Achtung:

Sie haben Javascript deaktiviert!
Sie haben versucht eine Funktion zu nutzen, die nur mit Javascript möglich ist. Um sämtliche Funktionalitäten unserer Internetseite zu nutzen, aktivieren Sie bitte Javascript in Ihrem Browser.

Info-Icon This content is partly available in English
Show image information
Show image information
Show image information

C04 - Local and Integrated In-situ Analysis of Process- und Load-Caused Damage Effects in Joints

The deformation and damage phenomena that occur during the manufacture and loading of mechanical joints cannot yet be directly observed and characterised in detail due to the limited accessibility of the joint. Instead, a joint must first be unloaded and elaborately prepared and analysed, generally destructively. During this ex-situ analysis, elastic deformations reset as a result of the unloading, whereby cracks that have been introduced can potentially close. Thus these cracks cannot be detected or can only be detected to a limited extent.

The overall objective of this sub-project is the development and implementation of two complementary experimental methods for the non-destructive in-situ analysis of joints. The two methods to be developed complement each other in such a way that they enable a spatially and temporally highly resolved analysis of the joint both during its formation and under load. For the development and adaptation of the two measurement procedures as well as the phenomenological allocation of the test data, a method-based procedure for the interpretation of the temporally and spatially resolved measurement information is to be developed. The sub-project makes a significant contribution to achieving the goal of versatility in mechanical joining technology, as both the joint production and the joint load can be subjected to a detailed analysis that has not been possible so far and thus the cause-effect relationships of both life phases can be investigated.

A novel in-situ procedure using X-ray computed tomography (in-situ CT) is to be developed for local high-resolution analysis, with which the joining zone can be recorded three-dimensionally during the joining process or stress. CT as a tool for evaluating the quality of joints in larger assemblies can only be used to a limited extent due to the limited measuring volume. This is where the second method to be developed, the transient dynamic analysis (TDA), comes in. It is based on the introduction of ultrasonic waves into the joint and on the recording of the response depending on the energy contributions transmitted through the joint. The dissipated energy contributions as a result of material damage or an inadequate joint can be distinguished on the basis of their characteristics via frequency and amplitude. By introducing the ultrasonic waves, changes in the response behaviour and thus a change in the characteristic profile can be detected with high temporal resolution. Thus, the detailed CT images enable a clear assignment of the measured characteristic TDA response profiles to particular damage characteristics in the material.

Publications


Open list in Research Information System

Investigation of Clinched Joints – A Finite Element Simulation of a Non-destructive Approach

B. Sadeghian, C. Guilleaume, R. Lafarge, A. Brosius, Lecture Notes in Production Engineering (2020), pp. 116-124

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


Clinching in in-situ CT—A numerical study on suitable tool materials

D. Köhler, R. Kupfer, M. Gude, Journal of Advanced Joining Processes (2020), 2, pp. 100034

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


A New Non-destructive Testing Method Applied to Clinching

R. Lafarge, A. Wolf, C. Guilleaume, A. Brosius, Minerals, Metals and Materials Series (2021), pp. 1461

DOI


Clinching in In-situ CT – Experimental Study on Suitable Tool Materials

D. Köhler, R. Kupfer, J. Troschitz, M. Gude, ESAFORM 2021 (2021)

In lightweight design, clinching is a cost-efficient solution as the joint is created through localized cold-forming of the joining parts. A clinch point’s quality is usually assessed using ex-situ destructive testing methods. These, however, are unable to detect phenomena immediately during the joining process. For instance, elastic deformations reverse and cracks close after unloading. In-situ methods such as the force-displacement evaluation are used to control a clinching process, though deviations in the clinch point geometry cannot be derived with this method. To overcome these limitations, the clinching process can be investigated using in-situ computed tomography (in-situ CT). However, a clinching tool made of steel would cause strong artefacts and a high attenuation in the CT measurement, reducing the significance of this method. Additionally, when joining parts of the same material, the sheet-sheet interface is hardly detectable. This work aims at identifying, firstly, tool materials that allow artefact-reduced CT measurements during clinching, and, secondly, radiopaque materials that can be applied between the joining parts to enhance the detectability of the sheet-sheet interface. Therefore, both CT-suitable tool materials and radiopaque materials are selected and experimentally investigated. In the clinching process, two aluminium sheets with radiopaque material in between are clinched in a single-step (rotationally symmetric joint without cut section). It is shown that e.g. silicon nitride is suited as tool material and a tin layer is suitable to enhance the detectability of the sheet-sheet interface.


In Situ Computed Tomography—Analysis of a Single-Lap Shear Test with Clinch Points

D. Köhler, R. Kupfer, J. Troschitz, M. Gude, Materials (2021), 14, pp. 1859

As lightweight design gains more and more attention, time and cost-efficient joining methods such as clinching are becoming more popular. A clinch point’s quality is usually determined by ex situ destructive analyses such as microsectioning. However, these methods do not yield the detection of phenomena occurring during loading such as elastic deformations and cracks that close after unloading. Alternatively, in situ computed tomography (in situ CT) can be used to investigate the loading process of clinch points. In this paper, a method for in situ CT analysis of a single-lap shear test with clinched metal sheets is presented at the example of a clinched joint with two 2 mm thick aluminum sheets. Furthermore, the potential of this method to validate numerical simulations is shown. Since the sheets’ surfaces are locally in contact with each other, the interface between both aluminum sheets and therefore the exact contour of the joining partners is difficult to identify in CT analyses. To compensate for this, the application of copper varnish between the sheets is investigated. The best in situ CT results are achieved with both sheets treated. It showed that with this treatment, in situ CT is suitable to properly observe the three-dimensional deformation behavior and to identify the failure modes.


A Method for Characterization of Geometric Deviations in Clinch Points with Computed Tomography and Transient Dynamic Analysis

D. Köhler, B. Sadeghian, R. Kupfer, J. Troschitz, M. Gude, A. Brosius, Key Engineering Materials (2021), 883, pp. 89-96

When joining lightweight parts of various materials, clinching is a cost efficient solution. In a production line, the quality of a clinch point is primarily controlled by measurement of dimensions, which are accessible from outside. However, methods such as visual testing and measuring the bottom thickness as well as the outer diameter are not able to deliver any information about the most significant geometrical characteristic of the clinch point, neck thickness and undercut. Furthermore, ex-situ destructive methods such as microsectioning cannot detect elastic deformations and cracks that close after unloading. In order to exceed the current limits, a new non-destructive in-situ testing method for the clinching process is necessary. This work proposes a concept to characterize clinch points in-situ by combining two complementary non-destructive methods, namely, computed tomography (CT) and ultrasonic testing. Firstly, clinch points with different geometrical characteristics are analysed experimentally using ex-situ CT to get a highly spatially resolved 3D-image of the object. In this context, highly X-ray attenuating materials enhancing the visibility of the sheet-sheet interface are investigated. Secondly, the test specimens are modelled using finite element method (FEM) and a transient dynamic analysis (TDA) is conducted to study the effect of the geometrical differences on the deformation energy and to qualify the TDA as a fast in-situ non-destructive method for characterizing clinch points at high temporal resolution.


Characterisation of lateral offsets in clinch points with computed tomography and transient dynamic analysis

D. Köhler, B. Sadeghian, J. Troschitz, R. Kupfer, M. Gude, A. Brosius, Journal of Advanced Joining Processes (2022), 5, pp. 100089

Clinching is a very cost-efficient method for joining two or more sheets made of identical or different materials. However, the current evaluation methods cannot confirm the critical geometrical features of joints such as neck thickness, undercut, and bottom thickness. Furthermore, the effects caused by joining process such as elastic deformation and crack-closure are significant for the joining quality, but often earn insufficient attention. Therefore, computed tomography (CT) and Transient Dynamic Analysis (TDA) as an ultrasonic testing and evaluation procedure are combined to overcome the obstacles mentioned above. In order to have a well-defined and reproducible typical geometrical error in clinching, specimens with a pre-specified lateral offset of the punch with 0.1 mm, 0.2 mm are as well as with no lateral offset are investigated using CT. The specimens are treated with conductive copper varnish in varying intensities to support the two sheets' distinguishability in the CT measurement. The subsequently extracted surfaces from CT-scan data are used to create three-dimensional models for a numerical Transient Dynamic Analysis. Hereby, a harmonic force is applied to one sheet and the transferred energy is determined at the opposite side of the clinch point on the other sheet. The transmitted energy can be used as a quantitative measure for the joining quality. This setup is simulated by means of Finite-Element-Method and the specimens are investigated experimentally using a piezo actuator and a piezo sensor. The novelty of the results presented here is the completely non-destructive investigation of joint specimen by CT of similar materials with a contrast given foil in between the sheets and the subsequent TDA, which can easily detect difference between the specimens by evaluation of the energy dissipation of the joints.


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

Dr.-Ing. Robert Kupfer

Transregional Collaborative Research Centre 285

Teilprojekt C04

Robert Kupfer
Phone:
+49 351 463 38749

Contact

Dipl.-Ing. Daniel Köhler

Transregional Collaborative Research Centre 285

Teilprojekt C04

Daniel Köhler
Phone:
+49 351 463 37916

Contact

Dipl.-Ing. Richard Stephan

Transregional Collaborative Research Centre 285

Teilprojekt C04

Richard Stephan
Phone:
+49 351 463 32197