Issue 38

A. Bolchoun et alii, Frattura ed Integrità Strutturale, 38 (2016) 162-169; DOI: 10.3221/IGF-ESIS.18.22 162 Focussed on Multiaxial Fatigue and Fracture Fatigue life assessment of thin-walled welded joints under non-proportional load-time histories by the shear stress rate integral approach A. Bolchoun TU Darmstadt, Research Group of System Reliability and Machine Acoustics SzM, Magdalenenstr. 4, 64289 Darmstadt, Germany Fraunhofer Institute for Structural Durability and System Reliability LBF, Bartningstr. 47, 64289 Darmstadt, Germany alexandre.bolchoun@lbf.fraunhofer.de C. M. Sonsino, H. Kaufmann Fraunhofer Institute for Structural Durability and System Reliability LBF, Bartningstr. 47, 64289 Darmstadt, Germany T. Melz TU Darmstadt, Research Group of System Reliability and Machine Acoustics SzM, Magdalenenstr. 4, 64289 Darmstadt, Germany Fraunhofer Institute for Structural Durability and System Reliability LBF, Bartningstr. 47, 64289 Darmstadt, Germany A BSTRACT . Fatigue life tests under constant and variable amplitude loadings were performed on the tube-tube thin-walled welded specimens made of magnesium (AZ31 and AZ61) alloys. The tests included pure axial, pure torsional and combined in-phase and out-of-phase loadings with the load ratio   R R " ", " " 1   . For the tests with variable amplitude loads a Gauß- distributed loading spectrum with S L 4 5 10   cycles was used. Since magnesium welds show a fatigue life reduction under out-of-phase loads, a stress-based method, which takes this behavior into account, is proposed. The out-of-phase loading results in rotating shear stress vectors in the section planes, which are not orthogonal to the surface. This fact is used in order to provide an out-of-phase measure of the load. This measure is computed as an area covered by the shear stress vectors in all planes over a certain time interval, its computation involves the shear stress and the shear stress rate vectors in the individual planes. Fatigue life evaluation for the variable amplitudes loadings is performed using the Palmgren-Miner linear damage accumulation, whereas the total damage of every cycle is split up into two components: the amplitude component and the out-of-phase component. In order to compute the two components a modification of the rainflow counting method, which keeps track of the time intervals, where the cycles occur, must be used. The proposed method also takes into account different slopes of the pure axial and the pure torsional Wöhler-line by means of a Wöhler-line Citation: Bolchoun, A., Sonsino, C. M., Kaufmann, H., Melz, T., Fatigue life assessment of thin-walled welded joints under non-proportional load-time histories by the shear stress rate integral approach, Frattura ed Integrità Strutturale, 38 (2016) 162-169. Received: 12.05.2016 Accepted: 15.06.2016 Published: 01.10.2016 Copyright: © 2016 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.