B2

Working Group B | Form-closed joint & Force-closed joint

 
 

Finite element analyses and simulation of the failure of short-fiber reinforced thermoplastics and aluminium blanks by clinching

Prof. Dr.-Ing. habil. Raimund Rolfes, Leibnitz Universität Hannover
Prof. Dr.-Ing. Bernd-Arno Behrens , Leibnitz Universität Hannover
Dr.-Ing. Anas Bouguecha, Leibnitz Universität Hannover

 
 

Abstract:

Due to higher requirements concerning the lightweight construction, hybrid structures are becoming increasingly important nowadays. In this context, short fiber reinforced polymers (SFRPs) offer an interesting alternative among other lightweight materials. Main reasons for using short fiber reinforced thermoplastics are shorter manufacturing times and more design flexibility, which is achieved by the applied injection molding process. Moreover, fiber reinforced thermoplastics have an excellent stiffness-density and strength-density relation compared to metals. Injection molded components are used both in the interior and in the vehicle body. Especially the construction of the vehicle body with all structural members, doors, claps, mounting parts and module systems offers great potentials for modern lightweight design and takes on greater significance for innovative concepts because of increasing functional and safety-relevant requirements.

The joining of part components made of dissimilar materials plays a key role in modern lightweight design. The conventional joining technologies such as spot welding, soldering, riveting or clinching, which are widely used to join materials of the same type, can be also used to produce hybrid joints. Among all, clinching seems to be an especially promising technology to join metals with SFRPs due to no thermal influence on the materials and low process requirements to surface finishing. One of the main challenges in designing a clinching process for such a material pair is the consideration of the quite different stiffness, plastic behavior and forming limits of these materials. These material properties, as well as the process parameters, define the resulting strength and appearance of the joint and have to be accurately modeled for a simulation-driven process design.

As a cooperation between the Institute of Structural Analysis (ISD) and the Institute of Forming Technology and Machines (IFUM), both at Leibniz Universität Hannover (LUH), in the scope of this sub-project C1 inside the SPP, the clinching process (conventional and tempered) of short fiber reinforced thermoplastics with aluminum sheets will be investigated experimentally and numerically. Thereby, the elastic-(thermo)plastic behavior, anisotropy, and material failure during the clinching process are to be regarded. This requires a thorough characterization of both, the thermoplastic material and the aluminum taking into account triaxiality, anisotropy and temperature dependency. Based on the finite element method (FEM), the (thermo)mechanical behavior of the composite and the aluminum will be modeled and integrated into an overall simulation model. By simulating the clinching process, the proof of concept of the form-fit conjunction of the hybrid material partners will be evaluated in dependence of the process parameters. Comparing the simulations with the experimental investigations with respect to the forming process and the strength of the joint, a guideline for designing, manufacturing, and testing hybrid clinching joints will be prepared finally.

 
 
Figure 1: Experimental and numerical investigations for the EN AW 5754 and PA6GF30: a) 3D computed tomography analysis, b) Constitutive modelling, c) Models verification and validation, d) 3D FE model of the clinching process, e) Numerical simulation, f) Experimental-numerical validation
Figure 1: Experimental and numerical investigations for the EN AW 5754 and PA6GF30: a) 3D computed tomography analysis, b) Constitutive modelling, c) Models verification and validation, d) 3D FE model of the clinching process, e) Numerical simulation, f) Experimental-numerical validation
 
 

The objectives of this project are:

In comparison to the first phase of the sub-project C1 in which the hybrid clinching procedure was investigated at room temperature (i.e. conventional hybrid clinching), in the second phase the tempered clinching procedure was the focus of the research work in order to minimize damage which occurs to the SFRPs sheet during the conventional clinching process. Accordingly, new findings and developments in the field of the hybrid joining of aluminium and SFRPs sheets were achieved.

In the course of material characterization, the respective material flow behavior of the pairing sheets is investigated in a fundamental manner. For this purpose, standard tensile, compressive and shear tests, as well as the hydraulic bulge test, are used. Furthermore, the 3D computer tomographic analysis is conducted to investigate the anisotropy (fiber orientation) of the composite sheet (see Fig. 1a). With regard to material modeling, the material models developed within the first phase are extended to account for the temperature dependency of the mechanical response of composites (see Fig. 1b). The extended material models are calibrated and validated against the experimental results of the material characterization (see Fig. 1c). Consequently, the material models are integrated into an overall FE model for the numerical calculation of the tempered clinching process (see Fig. 1e). Accordingly, the hybrid metal-composites clinching simulation is carried (see Fig. 1f) and validated against experimental investigations (see Fig. 1e).

The production of high-quality joints with high resistance is the ultimate goal of the manufacturing industry. Accordingly, in the third phase, the progressive damage and failure of SFRPs and aluminum will be characterized, modeled and integrated into the overall finite element model developed previously. Considering that experimental tests are very expensive and time consuming, these extensions will allow the simulation-based (virtual) assessment and improvement of the resistance of the resulting clinching joint to be carried out, which will lead a reliable and robust manufacturing hybrid clinching joints.

 
 

Publications:

2019   
  Macro-Mechanical Modeling and Experimental Validation of Anisotropic, Pressure- And Temperature-Dependent Behavior of Short Fiber Composites Dean, A.; Grbic, N.; Rolfes, R.; Behrens, B.-A.
In: Composite Structures 151 (2019) 630–643
  A FEM-Based Virtual Test-Rig For Hybrid Metal-Composites Clinching Joints Dean, A.; Grbic, N.; Rolfes, R.; Hübner, S.; Behrens, B.-A.
In: Material Science and Engineering Technology (2019)
2018   
  FE Modeling and Simulation Framework for the Forming of Hybrid Metal-Composites Clinching Joints Dean, A.; Rolfes, R.
In: Thin-Walled Structures 133 (2018), 134–140
  Parametric Study of Hybrid Metal-Composites Clinching Joints Dean, A.; Rolfes, R.; Behrens, B-A.; Hübner, S.; Chugreev, A.; Grbic, N.
In: Key Engineering Materials 767 (2018), 413-420
  Invariant-based finite strain anisotropic material model for fiber-reinforced composites. Dean, A.; Reinoso, J.; Sahraee, S.; Daum, B.; Rolfes, R.:
Sorić J., Wriggers P., Allix O. (eds) Multiscale Modeling of Heterogeneous Structures. Lecture Notes in Applied and Computational Mechanics. Springer 86 (2018)
2017   
  A thermodynamically consistent framework to couple damage and plasticity microplane-based formulations for fracture modeling: Development and algorithmic treatment. Dean, A.; Sahraee, S.; Özenc, K.; Reinoso, J.; Rolfes, R.; Kaliske, M.:
International Journal of Fracture 203 (2017) 115–134
  A new invariant-based thermo-plastic model for finite deformation analysis of short fibre reinforced composites Dean, A.; Sahraee, S.; Reinoso, J.; Rolfes, R.:
Development and numerical aspects, Composites Part B: Engineering 125 (2017) 241–258
  Finite strain anisotropic elasto-plastic model for the simulation of the forming and testing of metal/short fiber reinforced polymer clinch joints at room temperature. Dean, A.; Rolfes, R.; Behrens, B.-A.; Bouguecha, A.; Hübner, S.; Bonk, C.; Grbic, N.:
20th annual Conference on Material Forming (ESAFORM), Dublin, Ireland. AIP Conference Proceedings 1896 (2018) 030037
  A systematic approach to invariant-based anisotropic non-associative plasticity for fiber reinforced composites Daum, B.; Dean, A.; Rolfes, R.:
21th International Conference on Composites Materials (ICCM21), Xi'an, China (2017)
  Material Modeling of Short Fiber Reinforced Polymeric Composites: Theory, Numerical Aspects, and Applications Dean, A.:
Dissertation, Gottfried Wilhelm Leibniz Universität Hannover (2017)
2016   
  FEA of the Clinching Process of Short Fiber Reinforced Thermoplastic with an Aluminium Sheet using LS-DYNA. Behrens, B.-A.; Bouguecha, A.; Vucetic, M.; Grbic, N.:
19th annual Conference on Material Forming (ESAFORM), Nantes, France. AIP Conference Proceedings 1769 (2016) 100012
  An invariant-based anisotropic material model for short fiber-reinforced thermoplastics. Dean, A.; Reinoso, J.; Sahraee, S.; Rolfes, R.:
Coupled thermo-plastic formulation Composites Part A: Applied Science and Manufacturing 90 (2016) 186–199
  Finite deformation model for short fibre reinforced composites: Application to hybrid metal-composite clinching joints. Dean, A.; Sahraee, S.; Reinoso, J.; Rolfes, R.:
Composite Structures 151 (2016) 162–171
  A novel finite deformation model for short fiber reinforced composites. Dean, A.; Sahraee, S.; Reinoso, J.; Rolfes, R.:
Multiscale Modeling of Heterogeneous Structures Conference (MUMO), Dubrovnik, Croatia (2016)
2015   
  A thermodynamically consistent framework to couple microplane damage and plasticity models. Dean, A.; Reinoso, J.; Sahraee, S.; Rolfes, R.:
IV International Conference on Computational Modeling of Fracture and Failure of Materials and Structures (CFRAC15), Paris, France (2015)
  An invariant-based anisotropic thermo-plastic material model for short fiber reinforced thermoplastics. Dean, A.; Reinoso, J.; Sahraee, S.; Rolfes, R.:
20th International Conference on Composites Materials (ICCM20), Copenhagen, Denmark (2015)
2014   
  Material characterization for FEA of the clinching process of short fiber reinforced thermoplastics with an aluminum sheet. Behrens, B.-A.; Rolfes, R.; Vucetic, M.; Peshekhodov, I.; Reinoso, J.; Vogler, M.; Grbic, N.:
6th International Conference on Tribology in Manufacturing Processes & Joining by Plastic Deformation, Darmstadt, Germany.
Advanced Materials Research 966–967 (2014) 557–568
  Material modelling of short fiber reinforced thermoplastic for the FEA of a clinching test. Behrens, B.-A.; Rolfes, R.; Vucetic, M.; Reinoso, J.; Vogler, M.; Grbic, N.:
International Conference on Manufacture of Lightweight Components – ManuLight2014, Dortmund, Germany.
Procedia CIRP 18 (2014) 250–255
2013   
  Clinchen eines kurzfaserverstärkten Thermoplasten mit einem Aluminiumblechwerkstoff. Behrens, B.-A.; Hübner, S.; Götze, T.; Grbic, N.:
Umformtechnik: Gestern – Heute – Morgen,
20. Sächsische Fachtagung Umformtechnik – SFU, Dresden, Germany. Tagungsband (2013) 53–62
 

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