13th International Conference on Fracture June 16–21, 2013, Beijing, China -7- Figure 6. The micro crack propagation path for S/Pd=10 edge angle ψ =60, Pd=6, mm and extended length of δ=4mm (8 iteration). In order to investigate the effect of erosion on the TBM, the results of modeling as illustrate in Figs. 7- 9. According to the Fig. 7, because the cutters are blunted under erosion, as a result, more specific energy for eroded cutters than non-eroded cutters is required. The figure shows that in both cases, the optimum ratio S/Pd is in range of 7.5–15, which is in well agreement with the experimental results. Figs. 8 shows comparison between eroded and non-eroded disc cutters for the Mode I and Mode II stress intensity factors, KI, KII (MPa m 1/2) versus different S/Pd ratios. Figs. 9 shows comparison between eroded and non-eroded disc cutters for the Mode I and Mode II stress intensity factors, KI, KII (MPa m1/2) versus different Pd ratios. Figure 7. Comparison between eroded and non-eroded disc cutters for specific energy SE (Mj/m3) versus different S/Pd ratios x y S Free surface AR1 AR2 AR3 AR4 ψ
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