PSI - Issue 68

Reza Afsharnia et al. / Procedia Structural Integrity 68 (2025) 1153–1158 Reza Afsharnia et al. / Structural Integrity Procedia 00 (2025) 000–000

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Figure 3. Testing setup (a) for fatigue tests and (b) for fracture mechanics tests.

4. Results Figure 4 shows the calculated maximum allowed stress amplitude for very high cycle fatigue (1e7) using Model I based on the fractur mechanics tests in longitudinal and transversal directions for the selected materials. Due to limitations in the available equipment, measuring the threshold stress intensity was not feasible. Consequently, a MATLAB code was developed to determine the optimum ∆ #$ , which is equal to or less than the threshold for a crack growth rate of 1e-7 mm/cycle , while minimizing the deviation between the calculated and measured stress amplitudes.

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Figure 4. From fracture mechanics (FM) calculated and measured stress amplitude for very high cycle regime in (a) longitudinal direction and (b) transversal direction for PPGF20 and PPGF40 The calculated optimum ∆ #$ for both materials in both longitudinal and transverse directions was approximately 1.12 MPa√m, which is lower than the threshold for a crack growth rate of 1e-7 mm/cycle. Figure 5 illustrates the normalized driven S-N curve derived from the fracture mechanics test data. Due to the variability in fiber length within the materials, which can be influenced by various parameters, a fixed value cannot