Abstract
A stress analysis of a circular hole is one of the classical problems in mechanics. Internal cracks are inherent properties of materials, and they are mostly three-dimensional in form. However, studies on hole problems with three-dimensional internal cracks are still lacking. In this paper, internal cracks were generated in brittle materials containing circular holes based on 3D internal laser-engraved crack technology. Then, uniaxial compression tests were performed. The experimental results were compared with the existing literature, and theoretical and numerical simulation studies were carried out. The results show that: (1) The main crack shapes are the primary cracks and remote cracks. (2) The dynamic fracture characteristics existed in the formation of primary cracks and the surface of remote cracks. The tips of primary cracks were arc-shaped, and the surfaces of the remote cracks were curved. Remote cracks were tangential to the orifice where type III spear-like characteristics appeared. (3) The stress birefringence technology can be combined with 3D internal laser-engraved crack technology for internal crack stress information monitoring, the moire around the orifice was “flamboyant”, and the moire at the tip of the prefabricated crack was “petallike”. (4) The existence of internal cracks reduced the cracking and breaking load of the specimen, and compared with the intact orifice specimen, the upper primary crack, the lower primary crack, the remote crack and the failure load were reduced by 41.2%, 31.7%, 15.9%, and 32.3%, respectively. (5) The results of qualitative stress analysis of the orifice specimen were consistent with the initiation law of primary cracks and remote cracks. The K distribution based on M integral and the numerical simulation of crack propagation process based on the maximum tensile stress criterion were consistent with the law of primary crack growth. Compared with the current mainstream method of transparent rock research, 3D internal laser-engraved crack technology has certain advantages in terms of brittleness, crack authenticity, stress field visualization, and fracture characteristics, and the result will provide experimental and theoretical references for research on three-dimensional problems and internal cracks in fracture mechanics.
Highlights
The stress and failure analysis of circular holes is one of the classical problems in the mechanics, for example, the orifice fatigue fracture problems in aviation field [1,2,3]; the stress concentration problems of orifice bolts in mechanical engineering [4,5,6]; the problems of perforating hydraulic fracturing in oil and shale gas extraction [7,8,9]; the stability of surrounding rock of tunnels in hydraulic and geotechnical fields [10,11,12]
The K distribution based on M integral and the numerical simulation of crack propagation process based on the maximum tensile stress criterion were consistent with the law of primary crack growth
Lamé et al [13] gave a theoretical solution of a ring subjected to uniform internal and external loads based on the linear elasticity theory, which later became the basis of inelastic orifice problems; Muskhelishvili et al [14] used the plane elastic complex function method to give the expression for the stress field and displacement field of the orifice problem; Lv et al [15] and Fan et al [16] obtained the analytical expression of an orifice with arbitrary shape by deriving the orifice mapping functions; Mendelson et al [17] extended the elasticity problem of planar orifices to elastoplasticity
Summary
The stress and failure analysis of circular holes is one of the classical problems in the mechanics, for example, the orifice fatigue fracture problems in aviation field [1,2,3]; the stress concentration problems of orifice bolts in mechanical engineering [4,5,6]; the problems of perforating hydraulic fracturing in oil and shale gas extraction [7,8,9]; the stability of surrounding rock of tunnels in hydraulic and geotechnical fields [10,11,12]. It is formed by pouring epoxy resin into a metal or mica sheet that is prepositioned in a mold (regarded to be an internal crack) This method solves the problem of sample integrity of the cutting and pasting method and has been regarded as a mainstream research method for three-dimensional internal crack by scholars all over the world. 3D-ILC technology proposed by the author [35] was used to generate the 3D internal cracks in a brittle solid without any heterogeneous support materials and, at the same time, did not have any impact on the surface of the brittle solid; The transparent brittle material glass was selected to solve the problems of observing the process of crack propagation. Due to the penetration of electromagnetic field, the internal crack can be made without any influence on the surface by controlling the parameters
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