13th International Conference on Fracture June 16–21, 2013, Beijing, China -6- 4.2. SSM method results By using the dimensionless geometric parameter ( αS , 0α , 1α and αB ) and substituting into equation (3), SSM model predicts the value of 3.541 for minimum dimensionless stress intensity factor, which is 2.7% lower than the value obtained from the experimental data (see Fig. 5). Also note that I Y is the dimensionless stress intensity factor of the SCB specimen with a straight crack. Here, equation (2) was used for calculating I Y . Figure 5. slice synthesis method utilized for estimating min * Y in CCNSCB specimen Because of the convenience and accuracy of SSM, this method can be suggested as a reliable method for evaluating the minimum dimensionless stress intensity factor ( * min Y ) in the CCNSCB specimens. 5. Conclusions Although the SCB specimens with straight crack front have been used frequently by researchers, very few studies have been reported on the use of CCNSCB specimen in rock fracture toughness testing. The minimum dimensionless stress intensity factor of CCNSCB was calculated using SSM and its accuracy was assessed experimentally and by finite element method. Figure 6. Fracture surface of CCNSCB specimen Under mode I loading, a V-shaped (chevron) crack results in the automatic formation of a sharp and
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