Development of Wear Model concerning the Depth Behaviour

김형규,이영호,Kim, Hyung-Kyu,Lee, Young-Ho 한국트라이볼로지학회 2005 KSTLE International Journal Vol.6 No.1

Wear model for predicting the vehaviour of a depth is considered in this paper. It is deduced from the energy and volume based wear models such as the Archard equation and the workrate model. A new parameter of the equivalent depth ($D_e$= wear volume /worn area) is considered for the wear model of a depth prediction. A concenpt of a dissipated shear energy density is accommodated for in the suggested models. It is found that $D_e$ can distinguish the worn area shape. A cubic of $D_e$($D_e^3$) gives a better linear regression with the volume than that of the maximmum depth $D_{max}e$($D_{max}^3$) does. Both $D_{max}$ and $D_e$ are used for the presently suggested depth-based wear model. As a result, a wear depth profile can be simulated by a model using $D_{max}$. Wear resistance from the concern of an overall depth can be identified by the wear coefficient of the model using $D_e$.

Improvement and Verification of the Wear Volume Calculation

김형규,이용호,Kim, Hyung-Kyu,Lee, Young-Ho Korean Tribology Society 2005 KSTLE International Journal Vol.6 No.1

A technique for a wear volume calculation is improved and verified in this research. The wear profile data measured by a surface roughness tester is used. The present technique uses a data flattening, the FFT and the windowing procedure, which is used for a general signal processing. The measured value of an average roughness of an unworn surfnce is used for the baseline of the integration for the volume calculation. The improvements from the previous technique are the procedures of the data flattening and the determination of a baseline. It is found that the flattening procedure efnciently manipulates the raw data when the levels of it are not horizontal, which enables us to calculate the volume reasonably well and readily. By comparing it with the weight loss method by using artificial dents, the present method reveals more volume by aroung 3~10%. It is attributed to the protruded region of the specimen and the inaccuracy and data averaging during the weght loss measurement. From a thorough investigation, it is concluded that the present technique can provide an accurate wear volume.

전방충돌경보(FCW)의 교통안전 증진효과 추정

김형규,이수범,이혜린,홍수정,민혜령,Kim, Hyung-kyu,Lee, Soo-beom,Lee, Hye-rin,Hong, Su-jeong,Min, hye-Ryung 한국ITS학회 2021 한국ITS학회논문지 Vol.20 No.2

자율주행의 핵심기술인 첨단 운전자 지원 시스템(Advanced Driver Assistance Systems) 중 대표기술인 전방충돌경보(Forward Collision Warning)를 대상기술로 선정하여, 주행시뮬레이션 실험 기반의 교통사고 예방효과를 추정하였다. 효과척도로 ①인지반응시간(s) ②감속도(m/s2) ③충돌여부(회)로 선정하여, 전방충돌경보 미설치시와 설치시의 변화량 측정하였다. 실험 시나리오는 운전자 전방의 차량의 급정거하는 시나리오(1)과 옆차로에서 차량이 끼어드는 시나리오(2)를 진행하였으며, 주간/야간으로 구분하였다. 분석결과, 전방충돌경보장치를 설치하였을 경우, 인지반응시간(s)이 감소하였으며, 감속도(m/s2)는 감소하였다. 운전자의 위험상황을 빠르게 감지하여 여유로운 감속을 할 수 있게 되었으며, 그에 따른 전방충돌횟수도 감소한 것으로 분석되었다. 향후 운전자의 운전성향을 반영하고 실험 시나리오를 다양화하면, ADAS의 설치효과를 증대시키고 다른 기술의 효과추정에도 활용될 수 있을 것이다. The Forward Collision Warning, a representative technology of the Advanced Driver Assistance Systems, was selected as the target technology. The cognitive response time, deceleration, and impact were selected as the measures of effectiveness. And the amount of change with and without the Forward Collision Warning was measured. The experimental scenarios included a sudden stop event (1) of the vehicle in front of the driver and an event (2) in which the vehicle intervened in the next lane. All experiments were divided into day and night. As a result of the analysis, response time and the deceleration rate decreased when the forward collision warning system was installed. It was analyzed that the driver's risk situation could be detected quickly and the number of front-end collisions could be reduced as a result. Reflecting the driver's operating habits and diversifying the experimental scenarios will increase the installation effectiveness of ADAS and be used to estimate the effectiveness of other technologies.

DEA를 이용한 교통사고 잦은 곳 개선사업 효율성 측정방안 연구

김형규,이수범,엄대룡,원동욱,신소명,Kim, Hyung Kyu,Lee, Soo Beom,Eom, Dae Lyoung,Won, Dong Uk,Shin, So Myoung 한국안전학회 2017 한국안전학회지 Vol.32 No.5

Over the past 30 years, the business effects of the improvement project at black spot have been decreasing since 2010, with a reduction in the amount of government spending, coupled with proposing a uniform improvement plan. In order to promote more efficient improvement projects, it is necessary to evaluate the efficiency of local governments and improve the business methods of local governments with low efficiency. However, more sophisticated efficiency analysis methods are needed. Because in previous studies have been limited to the analysis of effects before and after the project through the simple before-after analysis. For this purpose, this study analyzed the efficiency of improvement project at black spot by local governments in Gyeonggi-do using DEA to compare and analyze efficiency in various fields. As a result, Goyang, Seongnam, Paju, Hanam and Yangju showed high efficiency local governments. For local governmetns with low efficiency, the improvement projets to improve efficiency were divided into civil engineering work, structure work, pavement work, additional work and transportation work, and the appropriate construction ratios of each local government were analyzed and presented.

$37^{\circ}C$에서 incubate 한 가토(家兎) 폐포표면활성물질(肺胞表面活性物質)의 활성도(活性度)의 변화(變化)와 in vitro X 선조사(線照射)의 영향(影響)

김형규,주영은,Kim, Hyung-Kyu,Choo, Young-Eun 대한생리학회 1971 대한생리학회지 Vol.5 No.2

In an attempt to understand the possible effects of temperature and X-irradiation on the activities of surfactant in rabbits, the pulmonary surfactant from the rabbit was subjected to the incubation at $37^{\circ}C$ and X-irradiation with 900r in vitro, and activities of surfactant were measured at 10, 30, 60, and 90 minutes. Tension-area diagram of the lung extract was recorded automatically by the modified Langmuir-wilhelmy balance with a synchronized recording system designed in this Department. A comparison was made with the normal and the following results were obtained. 1) The maximal surface tension, minimal surface tension, width of the tension area diagram at the surface area of 40% and stability index of the normal rabbit lung extract were $31.6{\pm}3.11\;dynes/cm,\;8.2{\pm}0.56\;dynes/cm,\;21.4{\pm}4.40\;dynes/cm\;and\;1.12{\pm}0.22$,respectively. 2) In the $37^{\circ}C$ incubation group, maximal surface tension was similar to the normal value, while minimal surface tension was significantly lower and stability infer was markedly higher than the normal. 3) In the group where X-irradiation of 900r in vitro was applied, maximal surface tension did not differ greatly with the normal or the $37^{\circ}C$ incubation group. The minimal surface tension was significantly lower than the normal but comparing with the $37^{\circ}C$ incubation group, some decrease in minimal surface tension was noted. The width of the tension·area diagram at 40% and stability index in the irradiated group were significantly higher than the normal but a tendency of increase was noted comparing with the $37^{\circ}C$ incubation group.

Ovality를 고려한 원형 관의 탄성 좌굴 방지 설계 방법

김형규(Hyung-Kyu Kim) 대한기계학회 2018 大韓機械學會論文集A Vol.42 No.1

본 논문은 외압을 받는 원형 관의 구조 건전성 요건 중 하나인 탄성 좌굴에 대한 연구이다. 이를 위해 관의 탄성적 성질, 지름 및 두께에 따라 결정되는 임계 좌굴 압력을 분석 도구로 이용하였다. 특히, 단면의 형상 공차로 부여하는 ovality를 고려하였으며, 진원일 때의 임계 좌굴 압력이 ovality의 크기에 따라 감소하는 정도를 평가하는 방법을 제시하였다. 예제로서, Zircaloy-4, Type 304 스테인리스 강 및 냉간 인발된 Cu 재질의 원형 관에 대해, 반경에 대한 두께의 비, 0.04-0.2 그리고 0.5-2.0%의 ovality를 갖는 경우를 분석하였다. 그 결과, 단면이 진원인 경우에 비해 약 15-70%의 임계 좌굴 압력의 감소가 발생하는 것을 발견하였다. 탄성 좌굴을 방지하기 위한 설계 방법으로서 임계 좌굴 압력과 작용 외압의 비인 안전율을 제안하고, 관의 최소 두께를 결정하는 방법을 제시하였다. This paper concerns an elastic buckling of a tube, which is one of the structural integrity requirements. The critical buckling pressure is used as an analysis tool. In particular, ovality is considered as a shape tolerance, and thus a method is proposed to evaluate the influence of the ovality on the reduction of the critical buckling pressure of a perfectly circular cross section. The tubes of Zircaloy-4, Type 304 SST and cold drawn Cu with the thickness to radius ratios of 0.04-0.2, and ovalities of 0.5-2.0% were investigated for an example calculation. It was observed that a considerable reduction of 15-70% occurred owing to the ovality. For design application, a ratio of the critical buckling to external pressures is proposed as a safety factor against the buckling failure, and a method is developed to determine the minimum thickness of the tube to avoid buckling failure.

3D 프린팅 적층의 접촉계면균열 해석을 위한 보정함수의 수렴성

김형규(Hyung-Kyu Kim),김현길(Hyun-Gil Kim) 대한기계학회 2022 대한기계학회 춘추학술대회 Vol.2022 No.3

튜브진동 시 판스프링 지지부의 미끄럼변위와 마멸 분석

김형규(Hyung-Kyu Kim),이영호(Young-Ho Lee),송주선(Ju-Sun Song) 한국트라이볼로지학회 2003 한국트라이볼로지학회 학술대회 Vol.37 No.-

Tube oscillation behaviour is experimentally investigated for the study on the fuel rod fretting that is caused by the flow-induced vibration in nuclear reactor. The experiment was conducted in air at room temperature. The specimen of tube assembly was supported by plate springs which simulated the spacer grids and fuel rods of a fuel assembly. To investigate the influence of contact condition between the grids and rods, normal load of 10 and 5 N, gaps of 0.1 and 0.3 ㎜ were applied. The range of the oscillation at the center of the fuel rod specimen was varied as 0.2, 0.3 and 0.4 ㎜ to simulate the fuel rod vibration due to flow. Displacements near the contact were measured with four displacement sensors during the tube oscillation. As results, the shape of oscillation (phase) varied depending on the contact condition. The oscillation displacement increased considerably from the contact to gap condition. The displacement increased further as the gap size increased. It is regarded that the spring shape influences the tube oscillation behaviour. Simple calculation showed that the slip displacement was very small. Therefore, cumulative damage concept is necessary for the fuel rod wear. The mechanism of plowing is thought required to explain the severe wear in the case of gap existence.

프레팅 피로 균열의 멈춤 조건

김형규(Hyung-Kyu Kim) 대한기계학회 2018 大韓機械學會論文集A Vol.42 No.12

프레팅 피로와 같이 접촉하중과 원거리 피로하중이 작용하는 경우 접촉부 경계에서 발생하여 성장하는 균열의 거동을 이론적으로 해석하고 특히 균열 멈춤 조건을 분석하였다. 균열 진전 거동과 멈춤에 영향을 미치는 인자로서 접촉물체의 접촉부 형상 및 기울어짐, 접촉 전단 하중, 원거리 인장 하중 및 균열의 각도를 고려하였다. 양단이 라운딩된 펀치 형상이 반무한 평판을 누를 때의 접촉 수직 응력을 계산하고 접촉 전단 응력은 수치해석으로 구하였으며 균열 해석을 위해서는 전위밀도함수법을 사용하였다. 해석 결과, 원거리 인장 응력이 작용하지 않고 접촉 하중만 피로로 작용하는 경우 균열은 일정 길이 성장 후 항상 멈추게 되는 것을 알 수 있었다. 따라서, 균열이 성장하여 최종 파단을 가져오기 위해서는 원거리 인장 응력이 필히 부가되어야 한다. 이때 균열 멈춤이 발생할 수 있는 인장 응력의 크기는 각 인자에 따라 달라지며 본 논문은 몇 가지 예제를 통하여 이를 구할 수 있는 방법을 제공한다. This study analyzed the behavior of a surface edge crack subjected to normal and shear contact tractions and far-field bulk fatigue loading. In particular, the conditions of crack arrest were sought in terms of the shape and degree of tilting of an edge-rounding punch, contact shear force, far-field tensile stress, and crack angle. Contact normal tractions in the case of different edge radius sizes were evaluated. Contact shear tractions were obtained using an in-house numerical analysis program. The dislocation density function method was used for the crack analysis. The results show that the crack is always arrested as long as only the contact traction is applied without far-field fatigue loading. Thus, far-field tensile stress is necessary to advance the crack without arrest. The magnitude of the tensile stress to advance the crack depends on the degree of each parameter concerned here. Some example calculations are shown. This work can provide a design tool to avoid fretting fatigue failure.

환상체 씰의 접촉역학적 해석

김형규(Hyung-Kyu Kim),윤경호(Kyung-Ho Yoon),이영호(Young-Ho Lee),김재용(Jae-Yong Kim),이강희(Kang-Hee Lee) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5

Applicability of the contact mechanics theory is investigated for the contact. and internal stresses of a toroidal seal. An actual component of the toroidal seal is an elastomeric O-ring, which is widely used in the mechanical system. Lindley's previous study is consulted to analyze the present problem within the regime of elasticity. Two cases of loading condition are considered: ⅰ) top and bottom of the seal are compressed, and ⅱ) laterally restrained with internal pressure in addition to case ⅰ). As a result, an approximation method for the contact and internal stresses is suggested with accommodating the correction factors of the contact length and peak contact stress to the Hertz formula. A method of experimental verification is discussed.