13th International Conference on Fracture June 16–21, 2013, Beijing, China -8Figure16. a- Ncurves of the case of axial pin-load Figure17. a- Ncurves of the case of 30° pin-load The a- Ndata are calculated by the seven points incremental polynomial method[16]. The SIF range value ΔKand da/dNcan be obtained by the fitted crack length value a*. Table 5 shows the data processing of the test piece No.1. Table 5. Data processing of the test piece No.1 N/(cycle) a/(mm) a*/(mm) da/dN ΔK/(MPa·m1/2) lg(da/dN) lg(ΔK) 0 1.539 2000 1.967 4000 2.276 6000 2.506 2.579 1.79E-7 26.556 1.424 -6.746 8000 2.958 2.927 1.85E-7 27.292 1.436 -6.732 10000 3.307 3.316 2.01E-7 28.026 1.447 -6.697 12000 3.767 3.752 2.14E-7 28.781 1.459 -6.669 14000 4.159 4.186 2.16E-7 29.497 1.469 -6.665 16000 4.652 4.629 2.24E-7 30.218 1.480 -6.649 18000 5.091 5.074 2.31E-7 30.956 1.490 -6.636 20000 5.503 5.543 2.43E-7 31.771 1.502 -6.614 21800 5.981 5.976 2.47E-7 32.577 1.512 -6.608 23000 6.291 6.278 2.59E-7 33.180 1.520 -6.585 24000 6.578 25000 6.756 26000 7.109 The da/dNdata of the other three test pieces can be obtained by the same method. The data points of region II are fitted by the least square method to get the lg(da/dN)~lg(ΔK) curve. Figure18 shows the fitted line of the data points. * ** * * * * * * * * * * * * * * ** * * * * * * ** * *** *** **** *** * * * * * * Fitted line Data points -6.4 -6.5 -6.6 -6.7 -6.8 lg(da/dN) l g (ΔK) 1.4 1.45 1.5 1.55 1.6 Figure 18. lg(da/dN)~lg(ΔK) curve of the axial pin-load case
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