A Study on Fatigue Strength Evaluation of Cast Steel under Variable Stress Conditions

Abstract

In this study, evaluation method for fatigue strength of cast steel under variable stress amplitude conditions in addition to constant stress amplitude condition was investigated. Fatigue tests were carried out using round bar specimen of SCW480 cast steel. As the experimental results, fatigue strength property was greatly sensitive to the intrinsic flaws of cast steel and stress patterns and it was difficult to determine fatigue evaluation curve using conventional S-N curve. Therefore, the predicted fatigue limit of flawed material, which was obtained based on threshold condition of small crack growth, was used as the parameter considering the intrinsic flaw size in order to eliminate the effect of the flaws to fatigue strength property. From S-N curve modified by the predicted fatigue limit, it was found that there was little variability in fatigue strength property. In addition, variable stress amplitude test results showed shorter fatigue life and constant and variable stress amplitude test results were determinately separate. Their plots could be represented by different two curves and fatigue evaluation curves considering variable stress amplitude conditions could be obtained without depending on not only the intrinsic flaw size but also variable stress patterns.