13th International Conference on Fracture June 16–21, 2013, Beijing, China -6- ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ − + ⋅ = a R a R ffw 2 1 2 2 2 sec π , (29) ⎟ ⎟ ⎠ ⎞ ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ ⋅ ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ ⋅ ⎜ ⎜ ⎝ ⎛ ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ ⋅ ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ ⋅ = -5.1399 +9.9046 -6.0293 +1.6326 -0.1654 1 2 2 1 2 3 1 2 4 1 2 R R R R R R R R frr . (30) Scope of application： °≤ ≤ ° 45 5 β , 1.6 0.1 1 ≤ ≤ R a , 3 R R 1.5 1 2 ≤ ≤ , 20 5 1 ≤ ≤ R . 4. Fatigue crack growth test and residual esidual strength test 4.1 Test pieces Figure 11 shows the dimensional drawing of the straight attachment lug piece. There is a small slot made by electrical discharge machine (EDM) besides the lug hole with an angle of θ=90° or θ=60°. The slot length a0 is approximately equal to 1mm. The lugs pieces subjected to axial ( θ=90°) or 30 degrees oblique ( θ=60°) pin-load are all made of 30CrMnSiA material, 4 pieces for each case. R1 0 R2 2 .5 a0 Symmetry line 45 6 5 8 7 .5 θ Figure 11. Geometry of the test piece 4.2 Test equipments and loading requirement The tests are carried out on the material test system MTS-810 (load relative error <±2%) with a constant amplitude loading spectrum of sine waveform. The length of the crack is observed and measured by JXD-250mm scale microscope with a precision of 0.01mm. Surface around test piece’s wire-cutting slot tip is polished by a sand paper along the direction perpendicular to the slot direction. Peak load Ppp in the crack growth preparation test is 13.85KN, valley load Ppv is 0.83KN, R=0.06, load frequency is 5Hz. A crack with a length of 0.314mm was observed when fatigue cycle reaches about 15000, and grows to 0.612mm when 21000 cycles. The a- Ndata shows that the crack is growing steadily under the peak load of the fatigue crack growth test Pp=20.77KN and the valley load Pv=1.246KN. Table 2 shows values of the test load. Table 2. The test load values Case Ppp/(KN) Ppv/ (KN) Pp/(KN) Pv/(KN) θ=90° 13.85 0.83 20.77 1.25 θ=60° 13.85 0.83 20.77 1.25
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