• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.12
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• pp.2004-2010
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• 2003

Fracture life and crack retardation behavior were examined experimentally using CT specimens of aluminum alloy 5083. Crack retardation life and fracture life were a wide difference. between 0.8 and 0.6 in proportion to ratio of load reduction. The wheeler model retardation parameter was used successfully to predict crack growth behavior. By using a crack propagation rule, prediction of fracture life can be evaluated quantitatively. A statistical approach based on Weibull distribution was applied to the test data to evaluate the dispersion in the retardation life and fracture life by the change of load reduction.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.12
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• pp.198-204
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• 2003

The bone fracture healing is simulated by using one of the complex system rules, named cellular automata method. It is assumed that each cell has property of Bone, Cartilage or Fibrous connective tissue. Nine local rules are adopted to change the property of each cell against the mechanical stimulus, which consists of the strain energy density, and the existence of bone in the surroundings. Two dimensional sheep metatarsal model is considered and the bone fracture healing is simulated. The simulation results agree well with those obtained by using fuzzy logic model and experimental data. The cellular automata method found to be one of the simulation methods to express the bone fracture healing. The cellular automata method is expected to be effective in representing biological phenomenon.

• Explosives and Blasting
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• v.23 no.2
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• pp.45-56
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• 2005

In this study, fracture formation and fracture volume by blasting demolition of model reinforced concrete pillars were compared with various vertical load and influence of reinforced steel bar. The more vertical load increased, the more tensile cracks and vertical direction cracks produced. In vertical load of 2.0ton, tensile cracks on vertical direction were predominantly produced. Generally, the more vertical load increased, the more bending deformation of concrete steel bar decreased. As a result, vertical load was influenced fracture formation of concrete and bending deformation of reinforced steel bar. Reinforced steel bar was influenced fracture volume of concrete. According to vertical load and influence of reinforce steel bar by blasting demolition of reinforced concrete pillars, drilling and blasting pattern may be modified.

• Journal of the Korean Society of Groundwater Environment
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• v.5 no.2
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• pp.80-87
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• 1998

Since groundwater flow paths have one of the major roles to transport the radioactive nuclides from the radioactive waste repository to the biosphere, the discrete fracture network model is used for the rock block scale flow instead of the porous continuum model. This study aims to construct a three dimensional discrete fracture network to interpret the groundwater flow system in the study site. The modeling work includes the determination of the probabilistic distribution function from the fracture geometric and hydraulic parameters, three dimensional fracture modeling and model calibration. The results of the constant pressure tests performed in a fixed interval length at boreholes indicate that the flow dimension around boreholes shows mainly radial to spherical flow pattern. The fracture transmissivity value calculated by Cubic law is 6.12${\times}$10$\^$-7/ ㎡/sec with lognormal distribution. The conductive fracture intensity estimated by FracMan code is 1.73. Based on this intensity, the total number of conductive fractures are obtained as 3,080 in the rock block of 100 m${\times}$100 m${\times}$100 m.

• Geomechanics and Engineering
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• v.9 no.5
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• pp.645-667
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• 2015

Single treatment and staged treatments in vertical wells are widely applied in sandstone and mudstone thin interbedded (SMTI) reservoir to stimulate the reservoir. The keys and difficulties of stimulating this category of formations are to avoid hydraulic fracture propagating through the interface between shale and sand as well as control the fracture height. In this paper, the cohesive zone method was utilized to build the 3-dimensional fracture dynamic propagation model in shale and sand interbedded formation based on the cohesive damage element. Staged treatments and single treatment were simulated by single fracture propagation model and double fractures propagation model respectively. Study on the changes of fracture vicinity stress field during propagation is to compare and analyze the parameters which influence the interfacial induced stresses between two different fracturing methods. As a result, we can prejudge how difficult it is that the fracture propagates along its height direction. The induced stress increases as the pumping rate increasing and it changes as a parabolic function of the fluid viscosity. The optimized pump rate is $4.8m^3/min$ and fluid viscosity is $0.1Pa{\cdot}s$ to avoid the over extending of hydraulic fracture in height direction. The simulation outcomes were applied in the field to optimize the treatment parameters and the staged treatments was suggested to get a better production than single treatment.

• Computers and Concrete
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• v.24 no.6
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• pp.527-539
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• 2019

In this paper, the fracture characteristics of concrete specimens with different notch depths under three-point flexural loads are studied by finite element and fracture mechanics methods. Firstly, the concrete beams (the size is 700×100×150 mm) with different notch depths (a=30 mm, 45 mm, 60 mm and 75 mm respectively) are tested to study the influence of notch depths on the mechanical properties of concrete. Subsequently, the concrete beams with notch depth of 60 mm are loaded at different loading rates to study the influence of loading rates on the fracture characteristics, and digital image correlation (DIC) is used to monitor the strain nephogram at different loading rates. The test results show that the flexural characteristics of the beams are influenced by notch depths, and the bearing capacity and ductility of the concrete decrease with the increase of notch depths. Moreover, the peak load of concrete beam gradually increases with the increase of loading rate. Then, the fracture energy of the beams is accurately calculated by tail-modeling method and the bilinear softening constitutive model of fracture behavior is determined by using the modified fracture energy. Finally, the bilinear softening constitutive function is embedded into the finite element (FE) model for numerical simulation. Through the comparison of the test results and finite element analysis, the bilinear softening model determined by the tail-modeling method can be used to predict the fracture behavior of concrete beams under different notch depths and loading rates.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2006.06a
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• pp.43-44
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• 2006

Generally almost all fatigue crack growth is affected by model. For this reason a study on model has concentrated in the field of fracture mechanics. However the fatigue crack initiation and growth in machines and structures usually occur in mixed mode loading. If there is any relationship between the cause of fracture in mixed mode loading and fracture surface, fracture surface pattern will be the main mean explaining reasons of fatigue fracture and obtaining further information about fracture process. In this paper four point shear-fatigue test with Aluminum alloy Al 5083-O is carried out from this prospect and then the mixed mode distribution of fracture surface is examined from the result after identifying the generation of fatigue crack surface pattern. It was found from the experimental results that the fatigue crack surface pattern and the fatigue crack shear direction are remarkably consistent. Furthermore It is possible that the analysis of distribution of mixed mode through the fatigue crack surface pattern.

• International Journal of Concrete Structures and Materials
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• v.18 no.3E
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• pp.191-198
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• 2006

The objective of this study is to examine fracture characteristics of concrete at early ages, i.g. critical stress intensity factor, critical crack-tip opening displacement, fracture energy, and bilinear softening curve based on the concepts of effective-elastic crack model and cohesive crack model. A wedge splitting test for Mode I was performed on cubic wedge specimens with a notch at the edge. By experimenting with various strengths and ages, load-crack mouth opening curves were obtained, and the results were analyzed by linear elastic fracture mechanics and FEM(finite element method). The results from the test and analysis showed that critical stress intensity factor and facture energy increased while critical crack-tip opening displacement decreased with concrete aging from 1 day to 28 days. Four parameters of bilinear softening curve from 1 day to 28 days were obtained from a numerical analysis. The obtained fracture parameters and bilinear softening curves at early ages from this study are to be used as a fracture criterion and an input data for the finite element analysis of concrete at early ages.

• Steel and Composite Structures
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• v.32 no.2
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• pp.199-212
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• 2019

This paper presents an investigation on seismic behavior of out-of-code Q690 circular high-strength concrete-filled thin-walled steel tubular (HCFTST) columns made up of high-strength (HS) steel tubes (yield strength $f_y{\geq}690MPa$). Eight Q690 circular HCFTST columns with various diameter-to-thickness (D/t) ratios, concrete cylinder compressive strengths ($f_c$) and axial compression ratios (n) were tested under the constant axial loading and reversed cyclic lateral loading. The obtained lateral load-displacement hysteretic curves, energy dissipation, skeleton curves and ductility, and stiffness degradation were analyzed in detail to reflect the influences of tested parameters. Subsequently, a simplified shear strength model was derived and validated by the test results. Finally, a finite element analysis (FEA) model incorporating a stress triaxiality dependent fracture criterion was established to simulate the seismic behavior. The systematic investigation indicates the following: compared to the D/t ratio and axial compression ratio, improving the concrete compressive strength (e.g., the HS thin-walled steel tube filled with HS concrete) had a slight influence on the ductility but an obvious enhancement of energy dissipation and peak load; the simplified shear strength model based on truss mechanism accurately predicted the shear-resisting capacity; and the established FEA model incorporating steel fracture criterion simulated well the seismic behavior (e.g., hysteretic curve, local buckling and fracture), which can be applied to the seismic analysis and design of Q690 circular HCFTST columns.

• Structural Engineering and Mechanics
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• v.36 no.3
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• pp.343-361
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• 2010

The Discrete Element Method adopting particles for the domain discretization has recently been adopted in fracture studies of non-homogeneous continuous media such as concrete and rock. A model is proposed in which the reinforcement is modelled by 1D rigid-spring discrete elements. The rigid bars interact with the rigid circular particles that simulate the concrete through contact interfaces. The DEM enhanced model with reinforcement capabilities is evaluated using three point bending and four point bending tests on reinforced concrete beams without stirrups. Under three point bending, the model is shown to reproduce the expected final crack pattern, the crack propagation and the load displacement diagram. Under four point bending, the model is shown to match the experimental ultimate load, the size effect and the crack propagation and localization.