Probabilistic Scatter Band with Error Distribution for Fatigue Life Comparisons

Abstract

This paper presents a new probabilistic evaluation technique of fatigue life based on the adaptation of control chart concept incorporated in a scatter band. Conventionally, scatter band is a tool for visual evaluation of fatigue life accuracy. Such band is also used as an evaluation criterion for the estimation methods of fatigue strain–life equation. However, the current scatter band technique provides no probabilistic interpretation of the deviation that occurred during comparison. This technique is only used as a comparison tool considering whether the data points fall within or outside the predefined accuracy band. Therefore, a new framework of probabilistic scatter band is introduced in this study. The symmetrical tolerance interval with normal distribution is used to characterise the probabilistic field with upper and lower tolerance limit according to two standard deviations or a 95% tolerance limit. Using this technique, the comparison between fatigue life prediction and experimental data is provided in regions according to conservatism. The probability of error and rejection index values according to the statistical distribution of fatigue life is also presented. The proposed technique is applied in fatigue life evaluation between strain–life models and experimental data available in literature. The new technique is practically informative in probabilistic interpretation of fatigue life results with scatter and uncertainty factors included.