13th International Conference on Fracture June 16–21, 2013, Beijing, China -7- Some previous studies [1, 6] have indicated that, for the same 7xxx material, the plate and hand forging forms have the same composition, including particles and pores, but the grain aspect ratio and flow may be different near the surface. The hand forging shows more scatter in the crack growth rates; however, the average crack growth rates for both plate and forging are very similar to each other. Next, the developed NRC ‘residual stress free’ model, from the 7075-T73 forging tests, was used for fatigue life estimation of 7075-T73 plates. 1.E‐09 1.E‐08 1.E‐07 1.E‐06 1.E‐05 1.E‐04 1.E‐03 1.E‐02 1 10 100 da/dN (inch/cycle) K (ksi in) 7075 B‐4 (R=0.05; no ACR) 7075 B‐4 (R=0.05; with ACR) 7075 D‐1 (R=0.05; no ACR) 7075 D‐1 (R=0.05; with ACR) SENT results (R=0.05) NRC TL2 model (R=0.05) 1.E‐09 1.E‐08 1.E‐07 1.E‐06 1.E‐05 1.E‐04 1.E‐03 1.E‐02 1 10 100 da/dN (inch/cycle) K (ksi (in) SENT results (R=‐0.3) TL2 model (R=‐0.3) 1.E‐09 1.E‐08 1.E‐07 1.E‐06 1.E‐05 1.E‐04 1.E‐03 1.E‐02 1 10 100 da/dN (inch/cycle) K (ksi (in) 7075 A‐4 (R=0.45; no ACR) 7075 A‐4 (R=0.45; with ACR) 7075 E‐1 (R=0.45; no ACR) 7075 E‐1 (R=0.45; with ACR) SENT results (R=0.5) NRC TL2 model (R=0.5) NRC TL2 model (R=0.45) 1.E‐09 1.E‐08 1.E‐07 1.E‐06 1.E‐05 1.E‐04 1.E‐03 1.E‐02 1 10 100 da/dN (inch/cycle) K (ksi in) 7075 E‐3 (R=0.8; no ACR) 7075 E‐3 (R=0.8; with ACR) SENT results (R=0.8) NRC TL2 model (R=0.8) Figure 8. SENT and C(T) test results, and NRC (TL2) model for SENT (1-in=25.4 mm, 1.0 ksiin=1.1 MPam) da/dN(in/cycle) K or Kmax(ksi in) R = 0.05 R = -0.3 R = 0.5 R = 0.8 1.E-09 1.42 1.20 1.01 0.71 2.E-09 1.49 1.27 1.07 0.77 1.E-08 1.69 1.46 1.25 0.92 2.E-08 1.83 1.60 1.40 1.08 4.E-08 2.04 1.79 1.61 1.30 6.E-08 2.25 1.98 1.78 1.45 1.E-07 2.66 2.33 2.09 1.69 2.E-07 3.90 3.39 2.97 2.29 4.E-07 4.98 4.37 3.92 3.16 6.E-07 5.73 5.04 4.53 3.70 8.E-07 6.31 5.56 5.02 4.13 1.E-06 6.69 5.91 5.36 4.45 2.E-06 7.93 7.01 6.40 5.36 4.E-06 9.45 8.38 7.67 6.49 1.E-05 12.28 11.00 10.29 9.12 2.E-05 15.34 13.76 12.87 11.39 4.E-05 19.38 17.23 15.84 13.52 1.E-04 26.58 23.32 20.90 16.89 2.E-04 31.27 27.15 23.81 18.38 4.E-04 36.56 31.21 26.44 18.97 6.E-04 40.52 34.23 28.38 19.45 8.E-04 41.83 35.18 28.92 19.46 1.E-03 43.14 36.18 29.55 19.61 4.E-03 50.34 41.46 32.65 20.04 1.E-02 52.96 43.39 33.80 20.28 Figure 9. NRC combined material model for 7075-T73 (1-in=25.4 mm, 1.0 ksiin=1.1 MPam) 5. Fatigue crack growth life estimation 5.1. Coupon life estimation The NRC material model was used to estimate the crack growth lives of some 7075-T7351 plate R=0.05 R= -0.3 R=0.45-0.5 R=0.8 1.E‐09 1.E‐08 1.E‐07 1.E‐06 1.E‐05 1.E‐04 1.E‐03 1.E‐02 0.1 1 10 100 da/dN, dc/dN (in/cycle) K or Kmax (ksi in) R = 0.05 R = ‐0.3 R = 0.5 R = 0.8 No C(T) test available for R= -0.3
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