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Die Universität Paderborn im Februar 2023 Bildinformationen anzeigen

Die Universität Paderborn im Februar 2023

Foto: Universität Paderborn, Hannah Brauckhoff

M. Sc. Max Böhnke

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M. Sc. Max Böhnke

Werkstoff- und Fügetechnik

Wissenschaftlicher Mitarbeiter - Kennwertermittlung

Sonderforschungsbereich Transregio 285

Mitglied - Wissenschaftlicher Mitarbeiter - Teilprojekt A01

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+49 5251 60 2661
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P1.4.16.2
Besucher:
Pohlweg 47-49
33098 Paderborn

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2023

Numerical analysis of failure modeling in clinching process chain simulation

C.R. Bielak, M. Böhnke, M. Bobbert, G. Meschut, in: Materials Research Proceedings, Materials Research Forum LLC, 2023

<jats:p>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. </jats:p>


2022

Development of a Numerical 3D Model for Analyzing Clinched Joints in Versatile Process Chains

C.R. Bielak, M. Böhnke, M. Bobbert, G. Meschut, in: The Minerals, Metals &amp; Materials Series, Springer International Publishing, 2022

The application of the mechanical joining process clinching enables the joining of sheet metals with a wide range of material-thickness configurations, which is of interest in lightweight construction of multi-material structures. Each material-thickness combination results in a joint with its own property profile that is affected differently by variations. Manufacturing process-related effects from preforming steps influence the geometric shape of a clinched joint as well as its load-bearing capacity. During the clinching process high degrees of plastic strain, increased temperatures and high strain rates occur. In this context, a 3D numerical model was developed which can represent the material-specific behaviour during the process chain steps sheet metal forming, joining, and loading phase in order to achieve a high predictive accuracy of the simulation. Besides to the investigation of the prediction accuracy, the extent of the influence of individual modelling aspects such as temperature and strain rate dependency is examined.


Numerical investigation of a friction test to determine the friction coefficients for the clinching process

C.R. Bielak, M. Böhnke, M. Bobbert, G. Meschut, Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications (2022), 146442072210934

<jats:p> Clinching as a mechanical joining process has become established in many areas of car body. In order to predict relevant properties of clinched joints and to ensure the reliability of the process, it is numerically simulated during the product development process. The prediction accuracy of the simulated process depends on the implemented friction model. Therefore, a new method for determining friction coefficients in sheet metal materials was developed and tested. The aim of this study is the numerical investigation of this experimental method by means of FE simulation. The experimental setup is modelled in a 3D numerical simulation taking into account the process parameters varying in the experiment, such as geometric properties, contact pressure and contact velocity. Furthermore, the contact description of the model is calibrated via the experimentally determined friction coefficients according to clinch-relevant parameter space. It is shown that the assumptions made in the determination of the experimental data in preliminary work are valid. In addition, it is investigated to what extent the standard Coulomb friction model in the FEM can reproduce the results of the experimental method. </jats:p>


Experimental and Numerical Investigation on Manufacturing-Induced Pre-Strain on the Load-Bearing Capacity of Clinched Joints

C.R. Bielak, M. Böhnke, M. Bobbert, G. Meschut, Key Engineering Materials (2022), 926, pp. 1516-1526

Background. Clinching is a conventional cold forming process in which two or more sheets can be joined without auxiliary parts. A pre-forming of the parts to be joined, which is introduced by previous manufacturing steps, has an influence on the joining result. When considering the suitability for joining with regard to the formability of the materials, the influence of the preforming steps must be taken into account. The influences of strain hardening and sheet thickness on the joining properties must be investigated. In this context, a Finite Element Method (FEM) based metamodel analysis of the clinching process was carried out in [1] to investigate the robustness of the clinching process with respect to the different material pre-strains. In [2], the method was extended to the load bearing simulation.Procedure. The metamodel from preliminary work based on various FE models, which predicts the load-bearing capacity of a clinched joint influenced by pre-straining, is compared here with experimental data and the accuracy of the metamodel prediction is discussed. For this purpose an experimental procedure was further develop which allows the preforming of metal sheets from which joining specimens can be separated with a certain degree of unidirectional deformation. In the study, the procedure for preparing the joint specimens and the results of the loading tests are presented. Different possible relevant pre-strain combinations are investigated and compared with the simulation results, to validate the FE models and choose suitable metamodel.</jats:p>


Functionality Study of an Optical Measurement Concept for Local Force Signal Determination in High Strain Rate Tensile Tests

M. Böhnke, E. Unruh, S. Sell, M. Bobbert, D. Hein, G. Meschut, Key Engineering Materials (2022), 926, pp. 1564-1572

<jats:p>Many mechanical material properties show a dependence on the strain rate, e.g. yield stress or elongation at fracture. The quantitative description of the material behavior under dynamic loading is of major importance for the evaluation of crash safety. This is carried out using numerical methods and requires characteristic values for the materials used. For the standardized determination of dynamic characteristic values in sheet metal materials, tensile tests performed according to the guideline from [1]. A particular challenge in dynamic tensile tests is the force measurement during the test. For this purpose, strain gauges are attached on each specimen, wired to the measuring equipment and calibrated. This is a common way to determine a force signal that is as low in vibration and as free of bending moments as possible. The preparation effort for the used strain gauges are enormous. For these reasons, an optical method to determine the force by strain measurement using DIC is presented. The experiments are carried out on a high speed tensile testing system. In combioantion with a 3D DIC high speed system for optical strain measurement. The elastic deformation of the specimen in the dynamometric section is measured using strain gauges and the optical method. The measured signals are then compared to validate the presented method. The investigations are conducted using the dual phase steel material HCT590X and the aluminum material EN AW-6014 T4. Strain rates of up to 240 s-1 are investigated.</jats:p>


Development of a Modified Punch Test for Investigating the Failure Behavior in Sheet Metal Materials

M. Böhnke, C.R. Bielak, M. Bobbert, G. Meschut, in: The Minerals, Metals &amp; Materials Series, Springer International Publishing, 2022

DOI


Experimental and numerical investigation of the influence of multiaxial loading conditions on the failure behavior of clinched joints

M. Böhnke, C.R. Bielak, M. Bobbert, G. Meschut, Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications (2022)

DOI


Influence of heat treatment on the suitability for clinching of the aluminium casting alloy AlSi9

M. Neuser, M. Böhnke, O. Grydin, M. Bobbert, M. Schaper, G. Meschut, Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications (2022), 146442072210758

<jats:p> In many manufacturing areas, multi-material designs are implemented in which individual components are joined together to form complex structures with numerous joints. For example, in the automotive sector, cast components are used at the junctions of the body and joined with different types of sheet metal and extruded profiles. To be able to join structures consisting of different materials, alternative joining technologies have emerged in recent years. This includes clinching, which allows assembling of two or more thin sheet metal and casting parts by solely cold forming the material. Clinching the brittle and usually less ductile cast aluminium alloys remains a challenge because the brittle character of the cast aluminium alloys can cause cracks during the forming of the clinched joint. In this study, the influence of the heat treatment time of an aluminium casting alloy AlSi9 on the joinability in the clinching process is investigated. Specific heat treatment of the naturally hard AlSi9 leads to a modification of the eutectic microstructure, which can increase ductility. Based on this, it will be examined if specific clinching die geometries can be used, which achieve an optimized geometrical formation of the clinched joint. The load-bearing capacities of the clinched joints are determined and compared by shear tensile and head tensile tests. Furthermore, the joints are examined microscopically to investigate the influence of the heat treatment on the failure behaviour during the load-bearing tests as well as crack initiation within the joining process. </jats:p>


Clinching of Aluminum Materials – Methods for the Continuous Characterization of Process, Microstructure and Properties

R. Kupfer, D. Köhler, D. Römisch, S. Wituschek, L. Ewenz, J. Kalich, D. Weiß, B. Sadeghian, M. Busch, J.T. Krüger, M. Neuser, O. Grydin, M. Böhnke, C.R. Bielak, J. Troschitz, Journal of Advanced Joining Processes (2022), 5, 100108

Clinching as a mechanical joining technique allows a fast and reliable joining of metal sheets in large-scale production. An efficient design and dimensioning of clinched joints requires a holistic understanding of the material, the joining process and the resulting properties of the joint. In this paper, the process chain for clinching metal sheets is described and experimental techniques are proposed to analyze the process-microstructure-property relationships from the sheet metal to the joined structure. At the example of clinching aluminum EN AW 6014, characterization methods are applied and discussed for the following characteristics: the mechanical properties of the sheet materials, the tribological behavior in the joining system, the joining process and the resulting material structure, the load-bearing behavior of the joint, the damage and degradation as well as the service life and crack growth behavior. The compilation of the characterization methods gives an overview on the advantages and weaknesses of the methods and the multiple interactions of material, process and properties during clinching. In addition, the results of the analyses on EN AW 6014 can be applied for parameterization and validation of simulations.


Clinching of Aluminum Materials – Methods for the Continuous Characterization of Process, Microstructure and Properties

R. Kupfer, D. Köhler, D. Römisch, S. Wituschek, L. Ewenz, J. Kalich, D. Weiß, B. Sadeghian, M. Busch, J. Krüger, M. Neuser, O. Grydin, M. Böhnke, C.R. Bielak, J. Troschitz, Journal of Advanced Joining Processes (2022), 5, 100108

DOI


Clinching of Aluminum Materials – Methods for the Continuous Characterization of Process, Microstructure and Properties

R. Kupfer, D. Köhler, D. Römisch, S. Wituschek, L. Ewenz, J. Kalich, D. Weiß, B. Sadeghian, M. Busch, J.T. Krüger, M. Neuser, O. Grydin, M. Böhnke, C. Bielak, J. Troschitz, Journal of Advanced Joining Processes (2022), 100108

DOI


2021


Concept development of a method for identifying friction coefficients for the numerical simulation of clinching processes

M. Böhnke, M.S. Rossel, C.R. Bielak, M. Bobbert, G. Meschut, The International Journal of Advanced Manufacturing Technology (2021)

<jats:title>Abstract</jats:title><jats:p>In order to reduce fuel consumption and thus pollutant emissions, the automotive industry is increasingly developing lightweight construction concepts that are accompanied by an increasing usage of aluminum materials. Due to poor weldability of aluminum in combination with other materials, mechanical joining methods such as clinching were developed and established in series production. In order to predict the relevant characteristics of clinched joints and to ensure the reliability of the process, it is simulated numerically during product development processes. In this regard, the predictive accuracy of the simulated process highly depends on the implemented friction model. In particular, the frictional behavior between the sheet metals as well as between the sheet metal and clinching tools has a significant impact on the geometrical formation of the clinched joint. No testing methods exist that can sufficiently investigate the frictional behavior in sheet materials, especially under high interface pressures, different relative velocities, and long friction paths, while allowing a decoupled consideration of the test parameters. This paper describes the development of further testing concepts based on a proven tribo-torsion test method for determining friction coefficients between sheet metal materials for the simulation of clinching processes. For this purpose, the correlation of interface pressure and the relative velocity between aluminum and steel sheet material in clinching processes is investigated using numerical simulation. Based on these findings, the developed concepts focus on determining friction coefficients at interface pressures of the above materials, yield stress, as well as the reproduction of the occurring friction conditions between sheet metal materials and tool surfaces in clinching processes using tool substitutes. Furthermore, wear investigations between sheet metal material and tool surface were carried out in the friction tests with subsequent EDX analyses of the frictioned tool surfaces. The developed method also allows an optical deformation measurement of the sheet metal material specimen by means of digital image correlation (DIC). Based on a methodological approach, the test setups and the test systems used are explained, and the functionality of the concepts is proven by experimental tests using different sheet metal materials.</jats:p>


Influence of various procedures for the determination of flow curves on the predictive accuracy of numerical simulations for mechanical joining processes

M. Böhnke, F. Kappe, M. Bobbert, G. Meschut, Materials Testing (2021), 63(6), pp. 493-500

The predictive quality of numerical simulations for mechanical joining processes depends on the implemented material model, especially regarding the plasticity of the joining parts. Therefore, experimental material characterization processes are conducted to determine the material properties of sheet metal and generate flow curves. In this regard, there are a number of procedures which are accompanied by varying experimental efforts. This paper presents various methods of determining flow curves for HCT590X as well as EN AW-6014, including varying specimen geometries and diverse hardening laws for extrapolation procedures. The flow curves thus generated are compared considering the variety of plastic strains occurring in mechanical joining processes. The material data generated are implemented in simulation models for the joining technologies, clinching and self-piercing riveting. The influence of the varied methods on the predictive accuracy of the simulation model is analysed. The evaluation of the differing flow curves is achieved by comparing the geometric formation of the joints and the required joining forces of the processes with experimentally investigated joints.


Development of a Method for the Identification of Friction Coefficients in Sheet Metal Materials for the Numerical Simulation of Clinching Processes

M.S. Rossel, M. Böhnke, C.R. Bielak, M. Bobbert, G. Meschut, Key Engineering Materials (2021), 883, pp. 81-88

In order to reduce the fuel consumption and consequently the greenhouse emissions, the automotive industry is implementing lightweight constructions in the body in white production. As a result, the use of aluminum alloys is continuously increasing. Due to poor weldability of aluminum in combination with other materials, mechanical joining technologies like clinching are increasingly used. In order to predict relevant characteristics of clinched joints and to ensure the reliability of the process, it is simulated numerically during product development processes. In this regard the predictive accuracy of the simulated process highly depends on the implemented friction model. In particular, the frictional behavior between the sheet metals affects the geometrical formation of the clinched joint significantly. This paper presents a testing method, which enables to determine the frictional coefficients between sheet metal materials for the simulation of clinching processes. For this purpose, the correlation of interface pressure and the relative velocity between aluminum sheets in clinching processes is investigated using numerical simulation. Furthermore, the developed testing method focuses on the specimen geometry as well as the reproduction of the occurring friction conditions between two sheet metal materials in clinching processes. Based on a methodical approach the test setup is explained and the functionality of the method is proven by experimental tests using sheet metal material EN AW6014.


2020

Numerical analysis of the robustness of clinching process considering the pre-forming of the parts

C.R. Bielak, M. Böhnke, R. Beck, M. Bobbert, G. Meschut, Journal of Advanced Joining Processes. (2020)

DOI



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