PSI - Issue 13

Junji Sakamoto et al. / Procedia Structural Integrity 13 (2018) 529–534 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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Second, a random vibration analysis was performed using the modal analysis results to calculate the stress acting on the specimen and its frequency. The bottom of the specimen was subjected to the PSD of the gravitational acceleration in the x, y, and z directions determined based on the experimental values, as shown in Fig. 6. Figure 7 shows the input values of the PSD of the gravitational acceleration in the x, y, and z directions, i.e., 10, 30, and 70 G rms , in the finite element analysis. Table 3 lists the stress distribution calculated using the finite element analysis for each gravitational acceleration value. The stress distribution is calculated as a normal distribution, and  is the standard deviation in the normal distribution, indicating the possibility of entering each stress region and its maximum stress value. Moreover, at the notch of the specimen, the frequency at which the maximum PSD of the stress was loaded was approximately 30 Hz. It is assumed that three stages of stress are loaded at the calculated ratio using the stress distribution, and the fatigue life is calculated using the modified Miner’s law. We assumed that 68.3% of the total load number was loaded with a stress amplitude of 1  ; 27.2% of the total load number was loaded with a stress amplitude of 2  ; 4.3% of the total load number was loaded with a stress amplitude of 3  ; and 0.2% of the total load number was loaded with a stress amplitude of 0. Figure 8 shows the S - N curve obtained by Patlan et al. (2001), and it is used for the modified Miner’s law. T he fatigue life at 10 G rms was calculated to be 1.16 × 10 7 cycles. When the fatigue life was converted into time using the calculated frequency, it was found to be 6430 min. As the specimen did not fracture in 60 min at 10 G rms , the analysis result is not inconsistent with the experimental result. Therefore, in the high cycle region where the stress is relatively low, the possibility of prediction using the finite element analysis remains to be seen. In the future, the stress and/or strain and the actually applied frequency should be measured.

Fig. 6. Experimental results of PSD of G rms : (a) y direction; (b) x and z directions.

Fig. 7. Input values of PSD of G rms in finite element analysis: (a) y direction; (b) x and z directions.