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A03 - Calculation and evaluation of process-induced structural material phenomena in FRP-metal compounds

The use of fibre-reinforced plastic (FRP) composites with thermoplastic matrix enables the production of lightweight structures within very short cycle times. The specific material properties, in particular formability under heat and anisotropy, enable joining connections of dissimilar joining partners with novel assembly technologies such as hot-formed bolt holes, thermoclinch connections, thermally assisted clinch joints, embedded inserts or auxiliary-free pin connections. The associated joining processes and their preparation steps are accompanied by successive local changes in the material structure of the FRP. For example, in the case of thermoformed holes in thermoplastic composites, fibres are displaced in the joining zone and thus the reinforcement structure is locally compressed, resulting in locally varying fibre volume fractions and fibre angles as well as displacements of the matrix material. This locally varying material structure effect the load-bearing behaviour of the joint results from a multitude of material and design-technological influencing parameters. The resultant material structure has been determined by means of resource-consuming structural investigations of the joining zone. Due to the limitation of the process simulation for FRP a prediction of the accurate material structure leads to a lack of information in the design process. The numerical analysis of the load-bearing capacity is carried out under the assumption of an idealised reinforcement structure and reduced single-layer characteristic values. This means that considerable potential with regard to the specific load-bearing capacity of the joint and the flexible adaptation of the joining process is currently not being exploited.

In sub-project A03 a continuous simulation chain from the joining process to the structural-mechanical evaluation of FRP/metal joints is to be developed.  The development has to consider a predictable joinability, an improved utilisation of the load transfer potential of thermoplastic composite-metal structures as well as the associated adaptability of the process chain. For this purpose, a cross-scale approach will be developed. This enables the prediction of the process-related phenomena at microscopic material structure. Furthermore, the structure can be taken into account within the framework of macroscopic load-bearing capacity analyses of hot-formed FRP joining elements at the composite level.

For this purpose, a method based on the combined Euler-Lagrangian approach for modelling and calculating the resulting material structure at micro scale of the FRP from the respective joining process are evolved. The enhanced phenomenological understanding of joining phenomena as well as the physically based approach are the basis for the material-specific flexibilisation of the process chains considered in the TR. Thus, the method enables a focused construction and design process by taken into account the varying geometry, material and process parameters and also their influence on the resulting joint.

In addition to preparate established modelling approaches at single layer level for the simulation of the mesoscopically homogenised composite behaviour for FRP/metal joints, phase I focuses in particular on the description of the process-related single fibre deformations on the basis of experimental tests at the microscale. For this process analysis, novel test environments are developed that allow a detailed investigation of the interactions of single fibres as well as fibre bundles and molten matrix. The initial and boundary conditions are applied differently. The different deformation and deflection behaviour of fibres and matrix is captured. Furthermore, direction and fibre volume content-dependent permeabilities are then derived, which can then be used to describe the hot forming process across scales.

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Characterization and Numerical Modelling of Through-Thickness Metallic-Pin-Reinforced Fibre/Thermoplastic Composites under Bending Loading

H. Böhm, H. Zhang, B. Gröger, A. Hornig, M. Gude, Journal of Composites Science (2020), 4, pp. 188

DOI


Experimental and Numerical Studies on the Deformation of a Flexible Wire in an Injection Moulding Process

D. Köhler, B. Gröger, R. Kupfer, A. Hornig, M. Gude, Procedia Manufacturing (2020), 47, pp. 940-947

DOI


Computed tomography investigation of the material structure in clinch joints in aluminium fibre-reinforced thermoplastic sheets

B. Gröger, D. Köhler, J. Vorderbrüggen, J. Troschitz, R. Kupfer, G. Meschut, M. Gude, Production Engineering (2021)

DOI


Clinching of Thermoplastic Composites and Metals—A Comparison of Three Novel Joining Technologies

B. Gröger, J. Troschitz, J. Vorderbrüggen, C. Vogel, R. Kupfer, G. Meschut, M. Gude, Materials (2021), 14, pp. 2286

Clinching continuous fibre reinforced thermoplastic composites and metals is challenging due to the low ductility of the composite material. Therefore, a number of novel clinching technologies has been developed specifically for these material combinations. A systematic overview of these advanced clinching methods is given in the present paper. With a focus on process design, three selected clinching methods suitable for different joining tasks are described in detail. The clinching processes including equipment and tools, observed process phenomena and the resultant material structure are compared. Process phenomena during joining are explained in general and compared using computed tomography and micrograph images for each process. In addition the load bearing behaviour and the corresponding failure mechanisms are investigated by means of single-lap shear tests. Finally, the new joining technologies are discussed regarding application relevant criteria.


Modelling of thermally supported clinching of fibre-reinforced thermoplastics: Approaches on mesoscale considering large deformations and fibre failure

B. Gröger, A. Hornig, A. Hoog, M. Gude, ESAFORM 2021 - 24th International Conference on Material Forming (2021)

Thermally supported clinching (Hotclinch) is a novel promising process to join dissimilar materials. Here, metal and fibre-reinforced thermoplastics (FRTP) are used within this single step joining process and without the usage of auxiliary parts like screws or rivets. For this purpose, heat is applied to improve the formability of the reinforced thermoplastic. This enables joining of the materials using conventional clinching-tools. Focus of this work is the modelling on mesoscopic scale for the numerical simulation of this process. The FTRP-model takes the material behaviour both of matrix and the fabric reinforced organo-sheet under process temperatures into account. For describing the experimentally observed phenomena such as large deformations, fibre failure and the interactions between matrix and fibres as well as between fibres themselves, the usage of conventional, purely Lagrangian based FEM methods is limited. Therefore, the combination of contact-models with advanced modelling approaches like Arbitrary-Lagrangian-Eulerian (ALE), Coupled-Eulerian-Lagrangian (CEL) and Smooth-ParticleHydrodynamics (SPH) for the numerical simulation of the clinching process are employed. The different approaches are compared with regard to simulation feasibility, robustness and results accuracy. It is shown, that the CEL approach represents the most promising approach to describe the clinching process.


Temperature dependent modelling of fibre-reinforced thermoplastic organo-sheet material for forming and joining process simulations

B. Gröger, A. Hornig, A. Hoog, M. Gude, Key Engineering Materials (2021), 883 KEM, pp. 49

Joining and local forming processes for fibre-reinforced thermoplastics (FRTP) like hole-forming or variations of the clinching process require an in-depth understanding of the process induced effects on meso-scale. For numerical modelling with a geometrical description of a woven fabric, adequate material models for a representative unit cell are identified. Model calibration is achieved employing a mesoscopic finite-element-approach using the embedded element method based on tensile tests of the consolidated organo-sheets and a phenomenological evaluation of photomicrographs. The model takes temperature dependent stiffness and fibre tension failure into account.


Forming process induced material structure of fibre-reinforced thermoplastics - Experimental and numerical investigation of a bladder-assisted moulding process

B. Gröger, V. Würfel, A. Hornig, M. Gude, Journal of Advanced Joining Processes (2022), 5

DOI


A Review on the Modeling of the Clinching Process Chain - Part II: Joining Process

B. Schramm, J. Friedlein, B. Gröger, C.R. Bielak, M. Bobbert, M. Gude, G. Meschut, T. Wallmersperger, J. Mergheim, Journal of Advanced Joining Processes (2022), 100134

DOI


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Contact

Prof. Dr.-Ing. habil. Maik Gude

Transregional Collaborative Research Centre 285

Teilprojekt A03

Maik Gude
Phone:
+49 351 463 38153

Contact

Dr. Andreas Hornig

Transregional Collaborative Research Centre 285

Teilprojekt A03

Andreas Hornig
Phone:
+49 351 463 38007

Contact

Dipl.-Ing. Benjamin Gröger

Transregional Collaborative Research Centre 285

Teilprojekt A03

Benjamin Gröger
Phone:
+49351 463 38155