Abstract
To study the tensile and fracture properties of the specimen under the quasistatic loading, the Brazilian disc splitting method and the notched semicircular bend (NSCB) method were used to test the tensile properties of coal specimens, and the fracture properties of NSCB specimens with different notch depths were tested and analyzed. The applicability of plane strain fracture toughness KIC and J-integral fracture toughness in evaluating the fracture properties of coal specimens was discussed. The influence of notch depth on the fracture toughness measurement of the NSCB specimen was studied. Combined with the surface strain monitoring of specimens during loading and the industrial CT scanning image of damaged specimens, the deformation characteristics of coal specimen under loads and the distribution law of crack after failure were analyzed. The results show that the NSCB test is suitable for measuring the tensile strength of a coal specimen; when the dimensionless notch depth is β = 0.28, the dispersion of plane strain fracture toughness KIC of the NSCB specimen is the smallest. Besides, the plane strain fracture toughness of coal is obviously affected by the notch depth and dimensionless stress intensity factor. The J-integral fracture toughness can be used to effectively evaluate the fracture performance of specimens.
Highlights
To study the tensile and fracture properties of the specimen under the quasistatic loading, the Brazilian disc splitting method and the notched semicircular bend (NSCB) method were used to test the tensile properties of coal specimens, and the fracture properties of NSCB specimens with different notch depths were tested and analyzed. e applicability of plane strain fracture toughness KIC and J-integral fracture toughness in evaluating the fracture properties of coal specimens was discussed. e influence of notch depth on the fracture toughness measurement of the NSCB specimen was studied
Previous studies have found that the tensile strength of rock specimens measured by BD tests is about 0.63 times of that measured by the direct tensile method [29]. erefore, the tensile strength of specimens measured by SCB tests in this paper is about 0.76 times of that measured by the direct tensile method
The tensile strength of specimens measured by SCB tests is closer to that measured by the direct tensile test
Summary
Received 27 January 2021; Revised 10 February 2021; Accepted 19 February 2021; Published 26 February 2021. E results show that the NSCB test is suitable for measuring the tensile strength of a coal specimen; when the dimensionless notch depth is β 0.28, the dispersion of plane strain fracture toughness KIC of the NSCB specimen is the smallest. To measure the fracture toughness of mode I rock materials, the International Society for Rock Mechanics (ISRM) recommends four types of specimens: short rod (SR), chevron bend (CB), cracked chevron notched Brazilian disc (CCNBD), and notched semicircular bend (NSCB) specimens [12]. The analysis of crack propagation characteristics and the influence of notch depth in the fracture toughness test of rock materials using the NSCB specimens is still limited. In the fracture toughness test of BD, SCB, and NSCB specimens, strain gauges were set at different positions on the surface of specimens for deformation monitoring. In BD specimens, 1#–4# strain gauges were arranged at equal intervals (6 mm) from the center of the specimen to the lower boundary; in SCB specimens, only one group of strain gauges were set radially at the center of the bottom surface to record the tensile strain changes; in NSCB specimens, two groups of strain gauges were arranged on the line connecting the upper loading point and the notch, the distance between the center of 1# strain gauge and the loading point was 2 mm, and the distance between the center of 2# strain gauge and the end of the notch was 1.5 mm
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
