Comparing Reservoir and Outcrop Specimens for Mixed Mode I-II Fracture Toughness of a Limestone Rock Formation at Various Conditions

Investigation of proper specimen geometry for mode I fracture toughness testing with flattened Brazilian disc method

“…In this case, large compressive loading area in a specimen of relatively large size may be increasing the confining effect around the central part of the specimen where crack front is located. Confining pressure was reported to cause an increase in K Ic by Al-Shayea (2002).…”

Combined effects of increasing temperature and confining pressure on the fracture toughness of clay bearing rocks

“…They observed a decrease of fracture toughness above 100 C and claimed that it was due to the development of microcracks caused by differential thermal expansion between adjacent mineral grains. However Al-Shayea [6] reported that fracture toughness of limestone increased by about 25% at 116 C. Uniaxial compressive tests were carried out at temperatures of 75 C, 100 C, 125 C, and 150 C to investigate the variation of the initial tangent Young's modulus (Fig. 18).…”

“…However, it is essential that the measurements be carried out at elevated temperatures and pressures to simulate in situ conditions [6]. This paper presents the methodology for determining toughness using the SENRBB and SCB specimen configurations.…”

Mode ІІ fracture study of rocks using Brazilian disk specimens

“…The experimental values of K IIc /K Ic have been extracted using the average value of K Ic and K IIc reported in Refs. [1,[5][6][7]. Since the fracture toughness ratio K IIc /K Ic obtained experimentally from the CSTBD specimen was always higher than the estimated values of the MTS criterion, Ayatollahi and Aliha [23] proposed a new criterion called the GMTS criterion that takes into account the effect of T-stress in addition to the conventional singular stresses in the MTS criterion.…”

“…But many different test specimens have been proposed in the past for determining the mode II fracture toughness of rocks. Some of the wellknown test configurations are the centrally cracked Brazilian disk under diametral compression [1][2][3][4][5][6][7][8][9], the edge cracked semi-circular specimen subjected to three point bending [5,10,11], the single-edge crack specimen subjected to asymmetric four point bend loading [12][13][14][15] and the compact shear-tension specimen [16][17][18]. Among these specimens, the centrally cracked Brazilian disk (CSTBD) subjected to diametral compressive load has been recognized as a favorite test specimen for conducting mode II fracture toughness experiments on rocks because it can be easily extracted from rock cores.…”