Determination of size-independent fracture energy of granite using peak loads of beams

Abstract

Fracture energy, defined as the amount of energy necessary to create one unit area of a crack, is a very important parameter in analyzing the behavior of quasi-brittle materials such as concrete, mortar, rock, et al.. The size-independent fracture energy of concrete and mortar can be obtained according to boundary effect theory. The intention of this paper is to determine the sizeindependent fracture energy of granite by virtue of the peak loads of three-point-bending notched beams. An analytical model was presented to correlate the peak loads with the crack-tip local fracture energy in granite beams. A fracture test was then carried out on granite beams with two depths, i.e., 30 mm and 70 mm. For the beams with depths of 30 mm, the notches are cut with lengths from 3 mm to 18 mm. For the beams with depths of 70 mm, the notch lengths vary from 2 mm to 53 mm. The average value of the maximum tensile stress at the fictitious crack-tip is adopted as 8 MPa. Upon the comparison between the analytically predicted peak loads and the experimentally determined ones, the correlation between the crack-tip local fracture energy and notch length can be obtained. It can be found that the value of crack-tip local fracture energy almost keeps 300 N/m without free boundary effect for the notch lengths from 9 mm to 18 mm in the beams with depths of 30 mm and for the notch lengths from 10 mm to 53 mm in the beams with depths of 70 mm. Thus, the size-independent fracture energy is 300 N/m for this type of granite.