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Procedia Engineering 10 (2011) 213–218


Influence of presetting on fatigue lifetime of torsion bars
Vinko Mo ilnika, Nenad Gubeljakb, Jožef Predanb

ERD d.o.o., Engineering, Research & Development, rne e 186, 2370 Dravograd, Slovenia University of Maribor, Faculty of Mechanical Engineering, Smetanova ul. 17, 2000 Maribor, Slovenia

Torsion bar springs are dynamically loaded machine elements which can break due to fatigue. High strength finegrain steel, grade VCN is normally used for springs or shafts. Springs are used as shock absorbers in caterpillar machines, where the diameters and lengths of the springs are limited. Springs should meet the requirements regarding spring constant (applied torque vs. twist angle), twist angle magnitude, and overcome the prescribed fatigue lifetime (number of fatigue cycles to failure). Using twist angle, it is possible to increase the elastic-plastic presetting of a torsion bar. A spring made as a torsion bar may exhibit different fatigue behaviour regarding to different elasticplastic presetting torques. Experimentally obtained results show that fatigue lifetime strongly depends on the ratio between the preset elastic-plastic torque and the applied fatigue loading range. A model for fatigue lifetime and shear stress level is proposed in spite of relative small number of tested specimens. © 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of ICM11 Keywords: Torsion bars, Presetting, Multi-axial stress state, Micro cracks, Fatigue, Twist angle, Lifetime, Torsion ;

1. Introduction
Round bar springs are common used as high strength torsion springs for vehicles and caterpillar machines. The quality of spring has an effect on fatigue lifetime in the cases of low-cyclical and highcyclical fatigue. A spring’s quality is determined by the material’s microstructure, and the thermomechanical treatment of the springs during the...
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