim, Julia and Willner, Kai and Steinmann, Paul}},
booktitle = {{PAMM}},
issn = {{1617-7061}},
number = {{1}},
publisher = {{Wiley}},
title = {{{Parametric FEM for computational homogenization of heterogeneous materials with random voids}}},
doi = {{10.1002/pamm.202000071}},
volume = {{20}},
year = {{2021}},
}