Abstract
In this study, a linear model of the transformation of the stress amplitude due to the mean value was used. The coefficient of the material sensitivity to cycle asymmetry with consideration of the dependence of this coefficient on the number of fatigue loading cycles is also used. A three-parameter surface model of limited stresses is proposed in this paper. The model is verified using the results of fatigue tests for cyclic bending and torsion under mean loads. The tests are performed for two types of alloy steels—S355J0 and S355J2G1W. Comparison of the allowable stress amplitudes obtained experimentally with those predicted using the proposed model shows errors of no more than 18%, with the area of the surface with the largest error being relatively small.
Highlights
Structures and elements of machines can be subjected to time-varying loads, which cause fatigue processes in the materials
Equation (14) represents a mathematical model of the limiting stress amplitude surface determined from fatigue test results for purely alternating and purely pulsating loads, assuming that the effect of the mean value on the stress amplitude is a linear function
Fatigue tests were performed under cyclic bending and cyclic torsion with the mean value of the load at fixed stress ratios R = −1, R = −0.5 and R = 0 for S355J0 steel and for fixed mean stress values σm 0, 75, 150 and 225 for S355J2G1W steel
Summary
Structures and elements of machines can be subjected to time-varying loads, which cause fatigue processes in the materials. On the basis of studies available in the literature, they performed simulation calculations, indicating that for materials sensitive to cycle asymmetry, changes in the strain–stress curve parameters result in large errors relating to fatigue damage accumulation if these changes are not taken into account. This is especially true for low-cycle loading. Based on the fatigue characteristics for the tests at R = −1 and R = 0, it is possible to determine changes in the material sensitivity coefficient to cycle asymmetry.
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