• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2000년도 제32회 추계학술대회 정기총회
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• pp.50-58
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• 2000

A linear elastic fracture mechanics analysis of multiful subsurface cracks propagation in a half-space subjected to moving thermomechanical surface traction was peformed using the finite element method. The effect of frictional heat at the sliding surface on the crack growth behavior is analyzed in terms of the thermal load and peclet number. The crack propagation direction is predicted in light of the magnitudes of the maximum shear and tensile stress intensity factor ranges. When moving thermomechanical surface traction exists, subsurface horizontal cracks are propagation in-plane crack growth rate at the beginning but they are propagation out-of-plane crack growth rate by the frictional heat which is occurrence by the repeated sliding contact.

• Geomechanics and Engineering
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• 제14권3호
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• pp.225-231
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• 2018

In this paper, in order to explain the splitting of cylindrical rock specimen under uniaxial loading, cracks in cylindrical rock specimen are divided into two kinds, the longitudinal crack and the slanting crack. Mechanical behavior of the rock is described by elastic-brittle-plastic model and splitting is assumed to suddenly occur when the uniaxial compressive strength is reached. Expression of the stresses induced by the longitudinal crack in direction perpendicular to the major axis of the crack is deduced by using the Maxwell model. Results show that the induced stress is tensile and can be greater than the tensile strength even before the uniaxial compressive strength is reached. By using the Inglis's formula and simplifying the cracks as slender ellipse, the above conclusions that drawn by using the Maxwell model are confirmed. Compared to shearing fracture, energy consumption of splitting seems to be less, and splitting is most likely to occur when the uniaxial loading is great and quick. Besides, explaining the rock core disking occurred under the fast axial unloading by using the Maxwell model may be helpful for understanding that rock core disking is fundamentally a tensile failure phenomenon.

• 대한금속재료학회지
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• 제49권1호
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• pp.1-8
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• 2011

To measure the sensitivity of the hydrogen embrittlement from plated high strength bolts (SWCH18A, F11T), the bolt was stressed by a corresponding to the amount of tensile strain of 5% and 20%, and then the bolt developed a crack on the surface. The bolt that didn't have concentrated hydrogen, even though it was stressed by a corresponding the amount of tensile strain of 5% and 20%, no crack developed. However, the bolt that had concentrated hydrogen, developed cracks from the thread crest to the root. It is impossible to measure the hydrogen amount from plated high strength bolts using Hydrogen-Determinator, because of the limitation of the minimum sample size (about 1g as a mass or $5{\times}5{\times}5 mm^3$ as a volume). Therefore, the sensitivity of hydrogen embrittlement can be measured by observing the presence of cracks on the surface of plated high strength bolts which are stressed by a corresponding to the amount of tensile strain of 5% and 20%.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 추계학술대회 논문집
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• pp.1000-1004
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• 2007

Thermal cracks are among the key factors that control the quality of a brake disk. Thermal cracks may shorten the lifetime of the disc and increase brake noise. Therefore, high heat-resistant brake disk materials are needed. In this study, three kinds of disk material were tested. They are composed of C, Si, Mn, P, S, Cu, Cr, Mo, and Ni. For the three materials, tensile tests, hardness measurement, metallurgical structure analysis, image analyzer analysis, etc were carried out. And friction tests were performed by a small scale dynamometer.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 가을 학술발표대회 논문집(III)
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• pp.633-636
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• 1998

The use of concrete pavements is increasing by virtue of durability and excellent load resisting capacity. But cracks and demage in concrete pavements may be occurred by continuous reciclic load, as time goes by. Therefore, transverser contraction joints are constructed in concrete pavements to relieve tensile stresses, and when properly spaced they control the location of transverse cracks.

• Design & Manufacturing
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• 제12권1호
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• pp.13-17
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• 2018

It was analyzed and experimented on the change of the material thickness according to the size of the "R" of the punch and die corners using the material of SCP-1 0.25mm As a result, the following conclusions were obtained. Tensile strength analysis and safety analysis of materials are very important process for each process in strip layout, and Through this, the Influx of material and the deformation of the material were found. As a result of safety analysis and tensile thickness analysis, when the corner R of the punch was 0.3 mm and the edge R of the die was 1.0 mm The inflow of the material was not smooth, and the thickness of the corner part became 0.2 mm, causing cracks. when the corner R of the punch was 0.5 mm and the edge R of the die was 1.5 mm The inflow of the material was smooth, The thickness of the corners of the product is 0.21mm and It was considered that cracks do not occur when the thickness of the bottom surface and the body part becomes thin. The results obtained by applying the results obtained from the analysis, In Experimental Condition 1, a crack occurred in the same part of the analysis In Experimental Condition 2, the flow of the material was smooth and the drawing processing could be performed without generating cracks.

• Advances in concrete construction
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• 제14권5호
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• pp.317-330
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• 2022

This paper investigated computationally and experimentally the interaction here between a notch as well as a micropore under uniaxial compression. Brazilian tensile strength, uniaxial tensile strength, as well as biaxial tensile strength are used to calibrate PFC2d at first. Then, uniaxial compression test was conducted which they included internal notch and micro pore. Experimental and numerical building of 9 models including notch and micro pore were conducted. Model dimensions of models are 10 cm × 10 cm × 5 cm. Joint length was 2 cm. Joints angles were 30°, 45° and 60°. The position of micro pore for all joint angles was 2cm upper than top of the joint, 2 cm upper than middle of joint and 2 cm upper than the joint lower tip, discreetly. The numerical model's dimensions were 5.4 cm × 10.8 cm. The fractures were 2 cm in length and had angularities of 30, 45, and 60 degrees. The pore had a diameter of 1 cm and was located at the top of the notch, 2 cm above the top, 2 cm above the middle, and 2 cm above the bottom tip of the joint. The uniaxial compression strength of the model material was 10 MPa. The local damping ratio was 0.7. At 0.016 mm per second, it loaded. The results show that failure pattern affects uniaxial compressive strength whereas notch orientation and pore condition impact failure pattern. From the notch tips, a two-wing fracture spreads almost parallel to the usual load until it unites with the sample edge. Additionally, two wing fractures start at the hole. Both of these cracks join the sample edge and one of them joins the notch. The number of wing cracks increased as the joint angle rose. There aren't many AE effects in the early phases of loading, but they quickly build up until the applied stress reaches its maximum. Each stress decrease was also followed by several AE effects. By raising the joint angularities from 30° to 60°, uniaxial strength was reduced. The failure strengths in both the numerical simulation and the actual test are quite similar.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2016년도 추계 학술논문 발표대회
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• pp.7-8
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• 2016

The use of half PC slab is increasing to shorten construction period. Because the drying shrinkage of topping concrete is restrained by PC slab, the tensile stress is generated at the topping concrete and the cracks can be occurred at the topping concrete due to drying shrinkage. Therefore, it is important to predict the tensile strain of half PC slab due to drying shrinkage to improve the quality of half PC slab. However, there is no studies on prediction of shrinkage behavior of half PC slab yet. Therefore, in this study, half PC slab was made, and the predictability of tensile strain generated at half PC slab due to drying shrinkage was investigated. The step by step method considering creep was used to estimate the tensile strain of half PC slab. In result, good agreement was obtained between the analytical and experimental values.

• Steel and Composite Structures
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• 제46권1호
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• pp.53-73
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• 2023

Man-made structure materials like concrete usually contain inclusions. These inclusions affect the mechanical properties of concrete. In this investigation, the influence of inclusion length and inclination angle on three-dimensional failure mechanism of concrete under uniaxial compression were performed using experimental test and numerical simulation. Approach of acoustic emission were jointly used to analyze the damage and fracture process. Besides, by combining the stress-strain behavior, quantitative determination of the thresholds of crack stress were done. concrete specimens with dimensions of 120 mm × 150 mm × 100 mm were provided. One and two holes filled by gypsum are incorporated in concrete samples. To build the inclusion, firstly cylinder steel tube was pre-inserting into the concrete and removing them after the initial hardening of the specimen. Secondly, the gypsum was poured into the holes. Tensile strengths of concrete and gypsum were 2.45 MPa and 1.5 MPa, respectively. The angle bertween inclusions and axial loadind ary from 0 to 90 with increases of 30. The length of inclusion vary from 25 mm to 100 mm with increases of 25 mm. Diameter of the hole was 20 mm. Entirely 20 various models were examined under uniaxial test. Simultaneous with experimental tests, numerical simulation (Particle flow code in two dimension) were carried out on the numerical models containing the inclusions. The numerical model were calibrated firstly by experimental outputs and then failure behavior of models containing inclusions have been investigated. The angle bertween inclusions and axial loadind vary from 0 to 90 with increases of 15. The length of inclusion vary from 25 mm to 100 mm with increases of 25 mm. Entirely 32 various models were examined under uniaxial test. Loading rate was 0.05 mm/sec. The results indicated that when inclusion has occupied 100% of sample thickness, two tensile cracks originated from boundaries of sample and spread parallel to the loading direction until being integrated together. When inclusion has occupied 75% of sample thickness, four tensile cracks originated from boundaries of sample and spread parallel to the loading direction until being integrated together. When inclusions have occupied 50% and 25% of sample thickness, four tensile cracks originated from boundaries of sample and spread parallel to the loading direction until being integrated together. Also the inclusion was failed by one tensile crack. The compressive strength of samples decease with the decreases of the inclusions length, and inclusion angle had some effects on that. Failure of concrete is mostly due to the tensile crack. The behavior of crack, was affected by the inclusion length and inclusion number.

• 한국진공학회지
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• 제13권4호
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• pp.175-181
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• 2004

미소인장시험을 통해 304 스테인리스 스틸 판재 위에 증착된 DLC 박막의 안정성을 평가하였다. 모재의 소성 변형과 함께 코팅 층의 손상이 발생하기 시작하는데, 작은 규모의 모재 변형 시에는 인장축의 수직방향으로 박막의 균열이 발생하지만, 모재의 슬립변형이 발생하기 시작하면 인장 축과 $45^{\circ}C$의 각도를 갖는 슬립 면을 따라 필름의 박리가 발생하였다. DLC박막의 박리면적으로부터 필름의 접착력을 평가할 수 있었으며, 필름의 합성 전에 실시하는 Ar 플라즈마 스퍼터링 세척시간이 길수록 그리고 세척시 기판에 인가되는 전압이 높을수록 필름의 접착력은 향상되었다. 이러한 변화는 스테인리스 스틸 모재와 Si 접합 층간의 계면특성이 향상되면, 필름의 전체 접착력을 증진시킬 수 있음을 보여주고 있다.