Abstract
To analyze the effect of the width of a prefabricated crack on the dimensionless stress intensity factor of notched semi-circular bend (NSCB) specimens, ABAQUS software was employed to perform numerical calibration of the crack tip stress intensity factor for the width of prefabricated cracks in the range of 0.0∼2.0 mm. The relative errors of the dimensionless stress intensity factor for different widths of prefabricated cracks were analyzed. The results indicate that the dimensionless stress intensity factor shows an approximate linear increase as the width of the prefabricated crack increases. The longer is the length of the prefabricated crack, the “faster” is the increase in speed. The effect of the dimensionless support spacing on the increase in the speed of the dimensionless stress intensity factor due to the increase in crack width is minimal. When the prefabricated crack width is 2.0 mm, the maximum relative error of the dimensionless stress intensity factor is 4.325%. The new formula for the dimensionless stress intensity factor that eliminates the influence of the width of a prefabricated crack is given, which provides a theoretical basis for the more accurate fracture toughness value measured using an NSCB specimen.
Highlights
Rock mass is a typical noncontinuous natural medium, whose interior presents many defects, such as joints and cracks [1, 2]
Such as diametrally compressed ring (DCR) specimen [9], cracked straight-through flattened Brazilian disk (CSTFBD) [10], edge cracked triangular (ECT) specimen [11], and edgenotched disc bend (ENDB) specimen [12,13,14]. e notched semi-circular bend (NSCB) specimen is a new type of specimen employed in static fracture toughness tests, which was recommended by International Society for Rock Mechanics (ISRM) in 2014. is specimen was proposed by Chong and Kuruppu [15] and has been extensively employed in fracture toughness tests due to its simple structure, ease of specimen preparation, and loading [16,17,18,19,20,21,22,23,24]
Based on the equivalent region integration method, the J-integral at the crack tip is obtained by ABAQUS software, and the stress intensity factor of the mode I crack is calculated by the following formula:
Summary
Rock mass is a typical noncontinuous natural medium, whose interior presents many defects, such as joints and cracks [1, 2]. In the calculation of fracture toughness by most researchers, the dimensionless stress intensity factor was obtained by substitution in the relevant formula recommended by the ISRM. The study which regards the influence of width of the prefabricated crack on the stress intensity factor is primarily focused on a disc-type specimen or three-point bending beams. Analysis of the extent to which the width of the prefabricated crack influences the dimensionless stress intensity factor is necessary to improve the method that measures the fracture toughness of NSCB specimens. For this reason, the dimensionless stress intensity factor of the crack tip was calibrated by ABAQUS software for different widths of the prefabricated cracks of the NSCB specimens in this paper. It is worth pointing out that it is not easy to prefabricate a crack on rock, and the crack tip of the manually prepared specimen is not an ideal sharp type, but a U-shaped crack with a certain radian. erefore, the numerical research work in this paper is to treat the prefabricated crack into a U-shaped crack, which is consistent with the actual crack form in the specimen used by researchers to test rock fracture toughness
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