13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- comparing these methods are provided in Figure 2 for an example coupon (No. H2, R=0.6). This figure shows large differences between the KApp (ΔKeff-ACR in the figure) and other Keff results at the near-threshold region. The ΔKeff-2/ results are close to the ΔKACR whereas the ΔKeff-OP results are lower than others, and the ΔKeff-OP method is deemed to over-compensate the near-threshold data. App ACR ACR K = U K 0i 0 0i s si 0i ACR C C C C C C U ΔKApp is the full range, applied stress-intensity factor Coi/Csi compensates for a possible bias in the secant or open-crack compliances because of signal conditioning noise or nonlinearity Figure 1. Schematic of force-displacement curve showing critical parameters for ACR method (based on [2]) 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 da/dN (inch/cycle) ΔK (ksi in½) R=0.6 H2 ΔKapp ΔKeff‐ACR ΔKeff‐OP ΔKeff‐2/ Figure 2. Typical crack growth rate results (coupon H2, R=0.60) (1-in=25.4 mm, 1.0 ksiin=1.1 MPam) 1.E‐10 1.E‐09 1.E‐08 1.E‐07 1.E‐06 1.E‐05 1.E‐04 1.E‐03 1.00 10.00 da/dN (inch/cycle) ΔKapp(ksi in) R = 0.05 B4 D1 R = 0.33 E4 H1 I6 R = 0.45 A4 E1 R = 0.60 A3 H2 R = 0.80 E3 1.E‐10 1.E‐09 1.E‐08 1.E‐07 1.E‐06 1.E‐05 1.E‐04 1.E‐03 1.00 10.00 da/dN (inch/cycle) ΔKACR(ksi in½) R = 0.05 B4 D1 R = 0.33 E4 H1 I6 R = 0.45 A4 E1 R = 0.60 A3 H2 R = 0.80 E3 (a) da/dN-KApp (before ACR correction) (b) da/dN-KACR (after ACR correction) Figure 3. C(T) test results at R=0.05,0.33,0.45,0.60,0.80 (1-in=25.4 mm, 1.0 ksiin=1.1 MPam) W=2.0‐in Force, P Displ. V
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