• Journal of Advanced Marine Engineering and Technology
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• 제29권8호
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• pp.855-861
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• 2005

Fracture toughness defined near the initiation of stable crack growth is investigated by R-curve and Direct Current electric Potential Determination(DCPD) under mode I plane strain conditions for CT specimen with 25.4mm thickness of SS400 steel. Fracture toughness. $J_{IC}$lit near crack tip of CT specimen by R-curve is 17.14 $kg_{f}/mm$ and however. its value by DCPD is 22.82 $Rg_{f} mm$ The value of fracture toughness by DCPD is larger than that by R-curve. Therefore, it is suggested that the evaluation of fracture toughness by R-curve is optimum than by DCPD, when considering amount of crack growth about each of fracture toughness.

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2001년도 추계학술발표회
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• pp.231-234
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• 2001

When constructing subsurface structures and/or wells, the precise estimates of hydraulic parameters must be obtained for operating safety and/or for developing necessary quantity of groundwater. Hydraulic conductivity is mainly subjected to the characteristics of fracture network in the fractured media such as fracture orientation and angle, fracture aperture and frequency, fracture length, interconnectivity of fractures, and filling material, feature of fracture plane. In this study we conducted water injection test at afferent depths on six boreholes drilled in granite of Mt. Geumjeong. hydraulic conductivity was calculated using Moye and Hvorslev methods. The relation between hydraulic conductivity and fracture frequency data obtained from acoustic televiewer and core log were analyzed. The result shows that the correlation between the hydraulic conductivity and the fracture frequency data obtained from acoustic televiewer is better than that with the core log.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.812-815
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• 2002

The shape of K-R curve for an ideally brittle material is flat because the surface energy is an unvaried material property. However, the K-R curve can take on a variety of shapes when nonlinear material behavior accompanies fracture. By the way, a general metallic material is nonlinear, structural steel is such. Therefore, the J-R curve form J-integral value instead of K parameters can be used to evaluate elastic-plastic materials with flaws in terms of ductile fracture that can be significant to design. In this paper, R-curve behaviors form K and J parameter is considered for the precise assessment of fracture analysis, in case of JS-SS400 steels.

• 한국도로학회논문집
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• 제8권1호
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• pp.139-152
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• 2006

Many experimental and numerical approaches have been developed to evaluate paving materials and to predict pavement response and distress. Micromechanical simulation modeling is a technology that can reduce the number of physical tests required in material formulation and design and that can provide more details, e.g., the internal stress and strain state, and energy evolution and dissipation in simulated specimens with realistic microstructural features. A clustered distinct element modeling (DEM) approach was implemented In the two-dimensional particle flow software package (PFC-2D) to study the complex behavior observed in asphalt mixture fracturing. The relationship between continuous and discontinuous material properties was defined based on the potential energy approach. The theoretical relationship was validated with the uniform axial compression and cantilever beam model using two-dimensional plane strain and plane stress models. A bilinear cohesive displacement-softening model was implemented as an intrinsic interface and applied for both homogeneous and heterogeneous fracture modeling in order to simulate behavior in the fracture process zone and to simulate crack propagation. A disk-shaped compact tension test (DC(T)) with heterogeneous microstructure was simulated and compared with the experimental fracture test results to study Mode I fracture. The realistic arbitrary crack propagation including crack deflection, microcracking, crack face sliding, crack branching, and crack tip blunting could be represented in the fracture models. This micromechanical modeling approach represents the early developmental stages towards a 'virtual asphalt laboratory,' where simulations of laboratory tests and eventually field response and distress predictions can be made to enhance our understanding of pavement distress mechanisms, such its thermal fracture, reflective cracking, and fatigue crack growth.

• 한국압력기기공학회 논문집
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• 제11권1호
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• pp.69-73
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• 2015

The study investigated effects of residual stresses and Charpy impact energy on brittle fractures of the butt weld between the valve and the piping, and of the valve body in nuclear power plants via a linear elastic fracture mechanics approach in the ASME B&PV Code, Sec.XI and finite element analysis. Weld residual stress in a butt weld between close check valve and piping, and residual stress in the valve due to casting process were assumed to be proportional to yield strength of base metal. Operating stresses in the butt weld and the valve body were calculated using approximate engineering formulae and finite element analysis, respectively. Applied stress intensity factors were calculated by assuming postulated cracks with specific sizes and then by substituting the residual stresses and the operating stresses into engineering formulae presented in the ASME B&PV Code, Sec.III. Plane strain fracture toughness was derived by using a correlation between Charpy V-notch impact energy and fracture toughness. Structural integrity of the weld and the body against brittle fracture was assessed by using the applied stress intensity factors, plane strain fracture toughness and the linear elastic fracture mechanics approach. As a result, it was identified that the structural integrity was maintained with decreasing the residual stress levels and increasing the Charpy V-notch impact energy.

• 대한기계학회논문집A
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• 제27권9호
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• pp.1531-1538
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• 2003

This paper compiles solutions of plastic $\eta$ factors and crack tip stress triaxialites for standard and nonstandard fracture toughness testing specimens, via detailed three-dimensional (3-D) finite element (FE) analyses. Fracture toughness testing specimens include a middle cracked tension (M(T)) specimen, SE(B), single-edge cracked bar in tension (SE(T)) and C(T) specimen. The ligament-to-thickness ratio of the specimen is systematically varied. It is found that the use of the CMOD overall provides more robust experimental J estimation than that of the LLD, for all cases considered in the present work. Moreover, the J estimation based on the load-CMOD record is shown to be insensitive to the specimen thickness, and thus can be used for testing specimen with any thickness. The effects of in-plane and out-of-plane constraint on the crack tip stress triaxiality are also quantified, so that when experimental J value is estimated according to the procedure recommended in this paper, the corresponding crack tip stress triaxiality can be estimated. Moreover, it is found that the out-of-plane constraint effect is related to the in-plane constraint effect.

• 한국주조공학회지
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• 제10권5호
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• pp.408-416
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• 1990

The application of this new design approach called fracture mechanics allow one to determine the maximum allowable stress from the knowledge of the largest expected flow size and the plane strain fracture toughness of a material. In this study we examined the relation between retained austenite, mechanical property and fracture toughness accompanied by austempering heat treatment. Fracture toughness values and retained austenite volume were higher with the ADI(austempered ductile iron) which were austempered at $380^{\circ}C$ than austempered at $320^{\circ}C$. Additionally, fracture toughness values were increased for 1~2 hour austempering time but it was slowly decreased for 5 hour ADI maintaining the predominant fracture toughness($K_{IC}:83MPa{\sqrt{m}}$) is obtained following condition, namely, austempering temperature and time ($380^{\circ}C$ and 1 hour).

• Tribology and Lubricants
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• 제15권2호
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• pp.141-149
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• 1999

Fracture, fatigue and wear characteristics of Al-Si alloy used for compressor are experimentally studied. Plane strain fracture toughness test is carried out using three point bending specimen. Fatigue test is performed under constant loading condition and wear test is carried out as a function of sliding velocity and applied load. To obtain the crack propagation characteristics and wear mechanism of Al-Si alloy, fracture and worn surfaces are investigated using SEM. It is verified that fracture and fatigue strength of Al-Si alloy are improved by the fine microstructure of alloy. The wear behavior and specific wear amount of Al-Si alloy are not dependent on the microstructure but on a function of the silicon content. Anodizing on the surface of Al-Si alloy, surface hardness and wear characteristics are improved.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2000년도 추계학술발표대회 논문집
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• pp.110-114
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• 2000

The Interlaminar fracture behavior of hybrid composite with non-woven carbon tissue was investigated under Mode I (DCB) and Mode II (ENF) loading condition. Hybrid composites were manufactured by means of inserting a non-woven tissue between prepreg layers. Two kinds of specimens were prepared from [0]$_{24}$ and [$0_{12}/0_{12}$]. Where, the symbol "/" means that a non-woven carbon tissue was located at 0/0 mid-plane of the specimen. The interlaminar fracture toughness of hybrid composites was compared with that of CFRP. The fracture surfaces of the specimens were observed using optical microscope and SEM, and the failure mechanism was discussed. The hybrid laminates, which are made by inserting non-woven carbon tissue between layers, were shown to be effective to remarkably improve Mode II fracture toughness.toughness.

• 한국해양공학회지
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• 제34권3호
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• pp.155-166
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• 2020

Ductile fracture prediction is critical for the reasonable damage extent assessment of ships and offshore structures subjected to accidental loads, such as ship collisions and groundings. A fracture model combining the Hosford-Coulomb ductile fracture model with the domain of solid-to-shell equivalence model (HC-SDDE), was used in fracture simulations based on shell elements for the punching fracture experiments of unstiffened and stiffened panels. The flow stress and ductile fracture characteristics of JIS G3131 SPHC steel were identified through tension tests for flat bar, notched tension bar, central hole tension bar, plane strain tension bar, and pure shear bar specimens. Punching fracture tests for unstiffened and stiffened panels are conducted to validate the presented HC-DSSE model. The calibrated fracture model is implemented in a user-defined material subroutine. The force-indentation curves and final damage extents obtained from the simulations are compared with experimental results. The HC-DSSE fracture model provides reasonable estimations in terms of force-indentation paths and residual damage extents.