Experimental Study on Damage Behavior of Rock in Compression–Tension Cycle Test Using 3D Digital Image Correlation

Excerpt

Understanding the mechanical properties of rock is essential for rock engineering, and uniaxial compressive strength (UCS) is the most widely used index for rock properties. Many scholars have investigated rock behaviors in the uniaxial compression condition under different stress paths, such as monotonous loading (Pepe et al. 2017; Taheri and Munoz 2016; Xue 2015), cyclic loading (Meng et al. 2018; Munoz and Taheri 2017; Song et al. 2016), and constant loading (creep or relaxation) (Hashiba and Fukui 2016; Okubo et al. 1991, 2010). Furthermore, tension properties are as important as compression properties to estimate the stability of rock structures. Although a direct tension test is difficult to conduct, some research results have been reported. Okubo and Fukui (1996) obtained complete stress–strain curves of different types of rocks based on a new control method. Yang et al. (2015) investigated the damage mechanisms of granite under uniaxial tension using the digital image correlation (DIC) method. Hashiba and Fukui (2015) considered the effect of water on the tension deformation and failure of rock. However, published data on the deformation of rocks under cycles between tension and compression are scarce because the test technique is complex and the operation is time-consuming. Mixed stress states exist in many situations in rock engineering, e.g., around underground openings in massive rocks, mine roofs in layered strata, hydraulic fracturing, rock cutting, and wellbore stability analysis (Stimpson and Chen 1993). Hereafter, we call the loading cycles between tension and compression as the C/T cycle test when compression is conducted first followed by complete unloading, which is then reversed to tension followed by complete unloading. The inverse of this loading sequence test is called the T/C cycle test. Hawkes and Mellor (1970) and Hawkes et al. (1973) conducted C/T cycle tests and investigated the deformation of three types of rocks but with relatively low applied stresses. Stimpson and Chen (1993) conducted T/C cycle tests to study the elastic modulus, but the specimen shape and test operation were very complex. Yu et al. (2005) conducted T/C cycle tests for four types of rocks with few cycles. …