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Three-Point Bending Test and Crack Detection by Acoustic Emission on Different Spring Steel Wires with Different Crystallographic Textures



Author(s)

Mathias Lorenz¹, Mohammed. Salih¹, Daniela Schwerdt¹, Nowfal Al-Hamdany², Emad Maawad³, Norbert Schell³ and Eckehard Müller^4,5

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DOI:10.17265/2161-6213/2023.7-9.001

1. University of Wismar, Faculty of Mechanical Engineering, Ph.-Müller-Straße 14, Wismar D-23966, Germany
2. Helmholtz Zentrum Hereon, Institute of Materials Mechanics, Department of Laser Processing and Structural Assessment, Max-Planck Str. 1, Geestacht D-21502, Germany
3. Helmholtz Zentrum Hereon, Institute of Materials Physics, Max-Planck-Str.1, Geesthacht D-21502, Germany
4. Hochschule Bochum, Department of Mechatronics and Mechanical Engineering, Am Hochschulcampus 1, Bochum D-44801, Germany
5. Steinbeis-Transfercenter of Springtechnology, Part behaviour und Process, Langerfeldstr. 53 c, Iserlohn D-58638, Germany

In the production of compression springs, high forming velocities and grades of deformation during winding and setting may induce cracks that can lead to failure causing risks of an accident and damage. The AE (acoustic emission) technology, a non-destructive monitoring method, can detect acoustic signals reflected from cracks. To establish this method in the production of technical springs, it was necessary, to find out whether the AE signal is influenced by material properties, phase fractions distribution from tempered martensite, retained austenite, and microstructure including crystallographic texture. In addition, it was investigated to what extent the detected AE signal can be useful to separate between an actual crack and other material responses. Within an in-situ three-point bending test with the AE technology, macro- and micro-crack-typical AE signals were detected for five different spring steel wires (SH, VDSiCr, and FDSiCr according to EN-10270-1 and EN-10270-2). The relative energy related to the initiation, propagation, and growth of cracks caused by mechanical stress was measured using a piezoelectric sensor. If a crack AE signal appeared for the first time, the bending tests were stopped immediately. The results show that the frequency spectrum combined with the intensity of the acoustic signals generated during crack growth depends on the material properties and the crystallographic texture. Furthermore, it could be shown that it is possible to differentiate between micro-crack-typical AE signals and other signals that result from different material responses.

Technical springs, AE analysis, micro-computer tomography, texture.