تأثیر تنش متوسط بر طول عمر فرسودگی
Abstract
1-Introduction
2-Material and testing condition
3-Experimental results and discussion
4-Conclusion
Acknowledgements
References
Abstract
An experimental investigation of the effect of mean stress on the fatigue life and corrosion fatigue life of cylindrical specimens is presented. Force controlled constant amplitude axial fatigue tests in the regime of 105 to 107 cycles were conducted for two different environments: in air (without corrosion) and in-situ in a corrosive environment, 0.824% NaCl aqueous solution flow. The test results are assessed with respect to various standard models of mean stress influence on fatigue. The reduction in material fatigue strength due to the corrosion environment is evaluated and the results obtained show that in a low salinity aqueous corrosive solution, the fatigue strength at 4×106 is reduced of a factor of 2 compared to no corrosion tests.
Introduction
Corrosion fatigue failure is relevant many industrial fields, including the mining industry, where pump components are design to operate under cyclic loading in corrosive environments. The effect of mean stress in such components is of high importance in the design process, as it can significantly influence fatigue strength. Low carbon steel is widely used in the mining industry because its cost and mechanical properties. The main problem with this material is that is affected by environmental conditions and is susceptible to corrosion. Many studies have been conducted to understand how corrosive environments affect fatigue life of steel [1] and how the corrosion fatigue strength of the material decreases. Usually, sea water conditions are tested and many data are available in literature relevant to this condition. However, other corrosive environments have received less attention in research and, consequently, less data are available. This study considers corrosion fatigue behavior in a fresh water environment. The effect of mean stress on fatigue life is a long established research topic. Several models have been proposed to describe its effects of the on the fatigue limit and more generally on material fatigue strength [2-6]. Several comparison of these different methods have been done to understand which of them better predicted the material behavior and many materials, including low alloy steel, have been compared [7,8]. However, the effect of corrosion has not been taken in account in these models. Recently some workers have studied the effect of mean stress on crack propagation in corrosive environment but in these investigations the stress-life approach is not considered.