Papers by Keyword: Crack Coalescence

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Authors: Yohei Sonobe, Takuichiro Ino, Akihide Saimoto, Md. Abdul Hasib, Atsuhiro Koyama, Giora Shatil
Abstract: In a standard body force method analysis, a mesh division is required to define the boundary of a problem and to solve a governing equation using discretization procedure. However, in the present study, a moving least square strategy is introduced to define a weight function for the density of body force doublet and therefore a crack analysis is carried out without providing a standard mesh-division. Hence, the standard crack face elements are not required at all. A variety of 3D crack problems can be analyzed simply by providing a data that only de nes a crack front. Besides the nodal points for crack front, several internal nodes are generated on the crack face to represent a distribution of unknown function. At the internal nodes, an unknown variable is assigned which uniquely de ne a distribution of the relative crack face displacement. In the present approach, a crack problem is formulated as a singular integral equation whose unknown is a value of the weight function at the internal nodal points. A crack growth can be simulated directly by changing the shape of crack front, by means of adding a new nodal point in the vicinity of the current crack front. In the present paper, the proposed method is used to simulate a coalescence of interacting planar cracks.
Authors: Jun Lian He, Ming Tian Li
Abstract: Crack coalescence, which was responsible for some engineering disasters such as rock burst, and so on, was studied by one new numerical method-lattice cellular automata. A cellular automaton is made up of cell, lattice, state, neighbor and rule. It has advantages of locality, parallelization etc. Lattice cellular automata are presented which have the advantages of both cellular automata and lattice model. In this model cell will be connected with its neighbor cells in virtue of beams. The basic thoughts of LCA can be expressed as below. The heterogeneity of rock is introduced by randomly assigning the mechanical parameters of beams following Weibull distribution. According to equilibrium equations, deform equations and the constitute equations the local rules of cells can be constructed. Then lattice cellular automata were used to study the coalescence of two cracks with different geometries. The influences of arrangement and spacing of two cracks on the coalescence were studied. The numerical simulation results were in good accordance with the experimental results.
Authors: Ri Hong Cao, Ping Cao, Hang Lin
Abstract: In practical engineering, the joints or fissures with similar characteristics are commonly found in natural rocks, they decrease the mechanics properties of the rock mass and also can be seen as a source of initiation of new discontinuities. The previous studies (experimental or numerical) has promoted the understanding of coalescence patterns or failure process obtained from brittle specimens which contain single, two or three fissures. However, the failure characteristics of multi-fissure specimens has not been studied comprehensively. In this paper, the crack coalescence pattern and failure mode of the rock-like materials with multi-fissures have been explored. Based on the experiment results, under unaxial compression, we found that the coalescence modes between fissures can be generally classified into three categories: T/S/M pattern. Moreover, due to the difference of inclination angle and fissure numbers, the specimens present different failure mode. Careful examination all of specimens, the failure mode can be classified into 4 categories: Mix failure model(shear+splitting), Shear failure, Stepped path, Intact failure.
Authors: Shan Lin Liu, Lu Wang, Zheng Wang
Abstract: The fatigue behavior of 2A12 Aluminum alloy was experimentally studied through different annular notched specimens under symmetrical triangle with the frequency of 0.5 Hz. The experimental result showed that the microstructure played an important role during the entire fatigue life of 2A12 Aluminum alloy. The short fatigue crack only initiated due largely to the second-phase particle such as the S phase (Al2CuMg), the θ phase (CuAl2) and especially the black impurity phases debonding from the basal body when the fatigue cycle was sufficient. The cracks propagated separately along the circumferential direction of the notch, crack coalescence and interaction of cracks were not common at early and middle stage of short crack’s fatigue life. Cracks tended to propagate along direction different from the original one after crack coalescence. Surface crack length at early and middle stage of short crack’s fatigue life were presented. These curves showed crack growth rate increased relatively as the reducing of notched radius or the increasing of nominal strain amplitude which implied that geometry and loading conditions were the factors of the crack propagation.
Authors: Keiichiro Tohgo, Nobuhiro Ogai
Abstract: According to laboratory accelerated test data, stress corrosion cracking (SCC) in structural metal materials occurs by initiation and coalescence of micro cracks, subcritical crack growth, multiple large crack formation and final failure under the combination of materials, stress and corrosive environment. In this paper, a computer simulation model for the process of SCC has been proposed. The procedure is as follows: The possible number of crack initiations is set for a given space and the initiation times for all cracks are assigned by random numbers based on exponential distribution. The sites and length of the cracks are assigned by uniform random numbers and normal random numbers, respectively. The coalescence of cracks and the subcritical crack growth are determined based on the fracture mechanics. The simulation is terminated when the maximum crack length reaches a critical value or all of the possible number of cracks is initiated. The results obtained in this paper indicate the applicability of the present model to predict the SCC behavior in real structures based on the laboratory accelerated test data.
Authors: Keiichiro Tohgo, Hiromitsu Suzuki, Yoshinobu Shimamura
Abstract: According to laboratory accelerated test data, stress corrosion cracking (SCC) in structural metal materials occurs by initiation and coalescence of micro cracks, subcritical crack propagation and multiple large crack formation or final failure under the combination of materials, stress and corrosive environment. In this paper, a Monte Carlo simulation for the process of SCC has been proposed based on the stochastic properties of micro crack initiation and fracture mechanics concept for crack coalescence and propagation. The emphasis in the model is put on the influence of the semi-elliptical surface cracks. The numerical examples for a sensitized stainless steel type 304 indicate the applicability of the present model to the prediction of the SCC behavior in real structures.
Authors: P. Lin, R.H.C. Wong, K.T. Chau, Chun An Tang
Authors: Yu Jun Zuo, Chun An Tang, Zheng Zhao Liang, Yong Bin Zhang
Abstract: Using newly developed 3 dimensional Rock Failure Process Analysis code RFPA3D, numerical simulations on samples of rock-like material containing pre-existing surface closed flaws under uniaxial compressive loading are conducted to investigate the failure mechanism and crack coalescence modes. Friction in closed flaws is modeled by inserting ideal elasto-plastic materials into the flaws. The simulations replicate most of the phenomena observed in actual experiments, such as initiation and growth of wing and secondary cracks, crack coalescence, and the macro-failure of the sample. For the samples containing three pre-existing surface closed flaws, four different patterns of crack coalescence are obtained in our simulations. The four different patterns of coalescence are the combination of T mode, S mode, TS mode and C mode, i.e. type (C+S mode), (T+S mode),  (S mode) and (C+S mode). A total of four types of samples containing three surface parallel inclined frictional flaws are numerically simulated.
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