13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- positive and the effect of other micro-arc oxidation ceramics coating technologies, such as micro-arc oxidation process and hard oxidation process, on the fatigue life of Al 2024-T4 alloy is negative. 2. Material and Experimental Procedure Materials used were Al 2024-T4 alloy and Al 7074-T6 alloy. And the size and shape of the experimental specimens is shown in Figure. 1 including the morphology of specimen with the different micro-arc oxidation ceramics coating processes consisting of the different micro-arc oxidation ceramics coating technologies with sealing hole, micro-arc oxidation ceramics coating and hard oxidation ceramics coating surface technologies as shown in Fig. 1b. The oxidation ceramics coating layer of all experimental specimens by the different oxidation ceramics coating surface technologies has the approximate same ceramics coating layer thickness of about 0.15 mm. The center notch in these specimens was fabricated to control the stress concentration factor as about 1.08. The mechanical properties of aluminum alloys are presented in Table 1. All fatigue tests were performed by using the rotating bending machine including the addition relative humidity controlled device and 4-spindle loading device (by Yamamoto Metal Tech Co. LYD, Japan) as shown in Figure 2. The machine provides the cyclic loads at the frequency of 50 Hz and at the stress ratio of R=-1. Table 1. Mechanical properties σ0.2 (MPa) σB (MPa) E (GPa) δ (%) Al 2024-T4 325 470 70.0 20 Al 7075-T6 527 673 72.2 11 σ0.2: 0.2% proof stress. σB: Tensile strength. E: Young’s modulus. δ: Percentage elongation. (a) (b) Figure 1 Shape and dimensions of specimens (mm) Figure 2 Experimental machine
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