PSI - Issue 42

Lucas Carneiro Araujo et al. / Procedia Structural Integrity 42 (2022) 163–171 Lucas Carneiro Araujo/ Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 1. Comparison of fatigue data of smooth specimens and Findley’s model predictions. The predictions of Findley and MWCM critical plane criterion, calibrated with and , form a fatigue limit curve as a function of values associated with loading conditions. This curve is shown in the graphs as a solid line, which divides the safe and failure region. Experimental data falling above this curve is expected to belong to failed specimens and those falling below to belong to run-outed specimens. Full markers refer to specimens that failed, whereas empty ones correspond to those that reached the run-out. The dashed lines represent error bands. In Fig. 1 the prediction line of Findley’s model against the experimental data are presented. The diagrams depict the shear stress amplitude ( ) against the maximum normal stress ( , ) variables that define the model. It is possible to observe that the model begins to predict well the fatigue strength with an error band of 30%, for all loading conditions. And that the current prediction is conservative, because it is predicting failures where run-outs are happening. The comparison between fatigue data and the MWCM predictions are in Fig. 2. The values of , and , used in the MWCM model are calculated as proposed by Araújo et al. (2011)[20]. To compute the critical plane for the MWCM, they first determine a range of candidate planes where the shear stress amplitude is equal or higher than 99% of the value of the maximum . Among these candidate planes, the critical will be the one containing the highest maximum normal stress, , . The predictions are also conservative. But different of Findley’s predictions for the uniaxial and in phase loading data the MWCM begins to predict well the fatigue strength with an error of only 20%.

Fig. 2. Comparison of fatigue data of smooth specimens and MWCM predictions.

The same comparisons will henceforward be made but now for the data from the specimens with the micro hole of 550 μ m. Fig. 3 show the data of specimens with micro hole and the Findley ’s model prediction, which maintains a conservative trend. But now for uniaxial and in-phase data the error for better predictions has decreased to 20%. For out-of-phase data, it remained at 30%.