PSI - Issue 13

Wenbo Sun et al. / Procedia Structural Integrity 13 (2018) 1020–1025 Author name / Structural Integrity Procedia 00 (2018) 000–000

1022

3

0°

45°

90°

Fig. 2. Building directions of specimen

3. Experimental setup Fatigue crack growth rate test was performed on MTS 810 fatigue testing machine, as shown in Fig. 3. According to the results of Ti-6Al-4V titanium alloy tested by Yong [14], the fatigue crack growth rate of 0° and 90° samples has different stress intensity factor transition point, T K  , which is 11.3 MPa m and 10.3 MPa m , separately. So 10 K MPa m   was chosen in this test. K  can be calculated by the formulation as followed.       2 3 4 3 2 2 0.886 4.64 13.32 14.72 5.6 1 K P B W                (1) where a W   . And then the stress level and stress amplitude of fatigue load are determined according to Eq.1.Fatigue R ratio is 0.1 and the maximum load P max is 5.19KN. The frequency is 20Hz. The crack was monitored with the QM413T digital microscope. The crack length was recorded per 10000 cycles at the beginning, and then per 2000 cycles when in the high K  regime.

Figure 3. Experimental setup

4. Results 4.1. Fatigue Crack Growth Rates

The crack growth rate test was completed, and the - a N curves were obtained and shown in Fig. 4. It is obvious that the - a N curves of 0° and 90° building direction samples appears similar, and the fatigue life of 45° specimen is longer. The fatigue crack growth life of 45°specimen is 1.46 times longer than that of 0° building direction specimen, shown in Table 1.