Issue 35

C. Gandiolle et alii, Frattura ed Integrità Strutturale, 35 (2016) 232-241; DOI: 10.3221/IGF-ESIS.35.27 240 For each loading block, ΔK eff is plotted as a function of depth in Fig. 10. Knowing crack lengths obtained at the end of each block from Fig. 9b, it is possible to shift from one curve to the other. At the end of the second bloc, crack length was equal to b 2 =170µm. and at this depth, ΔK eff (block 3) passes below the crack arrest threshold condition ΔK 0 =5.7MPa.m 1/2 . Combining these crack propagation paths evolutions, the final crack arrest condition achieved when these three loading sequences were imposed can be understood. Figure 10 : Evolutions of ΔK eff of each loading blocks as a function of depth. The predictive method was applied for the studied mixed load test condition. Eq. 10 is incremented step by step and depending on N, the relevant ΔK eff is considered. Fig. 11 plots the predicted crack propagation extension compared to the experimental crack propagation extension. Prediction is conservative as the predicted crack length is longer than the experimental crack length. However the predictive method recognizes the crack nucleation on the first block and the crack arrest at the third block. Hence even if the model tends to overestimate the final crack extension, it well predicts the fretting fatigue crack arrest condition. Figure 11 : Comparison of theoretical crack propagation rate calculated with the predictive method and experimental crack propagation rate. Loading: R=4.6mm, P, Block 1 : σ F,moy /σ y,flat =0.78, R σ =0.85, Q*/P=0.3, N=70000; block 2 : σ F,moy /σ y,flat =0.78, R σ =1, Q*/P=0.3, N=670000; block 3 : σ F,moy /σ y,flat =0.78, R σ =0.85, Q*/P=0.15, N=1000000.