Study of mixed mode fracture toughness and fracture trajectories in gypsum interlayers in corrosive environment

Abstract

Based on the engineering background of water dissolving mining for hydrocarbon storage in multi-laminated salt stratum, the mixed mode fracture toughness and fracture trajectory of gypsum interlayers soaked in half-saturated brine at various temperatures (20°C, 50°C and 80°C) were studied by using CSNBD (centrally straight-notched Brazilian disc) specimens with required inclination angles (0°, 7°, 15°, 22°, 30°, 45°, 60°, 75°, 90°) and SEM (scanning electron microscopy). The results showed: (i) The fracture load of gypsum specimens first decreased then increased with increasing inclination angle, due to the effect of friction coefficient. When soaked in brine, the fracture toughness of gypsum specimens gradually decreased with increasing brine temperature. (ii) When soaked in brine, the crystal boundaries of gypsum separated and became clearer, and the boundaries became more open between the crystals with increasing brine temperature. Besides, tensile micro-cracks appeared on the gypsum crystals when soaked in 50°C brine, and the intensity of tensile cracks became more severe when soaking in 80°C brine. (iii) The experimental fracture envelopes derived from the conventional fracture criteria and lay outside these conventional criteria. The experimental fracture envelopes were dependent on the brine temperature and gradually expanded outward as brine temperature increases. (iv) The size of FPZ (fracture process zone) was greatly dependent on the damage degree of materials and gradually increased with increase of brine temperature. The study has important implication for the control of shape and size of salt cavern.

A micromechanics-based variational phase-field model for fracture in geomaterials with brittle-tensile and compressive-ductile behavior

“…The loading mode is characterized by the stress intensity factors K I and K II through the mixity parameter A key observation is that, in all cases shown in figure 13, the resulting fractures are tensile. Thus, mode I fracture is predicted by the model for all loading modes, with fracture patterns in agreement with both numerical and experimental observations reported in the literature [130][131][132][133]. Figures 14,15,and 16 show the fracture process for β 0 = 0 • , β 0 = 27 • , and β 0 = 90 • , respectively.…”

“…As a consequence, the GMTS criterion takes into account the effect of both the T -stress and the fracture process zone. For pre-cracked Brazilian splitting tests, it has been shown experimentally [129,130,132] and numerically [133] that the MTS criterion strongly overestimates the initial crack propagation angle, while the GMTS criterion provides a much better agreement. Therefore, it is interesting to verify if the present model agrees with these observations.…”

“…Having shown the ability of the proposed model to describe shear fracture, we now turn our attention to the occurrence of tensile fracture under mixed-mode loading conditions. For this purpose, we consider centrally cracked Brazilian disk specimens subjected to diametral compression, representing benchmark experiments in rock-like materials [127][128][129][130][131][132][133]. Particular emphasis is put on the crack propagation angle with respect to the initial flaw, as typically studied in problems of this type.…”

Experimental Study of the Microstructural Evolution of Glauberite and Its Weakening Mechanism under the Effect of Thermal-Hydrological-Chemical Coupling

“…For example, when immersed for 30 h, the porosity in pure water at 80 • C were 2.59 times higher than that of half-saturated brine, and were 2.90 times higher than that of saturated brine. The comparison strongly confirmed that the chloride ion had an inhibitory effect on sodium sulphate dissolution, and the phenomenon could be explained by the Debye-Huckel theory, namely, sodium chloride was a symmetrical electrolyte [30][31][32][33]. When the concentration of sodium chloride solution was increased, the activity coefficient of calcium sulphate decreased and calcium sulphate formed ion pairs.…”

Mode I Fracture Toughness Test and Fractal Character of Fracture Trajectory of Red Sandstone under Real-Time High Temperature

“…According to the previous studies, it is widely recognized that fracture modes can be classified into 3 categories: transgranular fracture, intergranular fracture, and mixed fracture, which can be presented on the surface of the specimen. According to the research results of Zuo et al [1][2][3][4], it can be concluded that the roughness of the fracture surface after fracture is a comprehensive reflection of its microstructure, a magnitude of load and temperature [47,48]. erefore, the fracture trajectory is closely related to the roughness of the rock mass structural surface [49][50][51][52][53].…”