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Article

Effect of Residual Stresses on the Fatigue Behaviour of Torsion Bars

Faculty of Mechanical Engineering, University of Maribor, Smetanova ul. 17, 2000 Maribor, Slovenia
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Metals 2020, 10(8), 1056; https://doi.org/10.3390/met10081056
Received: 1 July 2020 / Revised: 28 July 2020 / Accepted: 29 July 2020 / Published: 5 August 2020
(This article belongs to the Special Issue Fatigue Limit of Metals)
This article deals with the effect of residual stresses on the fatigue behaviour of torsion bars exposed to cyclic torsional loading with different effective loading ratios, R. The residual compressive stresses on the surface were induced during technological processes by cold surface rolling and torsional overloading (presetting) into the plastic region due to the increase in the elastic linear range for torque. In the paper, we consider two different technological processes for introducing compressive residual stress on the surface of same material. We analysed the stress states affected by different residual and applied stress using the Drucker-Prager criterion in order to determine the actual stress state. Results show that the fatigue limit can be achieved if the maximum principal stresses (combined from residual and applied stresses) do not overcome the safe stress zone. As soon as the maximum principal stress reaches the edge of the safe zone, the number of cycles to failure rapidly reduces. Experimental results show that the effective loading ratio Reff, and consequently the stress amplitude, varies through the cross section of the bar. This initiates the fatigue crack under the surface, in the highest amplitude stress zone, independent of the effective loading ratio Reff. Consequently, increasing the compressive residual stresses on the surface by a second technological process has no significant effect on fatigue crack initiation in situ far from the surface. Increasing the plastic torsional prestress can shift the maximum stress amplitude far from the surface, but a significant volume of material should remain elastically loaded in order to ensure balance with compressive stresses from the surface of the solid bar section. View Full-Text
Keywords: torsion bars; presetting; high-cycle fatigue; residual stress; multi-axial fatigue; Drucker-Prager fatigue criterion torsion bars; presetting; high-cycle fatigue; residual stress; multi-axial fatigue; Drucker-Prager fatigue criterion
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MDPI and ACS Style

Močilnik, V.; Gubeljak, N.; Predan, J. Effect of Residual Stresses on the Fatigue Behaviour of Torsion Bars. Metals 2020, 10, 1056. https://doi.org/10.3390/met10081056

AMA Style

Močilnik V, Gubeljak N, Predan J. Effect of Residual Stresses on the Fatigue Behaviour of Torsion Bars. Metals. 2020; 10(8):1056. https://doi.org/10.3390/met10081056

Chicago/Turabian Style

Močilnik, Vinko, Nenad Gubeljak, and Jožef Predan. 2020. "Effect of Residual Stresses on the Fatigue Behaviour of Torsion Bars" Metals 10, no. 8: 1056. https://doi.org/10.3390/met10081056

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