• 한국해양공학회지
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• 제30권6호
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• pp.474-483
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• 2016

Accidental events such as collisions, groundings, and hydrocarbon explosions in marine structures can cause catastrophic damage. Thus, it is extremely important to predict the extent of such damage, which determines the total amount of oil spills and the residual hull girder strength. Punching fracture tests were conducted by Choung (2009b), where various sizes of indenters and circular unstiffened steel plates with different thicknesses were used to quasi-statically realize damage extents. A three-dimensional fracture strain surface was developed based on a reference (Choung et al., 2015b), where the average stress triaxiality and average normalized Lode angle were used as the parameters governing the fracture of ductile steels. In this study, new numerical analyses were performed using very fine axisymmetric elements in combination with an Abaqus user-subroutine to implement the three-dimensional fracture strain surface. Conventional numerical analyses were also conducted for the tests to identify the best fit fracture strain values by changing the fracture strains. Based on the phenomenon of the average normalized Lode angle starting out positive and then becoming slightly negative, it was inferred that the shear stress primarily dominates in determining the fractures locations, with a partial contribution from the compressive stress. It should be stated that the three-dimensional fracture surface effectively predicted at least the shear stress-dominant fracture behavior of a mild steel.

• 동력기계공학회지
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• 제7권2호
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• pp.66-72
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• 2003

Recently, the steel parts used at the aerospace and automobile industries are required to be used light weight parts. Therefore, used material, steel have to be a high stress, which is an indispensable condition in this field. At the consideration of parts design, high hardness of the lightweight parts have an benefit of saving fuel and material. A high stress of metal has a point of difference according to the shape of design, external cyclic load and condition of vibration. A crack generates on the surface of metal or under yield stress by defect of inner metal defect or surface defect and slowly, this crack grow stable growth. Finally, rapidity failure phenomena is happen. Fatigue failure_phenomena, which happen in metal, bring on danger in human life and property therefor, anti-fatigue failure technology take an important part of current industries Currently, the shot peening is used for removing the defect from the surface of steel and improving the fatigue strength on surface. Therefore, this paper investigated the effect on frcature toughness using shot peening which is improve the resistance of crack growth and crack expansion rate by fatigue that make a compressive residual stress on surface.

• Geomechanics and Engineering
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• 제22권5호
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• pp.461-473
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• 2020

Natural rock mass contains defects of different shapes, usually filled with inclusions such as clay or gravel. The presence of inclusions affects the failure characteristics and mechanical properties of rock mass. In this study, the strength and failure characteristics of rock with inclusions were studied using the particle flow code under uniaxial compression. The results show that the presence of inclusions not only improves the mechanical properties of rock with defects but also increases the bearing capacity of rock. Circular inclusion has the most obvious effect on improving model strength. The inclusions affect the stress distribution, development of initial crack, change in crack propagation characteristics, and failure mode of rock. In defect models, concentration area of the maximum tensile stress is generated at the top and bottom of defect, and the maximum compressive stress is distributed on the left and right sides of defect. In filled models, the tensile stress and compressive stress are uniformly distributed. Failing mode of defect models is mainly tensile failure, while that of filled models is mainly shear failure.

• 한국재료학회지
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• 제15권11호
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• pp.697-704
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• 2005

The deformation behavior of a bulk amorphous and crystallized amorphous $Zr_{22.5}Ti_{14}Cu_{12.5}Ni_{10}Be_{22.5}$ alloy extracted from a commercial golf club head was characterized at room temperature ana $300^{\circ}C$. At room temperature, amorphous specimens revealed higher yield stress and ductility than partially crystallized alloy specimens. Amorphous alloy displayed some plasticity before fracture, which resulted from strain hardening and repeated crack initiation and propagation. The fracture is mainly localized on one major shear band, and the compressive fracture angle of the amorphous specimen between the stress axis and the fracture plane was about $40^{\circ}$ Scanning electron microscope observations revealed mainly a vein-like structure in the amorphous alloy But the fracture surface of partially crystallized amorphous alloy consisted of vein-like and featureless fracture structure. The partially crystallized alloy extracted from the thick part of the club fractured in the elastic region, at a much lower stress level than the amorphous, suggesting that relatively coarse crystal particles formed during cooling cause the brittle fracture.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2004년도 학술대회지
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• pp.239-241
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• 2004

Stress intensity factor of semi-circular crack front was calculated by FEM, and also allowable crack size which doesn‘t break out the fracture by SCC in residual stress field of STS materials. Allowable crack size was increased with compressive residual stress provided by shot peening on material surface, and with magnitude of compressive residual stress for depth direction.

• 한국정밀공학회지
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• 제8권1호
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• pp.41-49
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• 1991

A knowledge of the resdual stress distribution at circumferential weldments can normally increase the accuracy of a fracture assessment in pipe line. In this paper, we present the measurements about the residual stress distributions at three kinds of circumferential butt welded pipes using the holl drilling strain gage method. By this experiment, we have obtined the following characteristics. At the inner surface of the pipe region near the center line of welding is under high tensile residual stress. However, as the distance from the center line of welding increases, the tensile component decreases and finally becomes compressive residual stress at region far away from the center line of welding. The longitudinal residual stress at the outer surface is compressive regardless of the diameter of pipe and the circumferential stress is changed from compressive to tensile as pipe diameter increases. The results also demonstrate that the residual stress is mainly caused by self-restraint bending force in the pipe welding.

• 구강회복응용과학지
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• 제18권3호
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• pp.205-215
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• 2002

This study investigated the compressive fracture strength of Targis ceromer crown by the difference of occlusal thickness on a maxillary first premolar. Control group was a castable IPS-Empress all-ceramic crown with occlusal thickness of 1.5 mm constructed by layered technique. Experimental groups were Targis crowns having different occlusal thicknesses of 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, respectively. The classification of Targis group is T10, T15, T20, T25 and T15N (for no-thermocycling and occlusal thickness of 1.5mm). Ten samples were tested per each group. Except occlusal thickness, all dimension of metal die is same with axial inclination of $10^{\circ}$and marginal width 0.8mm chamfer. All crowns were cemented with Panavia F and thermocycled 1,000 times between $5^{\circ}$ and $55^{\circ}$ water bath with 10 sec dwelling time and 10 sec resting time. The compressive fracture strength was measured by universal testing machine. The results were as follows : 1. Fracture strength was increased as the occlusal thickness increased : compressive fracture strength of Group T10, T15, T20, T25 was $66.65{\pm}4.88kgf$, $75.04{\pm}3.01kgf$, $87.07{\pm}7.06kgf$ and $105.03{\pm}10.56kgf$, respectively. 2. When comparing material, Targis crown had higher fracture strength than IPS-Empress crown : the mean compressive strength of group T15 was $75.04{\pm}3.01kgf$ and the value of group Control was $37.66{\pm}4.28kgf$. 3. Fracture strength was decreased by thermocycling : the compressive fracture strength of T15 was $75.04{\pm}3.01kgf$, which is lower than $90.69{\pm}6.88kgf$ of group T15N. 4. The fracture line of crowns began at the loading point and extended along long axis of tooth. IPS-Empress showed adhesive failure pattern whereas Targis had adhesive and cohesive failure. In the SEM view, stress was distributed radially from loading point and the crack line was more prominent on Targis crown.

• 한국건설순환자원학회논문집
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• 제8권4호
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• pp.458-466
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• 2020

이 연구의 목적은 비정질 강섬유와 폴리아미드 섬유를 이용한 고성능 하이브리드 섬유보강 콘크리트의 압축 및 인장 거동을 평가하는 것이다. 이를 위하여 목표 압축강도 40MPa 및 60MPa 각각에 대해서 비정질 강섬유와 폴리아미드 섬유를 총 부피비로 1.0% 혼입한 고성능 하이브리드 섬유보강 콘크리트를 제작한 후 압축강도, 압축인성, 직접인장강도 및 응력-변형률 특징 등의 압축 및 인장 거동을 평가하였다. 그 결과, 고성능 하이브리드 섬유보강 콘크리트의 압축강도는 플레인 콘크리크보다 다소 감소하였으나, 압축인성, 압축인성 비, 직접인장강도는 크게 증가하는 것으로 나타났다. 또한 압축 및 인장 시험시 플레인 콘크리트는 최대응력 이후 취성파괴를 나타냈으나, HPHFRC는 변형연화 현상을 나타내어, 압축 및 인장 거동이 크게 개선되는 것으로 나타났다.

• 한국세라믹학회지
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• 제51권5호
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• pp.487-491
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• 2014

In this study, we measured the thermally and chemically induced residual stresses on glaze using the photoelastic method. Porcelain with thermally induced residual stress showed compressive stress of 49 MPa for thermal expansion mismatch and a locally fluctuated stress field over the glaze layer due to compensation of compressive stresses around pores. In the case of chemically strengthened porcelain, the compressive stress on the glaze was 151 MPa which was around 3 times higher than the stress on thermally strengthened glaze. The trend of fracture strength of thermally and chemically strengthened porcelains was coincident with that of the residual stress of porcelains.

• 한국정밀공학회지
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• 제23권9호
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• pp.127-133
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• 2006

Cold expansion method is used to protect a fatigue fracture from fastener hole in the structure and aerospace industry. Cold expansion is that an oversized tapered mandrel goes through the hole and produces a compressive residual stress as well as plastic deformation around the hole. Here, mandrel shapes are one of the factors which are influenced on the residual stress distribution by cold expansion method. This paper, according to mandrel shapes (diameter of mandrel, length of mandrel and length of taper), we are performed a finite element analysis of residual stress distribution by cold expansion method. From this study, it has been found that diameter of mandrel and length of taper are an important factor which was generated a low compressive residual stress surround of fastener hole by cold expansion method.