PSI - Issue 75

Tomáš Karas et al. / Procedia Structural Integrity 75 (2025) 150–157 T. Karas et al. / Structural Integrity Procedia 00 (2025) 000–000

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The self-heating method is based on the principle that materials generate heat when subjected to cyclic loading because of internal energy dissipation. This dissipation arises from two primary sources: internal friction, which is associated with anelastic and recoverable microstructural motions, and microplastic deformation, which involves plastic and non-recoverable movements at the defect level (Zaeimi et al. (2024)). The resulting temperature increase can be measured and correlated with the material’s fatigue behaviour. Luong (1998) and La Rosa and Risitano (2000) developed rapid fatigue limit estimation techniques that use the linear interpolation of measured stabilised temperature increases at di ff erent stress amplitude levels. These methods analyse the relationship between the applied stress amplitude and the resulting stabilised temperature increase. Huang et al. (2017) later reviewed various approaches to the fitting of curves to experimental thermographic data for fatigue limit evaluation. The relatively new and promising form of this method was designed by Matusˇu˚ et al. (2024) called LinExp method that utilises di ff erences in trends of the stabilised temperature increase caused by elastic e ff ects below the fatigue limit and by plastic e ff ects above the fatigue limit. Fretting fatigue involves a complex multiaxial stress state at the contact. Therefore, accurate multiaxial fatigue criteria are essential for predicting fatigue damage under fretting conditions. Nesla´dek et al. (2024) found that for 42CrMo4 + QT steel under fretting fatigue, the elastic-plastic Finite Element Analysis (FEA) solution is essential for good quality prediction, and the Papuga’s quadratic parameter criterion (QCP) performs best among various criteria coupled with stress gradient correction using the Theory of Critical Distances - TCD (Susmel (2009)). Although there is research on high cycle fatigue of 42CrMo4 + QT steel by Papuga et al. (2023) and its fretting fatigue behaviour studied by Nesla´dek et al. (2022) and Suchy´ et al. (2022), also with application of the self-heating method Matusˇu˚ et al. (2022), a significant gap remains in the direct utilisation of the self-heating method to charac terise fretting fatigue of this steel. Additionally, the e ff ect of di ff erent load ratios, R , on the self-heating response under fretting conditions has received limited to no attention. This study aims to address these gaps by investigating the applicability of the self-heating method for characterising fretting fatigue in 42CrMo4 + QT steel. The objective is to verify the possibility of replacing the conventional S-N curve measurement with the LinExp method. Furthermore, this research investigates the influence of two di ff erent load ratios ( R = − 1 and R = 0) on the self-heating response, fretting fatigue behaviour, and the evaluation of multiaxial criteria supported by fractography.

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Fig. 1. (a) Test sample; (b) Bridge type pad (r = 1 mm); (c) Single contact pad (r = 50 mm); (d) Sample and pads with high emissivity coating.