The influence of the nonsingular stress term (T-stress), existing in the Williams expansion of the crack tip stress field, on the fracture behavior of the compressive-shear crack is comprehensively considered in this paper. According to the stress boundary conditions on the crack surfaces, the theoretical solution of the stress field around the closed crack tip is established using the complex potential theory, which includes not only the singular term containing the stress intensity factor KII but also three nonsingular terms (T-stress: Tx, Ty, and Txy) without KII. Then, the differences between tangential stresses and shear stresses at the crack tip obtained in the cases with and without T-stress are compared, respectively. Outcome indicates that there are tangential tensile stress and compressive stress zones at the crack tip when considering T-stress, while only the former exists when ignoring T-stress. In the case of considering T-stress, an improved crack initiation criterion is proposed, where the maximum tangential tensile stress and maximum shear stress are utilized simultaneously to predict the crack initiation and failure mode under the multiaxial compression stress state. Besides, the triaxial compression tests were carried out on the prismatic rock-like material samples with a central crack, and the effectiveness and validity of the proposed criterion are verified by comparing the experimental results and theoretical predictions. It reveals that the proposed criterion can reliably predict the crack initiation angles and failure modes with higher accuracy than traditional fracture criterion.

To investigate the influence of crack‐type defect and confining pressure on the mechanical properties of brittle materials, conventional triaxial compression tests were conducted on five types of prismatic samples with the same size of 41 mm × 70.7 mm × 175 mm at six confining pressures of 0, 5, 10, 20, 40, and 70 MPa, respectively. Among the five types of samples, one is intact, with uniaxial compressive strength of 140 MPa, and the other four are all defective and contain a single prefabricated crack with the length of 10 mm and the inclination angles of 0°, 30°, 60°, and 90°, respectively. All samples are made of reactive powder concrete with the same mix proportion. According to the test results, the following conclusions are obtained. (1) For any kind of defective sample and any confining pressure, relative values of the strength deviation that the defective samples deviating from the intact sample are all less than relative values of the strength range (max–min) of the five samples. (2) There exist two critical values p1 and p2 of the confining pressure p, the inclination angle of the prefabricated crack has significantly different impact on the compressive strength in the interval of 0 ≤ p < p1, p1 ≤ p < p2, and p ≥ p2, respectively.

Compression is a typical stress condition for cracks in deep-water structures, where the cracks tend to close from a nonclosed state, due to a certain gap that exists between the surfaces on both sides of cracks. The stress field models around the crack have been established in previous studies, while the crack surfaces are simply assumed in a nonclosed or full-closed state. In fact, the cracks inside deep-water structures are usually in a semiclosed state, leaving the reliability of calculation results in risk. To reflect the actual state of crack, a comprehensive stress field model around the semiclosed crack is established based on the complex potential theory, and the stress intensity factor K II at the crack tip related to the closure amount of crack surfaces, deep-water pressure, friction coefficient in the closed region, and crack inclination angle is derived. The analytical solution of the stress field around the semiclosed crack contains three T -stress components, i.e., T x , T y , and T x y . The rationality and effectiveness of the proposed stress field model are verified by the isochromatic fringe patterns around the crack obtained from the photoelastic experiment. It reveals that the proposed model can reasonably predict the evolution of the stress field with the closure amount of crack under constant and variable stress conditions.

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