13th International Conference on Fracture June 16–21, 2013, Beijing, China -74.3 Fatigue crack growth test Figure 14 & Figure 15 show the experimental scene. Figure 14. Experimental field of the case of θ=90° Figure 15. Experimental field of the case of θ=60° The micro objective is aimed at the wire-cutting slot tip for detecting the fatigue crack in time. The frequency is changed to 1Hz every other 1000~2000 cycles in order to observe the crack length and record the a- Ndata. 4.5 Residual strength test After obtaining enough a- Ndata, the test pieces with different residual fatigue crack lengths are loaded with a sustained increasing load till the test pieces fracture, the corresponding residual strength data are recorded in Table 3 & Table 4. Table 3. The residual strength test results of the lugs subjected to axial pin-load test piece num. No.1 No.2 No.3 No.4 crack length a/(mm) 7.109 8.127 8.972 10.115 residual strength P/(KN) 91.456 83.242 78.051 72.947 Table 4. The residual strength test results of the lugs subjected to 30 degrees oblique pin-load test piece num. No.1 No.2 No.3 No.4 crack length a/(mm) 10.58 10.99 11.45 9.98 residual strength P/(KN) 58.54 42.38 40.24 58.8 The data of crack length aand corresponding residual strength Pin Table 4 & Table 5 are used to substitute the a&Pin formula (15) and formula(22) to calculate the SIFs. The SIFs of the axial pin-load case are: 164.30, 162.47, 166.37, 184.04, while the other case’s SIFs are: 214.91, 162.08, 171.77, 179.69, the unit is m MPa⋅ . As the fracture toughness of the material 30CrMnSiA with thickness 6.7mm is around 180 m MPa⋅ [16], it shows the SIFs calculated by formula (15) and formulas (22) are consistent with the true values. 5. Establishment of the fatigue crack growth model The fatigue crack growth data are fitted by using least square method, the curves are shown in Figure16 and Figure 17.
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