PSI - Issue 75

Mattias Clarin et al. / Procedia Structural Integrity 75 (2025) 467–473 Clarin et al. / Structural Integrity Procedia 00 (2025) 000 – 000

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3. Results and discussion 127 The residual stress measurements at positions A – D (Fig. 3) are summarised in Fig. 4, where mean values and 128 standard deviations are shown for each orientation. 129 The results show predominantly compressive residual stresses in the 0° orientation and tensile stresses in the 90° 130 orientation. Measurements in the 45° direction fall between these two, indicating a smooth transition between the 131 principal stress directions. The low standard deviations indicate good consistency between the different measurement 132 positions on the specimen. 133

134 Figure 4. Residual stresses measured in 4 different positions on a specimen in as-welded condition. Mean values presented 135 together with the standard deviation between the four positions. 136 137 The influence of initial overload on the fatigue life of welded specimens is presented in Fig. 5, where fatigue test 138 results are plotted in terms of applied stress range versus the number of cycles to failure. The specimens were tested 139 under different nominal overload conditions: 0% (reference), 25%, 50%, 75%, and 100% of the yield strength of the 140 material. The fatigue data indicate a clear beneficial effect of initial overload on the fatigue performance of the welded 141 joints. Specimens subjected to higher overload levels generally exhibited improved fatigue resistance, characterised 142 by higher cycles to failure at given stress amplitudes compared to those without overload. The mean S-N curves, 143 determined by linear regression on the log-log scale, clearly illustrate the trend, with increased fatigue life observed 144 as the overload percentage increases. Tab. 1 summarises the parameters of these regression analyses, providing the 145 slope (m) of the fitted curves and mean fatigue strengths at 2 million cycles.

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Figure 5. Fatigue testing results for specimens without and with different levels of overloading prior to the fatigue testing.