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B01 - Development of methods for dimensioning parts and mechanical joints

If the safety of a joint is to be predicted, an understanding of the existing interactions is essential. Furthermore, if a prediction is to be made for an overall structure or a joined connection in a structure, it is necessary to understand the relationships between the component and the loading of a single joint is required. In a joined component, the load in a single joint depends on the properties of the joining element, the joining design, as well as the component properties and the load application. The joining design is the sum of all joining elements, their properties as well as their position. Changes to the joint or a different positioning of the joint change the loading in these points. The joining reliability must still be guaranteed for each point after such a change. The design methodology to be developed in this subproject is intended to ensure this by designing a joined component coming either from the overall structure (top-down) or from the joint (bottom-up). The methodological approach and analysis methods adapted for this purpose are intended to achieve a uniform load distribution in the joint and the component. The load in the component and joining element is determined on the basis of energy and stress variables and with the help of the developed load path analysis. Typical load types of clinching points are determined on the basis of a car body. The influence of process-related and material-related disturbance variables is considered by numerical and experimental sensitivity analysis. By changing the joining point surroundings, it is possible to influence this load distribution. The interaction between geometry and joint could be demonstrated experimentally and simulative using shear lap specimens. The redistribution can be represented and analyzed incrementally over the circumference using energy and stress variables or by using the load path analysis. In this way, cause-effect relationships between the individual influencing variables and the component and joint loadings become visible and quantifiable. This developed method can then be used to specify and evaluate simple adjustments based on the structure or the joint in a changing process chain and thus continue to ensure joint reliability.

Publications


Open list in Research Information System

A New Approach for the Evaluation of Component and Joint Loads Based on Load Path Analysis

C. Steinfelder, A. Brosius, Lecture Notes in Production Engineering (2020), pp. 134-141

DOI


Probability Distribution of Joint Point Loadings in Car Body Structures under Global Bending and Torsion

S. Martin, A.A. Camberg, T. Tröster, Procedia Manufacturing (2020), pp. 419-424


Load Path Transmission in Joining Elements

C. Steinfelder, S. Martin, A. Brosius, T. Tröster, Key Engineering Materials (2021), pp. 73-80

<jats:p>The mechanical properties of joined structures are determined considerably by the chosen joining technology. With the aim of providing a method that enables a faster and more profound decision-making in the spatial distribution of joining points during product development, a new method for the load path analysis of joining points is presented. For an exemplary car body, the load type in the joining elements, i.e. pure tensile, shear and combined tensile-shear loads, is determined using finite element analysis (FEA). Based on the evaluated loads, the resulting load paths in selected joining points are analyzed using a 2D FE-model of a clinching point. State of the art methods for load path analysis are dependent on the selected coordinate system or the existing stress state. Thus, a general statement about the load transmission path is not possible at this time. Here, a novel method for the analysis of load paths is used, which is independent of the alignment of the analyzed geometry. The basic assumption of the new load path analysis method was confirmed by using a simple specimen with a square hole in different orientations. The results presented here show a possibility to display the load transmission path invariantly. In further steps, the method will be extended for 3D analysis and the investigation of more complex assemblies. The primary goal of this methodical approach is an even load distribution over the joining elements and the component. This will provide a basis for future design approaches aimed at reducing the number of joining elements in joined structures.</jats:p>


Joining with Friction Spun Joint Connectors – Manufacturing and Analysis

C. Wischer, C. Steinfelder, W. Homberg, A. Brosius, in: IOP Conference Series: Materials Science and Engineering, 2021

DOI


Numerical and experimental investigation of the transmission moment of clinching points

C. Steinfelder, J. Kalich, A. Brosius, U. Füssel, IOP Conference Series: Materials Science and Engineering (2021), 1157, pp. 012003

In clinching, the combinations of requirements, materials, component dimensions and tools influence the resulting joint geometry and the resulting bonding mechanisms. These in turn affect the property profile of the joint. For example, it is possible to use different tools to flexibly adapt clinching points to the respective required load regime. Clinching points dimensioned in this way can be geometrically similar, but have different mechanical stress states, which leads to different properties in terms of load-bearing behavior. Within the scope of this work, the clinching process with different tools in optimal and compromise design and its effect on the force and form-closure component, is investigated in a torsion test of the clinched connection. Clinched steel sheets with two thicknesses and joining directions are analyzed. Virtual experiments are carried out using finite element analyses (FEA) of the joining process and are followed by a springback simulation. Subsequently, the surface pressure between the two joining partners in the clinching points is calculated on the basis of the results from the FEA and the transmittable moment of the connection, as an indicator for the force-closure component, is determined. Finally, the experimental and simulated data are compared and discussed.


Joining with Friction Spun Joint Connectors – Manufacturing and Analysis

C. Wischer, C. Steinfelder, W. Homberg, A. Brosius, IOP Conference Series: Materials Science and Engineering (2021), 1157, pp. 012007

Nowadays, the production of modern lightweight structures, like a body in white structure requires a wide variety of mechanical joining processes. To fulfill the various demands, mechanical joining processes and joining elements (JE) are used. Very often, they are adapted to the application, which leads in turn to a numerous of different variants, high costs, and loss of the process chain versatility. To overcome this drawback, an innovative approach is the usage of individually produced and task-adapted JE, the so-called friction spun joint connectors (FSJC). These connectors can be modified in shape as well as in material properties. This flexibility offers high potential for lightweight design but also increases the necessary analytical effort regarding the forming process as well as the manufactured joint's properties. Therefore, a new analysis strategy based on the Finite-Element-Method (FEM) is proposed, which numerically determines the local load bearing capacity within a given joint in order to identify the critical regions for load transfer. The process of joining element manufacturing and the analysis strategy will be described in detail and optimization results of the joints are shown. Numerical results are discussed and possible recommendations for joint manufacturing are derived.


A First Approach for the Treatment of Galvanic Corrosion and of Load-Bearing Capacity of Clinched Joints

S. Harzheim, C. Steinfelder, T. Wallmersperger, A. Brosius, Key Engineering Materials (2021), 883, pp. 97-104

Corrosion is a major cause for the failure of metallic components in various branches of the industry. Depending on the corrosion severity, the time until failure of the component varies. On the contrary, a study has shown that certain riveted metal joints, exposed to a short period of mechanical loading and corrosion, have greater fatigue limits. This study gives rise to the question how different corrosion exposure times affect joint metallic components. In the present research, a theoretical approach is developed in order to evaluate the influence of galvanic corrosion on joint integrity of clinched metal joints. At first, the framework for modeling galvanic corrosion is introduced. Furthermore, a simulative investigation of a clinching point is carried out based on the assumption that corrosion leads to a reduction of the contact area which leads to a local increase in contact pressure. For this purpose, the stiffness values of individual elements in a finite element model are reduced locally in the contact area of the undercut and the contact stress along a path is evaluated. Summarizing, a modeling approach is introduced to investigate corrosion effects on load-bearing behavior of clinched joints.


Identification of joints for a load-adapted shape in a body in white using steady state vehicle simulations

S. Martin, J. Schütte, C. Bäumler, W. Sextro, T. Tröster, Forces in Mechanics (2021), 6, 100065


Joint point loadings in car bodies – the influence of manufacturing tolerances and scatter in material properties

S. Martin, T. Tröster, ESAFORM 2021 (2021)


Analysis of the interactions between joint and component properties during clinching

C. Steinfelder, J. Acksteiner, C. Guilleaume, A. Brosius, Production Engineering (2022)

Clinching is a joining process that is becoming more and more important in industry due to the increasing use of multi-material designs. Despite the already widespread use of the process, there is still a need for research to understand the mechanisms and design of clinched joints. In contrast to the tool parameters, process and material disturbances have not yet been investigated to a relatively large extent. However, these also have a great influence on the properties and applicability of clinching. The effect of process disturbances on the clinched joint are investigated with numerical and experimental methods. The investigated process variations are the history of the sheets using the pre-hardening of the material, different sheet thicknesses, sheet arrangements and punch strokes. For the consideration of the material history, a specimen geometry for pre-stretching specimens in uniaxial tension is used, from which the pre-stretched secondary specimens are taken. A finite element model is set up for the numerical investigations. Suitable clinching tools are selected. With the simulation, selected process influences can be examined. The effort of the numerical investigations is considerably reduced with the help of a statistical experimental design according to Taguchi. To confirm the simulation results, experimental investigations of the clinch point geometry by using micrographs and the shear strength of the clinched joint are performed. The analysis of the influence of difference disturbance factors on the clinching process demonstrate the importance of the holistic view of the clinching process.


Numerical investigation of the clinched joint loadings considering the initial pre-strain in the joining area

S. Martin, C.R. Bielak, M. Bobbert, T. Tröster, G. Meschut, Production Engineering (2022)

<jats:title>Abstract</jats:title><jats:p>The components of a body in white consist of many individual thin-walled sheet metal parts, which usually are manufactured in deep-drawing processes. In general, the conditions in a deep-drawing process change due to changing tribology conditions, varying degrees of spring back, or scattering material properties in the sheet blanks, which affects the resulting pre-strain. Mechanical joining processes, especially clinching, are influenced by these process-related pre-strains. The final geometric shape of a clinched joint is affected to a significant level by the prior material deformation when joining with constant process parameters. That leads to a change in the stiffness and force transmission in the clinched joint due to the different geometric dimensions, such as interlock, neck thickness and bottom thickness, which directly affect the load bearing capacity. Here, the influence of the pre-straining in the deep drawing process on the force distribution in clinch points in an automotive assembly is investigated by finite-element models numerically. In further studies, the results are implemented in an optimization tool for designing clinched components. The methodology starts with a pre-straining of metal sheets. This step is followed by 2D rotationally symmetric forming simulations of the joining process. The resulting mesh of each forming simulation is rotated and 3D models are obtained. The clinched joint solid model with pre-strains is used further to determine the joint stiffnesses. With the simulation of the same test set-up with an equivalent point-connector model, the equivalent stiffness for each pre-strain combination is determined. Simulations are performed on a clinched component to assess the influence of pre-strain and sheet thinning on the clinched joint loadings by using the equivalent stiffnesses. The investigations clearly show that for the selected component, the loadings at the clinch points are dependent on the sheet thinning and the stiffnesses due to pre-strain. The magnitude of the influence varies depending on the quantity considered. For example, the shear force is more sensitive to the joint stiffness than to the sheet thinning.</jats:p>


Influence of the Surrounding Sheet Geometry on a Clinched Joint

S. Martin, K. Kurtusic, T. Tröster, Key Engineering Materials (2022), 927


Open list in Research Information System

Contact

Prof. Dr.-Ing. Alexander Brosius

Transregional Collaborative Research Centre 285

Projectnr. B01, C04

Alexander Brosius
Phone:
+49 351 463 37616

Contact

Prof. Dr. Thomas Tröster

Transregional Collaborative Research Centre 285

Teilprojekt B01

Thomas Tröster
Phone:
+49 5251 60 5331
Office:
Y2.116

Contact

Christina Guilleaume, Dipl.-Ing.

Transregional Collaborative Research Centre 285

Teilprojekte B01/C04

Christina Guilleaume
Phone:
+49 351 463 31972

Contact

Sven Martin

Transregional Collaborative Research Centre 285

Teilprojekt B01

Sven Martin
Phone:
+49 5251 605406

Contact

Dipl.-Ing. (FH) Christian Steinfelder

Transregional Collaborative Research Centre 285

Teilprojekt B01

Phone:
+49 351 463 42497