Stress based fatigue life assessment of sintered steels and aluminium under variable amplitude loading

Abstract

This paper aims to give an insight into the reliability of fatigue life assessment results for powder metallurgy (PM) components subjected to variable amplitude loading. In this study, notched specimens of two PM steel and two PM aluminium alloys are examined. As the experimental basis, constant amplitude tests with different stress amplitudes and stress ratios (to determine the S–N curves and mean stress sensitivities) as well as service load tests (variable amplitude loading) were carried out. The fatigue life was calculated, applying different modifications of the linear damage accumulation. The results of the experiments and calculations were compared and statistically evaluated. Regarding the resulting scatter, the fatigue life assessment with the modified damage accumulation by Zenner and Liu is recommended. Furthermore, mean relative damage sums are derived, which can be used to correct the fatigue life calculation. For PM steel, these values are very similar to compact steels, whereas they are higher for PM aluminium.

Keywords:

• Structural integrity
• Concepts of fatigue life assessment
• Damage accumulation
• PM steel and aluminium
• Accuracy of fatigue life assessment

Acknowledgements

The project was funded by the German Federal Ministry of Education and Research within the framework of the ‘Wachstumskern Thale PM’. This support is gratefully acknowledged. Furthermore, the authors would like to thank Schunk Sintermetalltechnik from Thale, Germany, particularly Mrs S. Müller, for the support and the provision of the fatigue test specimens.