PSI - Issue 77

210 Jafar Amraei et al. / Procedia Structural Integrity 77 (2026) 207–214 Author name / Structural Integrity Procedia 00 (2026) 000–000 Fatigue experiments were carried out using a custom-built shaker-driven cantilever bending setup operating in displacement control at a stress ratio of = − 1 . The electrodynamic shaker applied sinusoidal loading in the frequency range of 20–50 Hz with a step of 10 Hz, covering both increasing amplitude tests (IATs) and constant amplitude tests (CATs). The applied bending stress was calculated as: = 6 2 , (8) where is the maximum applied force, the span length, the specimen width, and the specimen thickness. Surface temperature evolution during fatigue was monitored using the infrared camera (InfraTec® VarioCAM®), while acoustic emission (AE) signals were recorded simultaneously with the Vallen® AMSY-5 system. To ensure reliable emissivity, specimens were coated with a black matte enamel. Two regions of interest (ROIs) were defined on the specimen surface to assess the global and localized thermal response, with the maximum temperature consistently observed near the fixed end. Full details of the material specifications and testing procedures can be found in (Amraei and Katunin, 2025). 4. Results and discussion 4.1. Frequency dependence of fatigue strength The first step in the fatigue life prediction framework includes determining the variation of fatigue strength with loading frequency. Fig. 1 presents the values obtained at 20, 30, 40, and 50 Hz using the bilinear approach from the previous study of the authors (Amraei and Katunin, 2025), in which the temperature-dependent heat capacity was considered to enhance the accuracy of the results. These experimentally validated values were then used to establish the exponential regression of the form =417.6e −0 . 0208 shown in Fig. 1, enabling the prediction of fatigue strength across the broader frequency range of 10–100 Hz. The results presented in Fig. 1 vividly depict that fatigue strength decreases exponentially with increasing frequency. This trend highlights the progressively stronger role of self-heating at higher loading frequency, which accelerates the transition from friction-dominated to damage dominated processes. 4

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Fig. 1. Fatigue strength versus loading frequency for the polymer-matrix composite, based on the data obtained from approach by taking into account temperature-dependent (Amraei and Katunin, 2025), with exponential regression for 10–100 Hz.