PSI - Issue 13

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

530

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2. Materials and experimental procedure

2.1. Material

The material used for the vibration fatigue test in this study was A5056 aluminium alloy. Tables 1 and 2 list the chemical composition and mechanical properties of the A5056 aluminium alloy, respectively.

Table 1. Chemical composition of A5056 aluminium alloy (mass%). Si Fe Cu Mn Mg Cr

Zn

Al

0.05

0.12

0.01

0.08

4.92

0.06

0.02

Bal.

Table 2. Mechanical properties of A5056 aluminium alloy. 0.2% proof strength Tensile strength

Elongation

114 MPa

252 MPa

41.5%

2.2. Vibration fatigue testing

Figure 1a shows the shape and dimensions of the specimen for the vibration fatigue test. We employed button head-type specimens with a notch, as the stress is concentrated at the notch because of the vibration of the specimen head. Figure 1b shows the setup of the specimen, thermometer, and accelerometers on the shaking table. The multi axial random vibration experiments were performed at different acceleration inputs (10, 20, 30, 40, 50, 60, and 70 G rms ) within a frequency band of 10 – 5000 Hz under a nitrogen gas environment at 25 °C. The vibration test results show that the specimen did not break even after applying the vibration for 1 h at 70 G rms . Therefore, the weight, shown in Fig. 1c, was placed on the specimen head, and the vibration test was then carried out. The test results of this study were obtained for the specimens with the weight. After the vibration tests, we observed the fracture surfaces of the specimens using a scanning electron microscope (SEM).

Fig. 1. (a) shape and dimensions of the specimen for the vibration fatigue test; (b) setup of the specimen, thermometer, and accelerometers on the shaking table; (c) shape and dimensions of the weight for the vibration specimen.

3. Results 3.1. Vibration fatigue strength

Figure 2 shows the relationship between the applied gravitational acceleration and the time to failure of the A5056 aluminium alloy. In Fig. 2, the arrow indicates that the fracture had not occurred when the specimen was loaded for 1 h. The observation of the tests was speculated to be a resonant mode of the transverse bending of the head part in all specimens. In Fig. 2, as the gravitational acceleration decreases, the time to failure tends to largely increase. However, from 40 to 70 G rms , no significant difference in the time to fracture is confirmed. There is a similar tendency between 20 and 30 G rms . In other words, it is considered that factors other than the gravitational acceleration influenced the time to fracture.