PSI - Issue 13

Author name / Structural Integrity Procedia 00 (2018) 000 – 000

3

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

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2 ] and time to failure t [min].

Fig. 2. Relationship between applied gravitational acceleration G rms [m/s

3.2. Fracture surface

Figure 3 shows the surface of the specimen vibrated at a gravitational acceleration of 70 G rms . The test was interrupted just before the fracture. As shown in Fig. 3, a jagged crack is observed on the surface of the notch bottom. There are two possible reasons for this. One is the possibility that multiple cracks initiated and propagated, and finally coalesced. Another is that the cracks initiated and propagated while changing their propagation direction because of the multi-axial stress. Figure 4 shows the SEM image of the fracture surface of the specimen vibrated at a gravitational acceleration of 70 G rms . The specimen is the same as that shown in Fig. 3. As shown in Fig. 4a, the fatigue fracture surface due to the vibration loads and the dimple surface due to the tensile loads after the vibration test are confirmed. As the fatigue fracture surface exists in the opposite direction at the centre of the tensile fracture surface, it is considered that this specimen was mainly subjected to a unidirectional bending mode. Figs. 4b and 4c show striations on the fatigue fracture surface because of the vibration. As striations are observed along different directions, it is considered that the fatigue fracture could occur because of the propagation of multiple cracks and the coalescence thereof.

Fig. 3. Surface of the specimen vibrated at a gravitational acceleration of 70 G rms .