Papers by Keyword: Crack Extension

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Authors: Li Yu, Ming Fu Fu, Bin Tu
Abstract: Firstly, in the paper based on the constitutive equation and the basic equations of the unloading fractured rock mass on the second expansion phase at the crack, the two types of variables of the energy functional about the variation problem was constructed the,as the independent variables at that stage. In order to identify the undetermined function G,the energy functional variational the independent variables ,,the variational function was satisfied the principle of minimum potential then can obtain the function G. Second, Secondly on this basis, two undetermined Lagrange multipliers were introduced to the new functional in order to absorb the balance equation and stress boundary conditions into the new functional .As the same, variational the independent variables,, then obtained the . To simplify the using the Green formula and then can be identified the undetermined Lagrange multipliers.Finally,the unloading the fractured rock mass at the crack of secondary expansion phase of the unconstrained variational energy functional can be obtained which is the generalized variational principle.
Authors: Yan Hua Zhao, Hua Zhang, Wei Dong
Abstract: The wedge splitting (WS) test is now a promising method to perform stable fracture mechanics tests on concrete-like quasi brittle materials. Fracture parameters, such as fracture toughness and critical crack opening displacement and, are however not easy to determined since formulae available from stress intensity factor manual are restricted to standard specimen geometry. The paper attempts to compute expressions for commonly used fracture parameters for a general wedge splitting specimen. By means of finite element analysis program, test simulation was performed on non-standard wedge splitting specimen with different depth and initiation crack length, and thereafter expressions were proposed for stress intensity factor at the pre-cast tip and crack mouth opening displacement on the load line. Based on the work above, size effect on the unstable fracture toughness and crack extension were investigated, and the consistency of fracture toughness data for various specimen depth as well as initiation crack length is demonstrated. The crack extension is little sensitive to the initiation crack length, it increases with the depth of specimen, which can be explained by the boundary influence of the specimen.
Authors: Byung Nam Kim, Y. Katsukawa, B.W. Ahn, Manabu Enoki, T. Kishi
Authors: Min Zheng Jiang, Yang Li, Yi Ming Zhang, Tian Xue Jiang, Ming Xing Liu
Abstract: Widespread problem in hydraulic fracturing of low-permeability reservoir is difficulty of crack initiation of fracturing, high initiation pressure of fracturing put forward higher requirements of fracturing equipment. Low-permeability reservoir for the study, in the fluid-solid coupling conditions, established a low-permeability reservoir perforation mechanical model of stress, using numerical solution techniques, consider the dynamic effects, we can achieve the stress distribution at different stages: drilling, well cementation, perforation and fracturing in low-permeability reservoir. With rock tensile fracture criterion can determine the initiation location and initiation pressure. The results show that the lower the degree of pollution in perforating hole, the smaller the pressure from the crack initiation as well as the higher the degree of pollution in perforating hole, the larger the pressure from the crack initiation. Orientation, diameter and depth of perforating hole effect on crack initiation and extension are more significant.
Authors: Luboš Náhlík, Zdeněk Knésl, F. Kroupa
Abstract: Plasma-sprayed ceramic coatings contain a high density of intrasplat microcracks which are responsible for small Young’s moduli and low fracture toughness. The extension of an initial surface crack in the direction to the interface, where the crack is repelled by the metal substrate with higher Young’s modulus, is studied using the methods of fracture mechanics. It is shown that high tensile stresses induced by the crack in the interface can lead to a local decohesion along the interface so that the crack can deviate into the interface.
Authors: Xiao Ying Liu, Xiao Xiang Yang, Xiu Rong Wang
Abstract: Presented herein is a finite element investigation into the damage mechanism of the adhesive interface of the rubber-steel bimaterial. The cohesive element layer is used at the interface to simulate the initial loading, initiation and propagation of the damage. From the simulation results, it is found that interface strength exert significant effects on the crack formation in the interface. Smaller interface strength could lead to crack initiation more easily.
Authors: Guo Sheng Lu, Xun Wang, Xiao Lan Chen
Abstract: Fractured rock mass endures tensile-shear and pressure-shear effects under horizontal seismic force. Based on rock fracture mechanics and the maximum circumferential stress theory, the extending condition (that is, the critical acceleration), the extending direction and the crack extension length under different direction of horizontal seismic force have been studied. The results are useful for judging the risk of dangerous rocks and providing a theoretical basis of pre-identification in the earthquake zone.
Authors: Xue Li Cheng, Chang Liu Tian
Abstract: In this paper, the ultrasonic vibration uniaxial tension experiment was carried out on the 20# steel with a set of ultra-high-frequency vibration device. It showed that the material defect was the important factors of ultrasonic “soften” mechanism and obtained the crack extension mechanism under ultrasonic fatigue loading, there were:(1)The high frequency vibration of the ultrasonic fatigue loading weakened the influence of the plastic zone of the crack tip and residual stress on crack extension; (2)When the fatigue crack extension, the ultrasonic wave spread in the specimen, and reflected in the crack surface, resulting the crack closure effect decreased, the plastic zone of the crack tip decreasing; (3)The high vibration frequency and deformation velocity resulted the increase of the thermal effect, crack extension energy spread to the continuous medium in the form of heat, promoting crack extension and releasing energy. It also study the influence of different groove depth and groove curvature on the material ultrasound fatigue limit, and obtained the relation curve of fatigue limit with groove depth and groove curvature.
Authors: Bing Jun Si, Qiao Jin
Abstract: Aimed at deep-sea steel catenary risers(SCRs) transporting supercritical or dense CO2, this paper uses the macroscopic pipeline-transporting finite element model and the microscopic pipewall crack growth model to numerically simulate corrosive-inwall-defect-induced crack extension along radial direction for the deep-sea riser which is subjected to wave and current loads. Meanwhile, based on linear elastic fracture mechanics and fatigue crack extension theory, the effect of wave height on the fatigue life of the pipewall at touchdown zone is discussed. The above-mentioned study in this paper is expected to give a good reference to the similar study for oil&gas SCRs.
Authors: Mitsuo Notomi, Kikuo Kishimoto, Tie Jun Wang, Toshikazu Shibuya
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