Assessment of remaining fatigue life based on temperature-evolution measurements

Assessing the remaining fatigue life of various engineering products is crucial to their long-term use. Temperature increases can be promising indicators of the remaining fatigue life since fatigue loading increases the material temperature. This study uses the cumulative temperature-increase method, in which fatigue failures are assumed to occur when the temperature increase in a material under fatigue loading accumulates up to a certain specific value. The conventional method fails to consider the temperature increases unrelated to fatigue damage; here, we attribute such increases to the viscoelastic behaviour (i.e. internal friction). To improve the estimation accuracy of the remaining fatigue life, the conventional method was modified to consider the non-fatigue-related temperature increases. Carbon steel bar specimens were subjected to torsional loading, and their remaining fatigue lives were assessed based on their cumulative temperature increases. Then, the accuracies of the modified and conventional methods were quantitatively evaluated in comparison with their actual remaining fatigue lives. The modified method could better estimate the remaining fatigue life than the conventional method, as evidenced by the lower average relative errors in the modified method compared with the conventional method. As the total cumulative temperature increase is affected by the loading history, future studies must clarify the influence of the loading history and consider it in the assessment of the remaining fatigue life.