Issue 33

Y. Wang et alii, Frattura ed Integrità Strutturale, 33 (2015) 345-356; DOI: 10.3221/IGF-ESIS.33.38 353 ' ' NP 1.25 K K   ' ' NP n n  Both the strain loading history and the stress loading history at the assumed crack initiation site are needed. If the stress loading histories were not given in the original sources, they were calculated by using the model proposed by Jiang and Sehitoglu [24]. In Fig. 4, the predicted fatigue lives are compared with the experimental ones for S45C steel and SNCM630 steel under VA multiaxial fatigue loading. Fig. 4 also shows the loading paths applied to specimens made of S45C steel and SNCM630 steel. As it can be seen from this figure, 81% of the data are within a scatter bands of 3. Data points under loading blocks with a considerable portion of axial loading such as AT, TA and AV are outside of the target scatter band, being on the conservative side. Material Ref. E (MPa) G (MPa) ν S45C [20] 186,000 70,600 0.28 SNCM630 [21] 196,000 77,000 0.273 1050 QT Steel [12] 203,000 81,000 0.27 304L steel [12] 195,000 77,000 0.27 Pure titanium [22] 112,000 40,000 0.4 Titanium alloy BT9 [22] 118,000 43,000 0.37 Table 1 : Elastic static constants for the considered materials. Material Ref.  ’ f  ’ f (MPa) b c  ’ f  ’ f (MPa) b 0 c 0 K’ (MPa) n’ K’ NP (MPa) n’ NP S45C [20] 0.359 923 - 0.099 - 0.519 0.198 685 -0.12 -0.36 1215 0.217 1519 0.217 SNCM630 [21] 1.54 1272 - 0.073 - 0.823 1.51 858 -0.061 - 0.706 1056 0.054 1320 0.054 1050 QT St. [12] 2.01 1346 - 0.062 - 0.725 3.48 777 -0.062 - 0.725 1461 0.06 1420 0.113 304L St. [12] 0.122 1287 - 0.145 - 0.394 0.211 743 -0.145 - 0.394 680 0.214 5056 0.373 Pure Ti [22] 0.548 647 - 0.033 - 0.646 0.417 485 -0.069 - 0.523 - - - - BT9 [22] 0.278 1180 - 0.025 - 0.665 0.18 881 - 0.0082 -0.47 - - - - Table 2 : Fatigue constants for the considered materials. Figure 4 : Comparison of observed and predicted fatigue lives by the MMCCM for S45C and SNCM630.