모 연취급장 근로자들의 연폭로지표들과 혈압과의 관련성

임상복,김용배,이용진,리갑수,김화성,황규윤,장봉기,이성수,안규동,이병국 순천향대학교 산업의학연구소 1998 순천향산업의학 Vol.4 No.1

In order to investigate the relationship between blood lead with other lead exposure indices and blood pressure in occupationally lead exposed male workers, 629 workers(515 lead exposed workers and 114 non lead exposed workers) in a storage battery factory were studied. Blood lead(PbB), zinc protoporphyrin(ZPP) and urinary δ-aminolevulinic acid(ALAU) were selected as an index of lead exposure. Height and weight were also meaured with calibrated automatic height-weight machine to produce fatness index directly. Personal information on smoking and drinking history were also collected. Blood pressure was mearured by trained nurses with automatic sphingomanometer. All workers took at least 30 minute rest before their measurement of blood pressure. The results obtained were as follows: 1. The prevalence rate of hypertension of lead exposed and non-exposed workers were 3.5% in both group without any difference. 2. There were no differences of systolic and diastolic pressure between groups divided by lead exposure, smoking habit, drinking habit. but the increase of age group made the difference of diastolic pressure, and only differenct of systolic pressure observed in age group of less than 20 and that of more than 40. 3. In pearson's correlation analysis, PbB was correlated with systolic pressure significantly, but not with diastolic pressure. PbB was also correlated with pressure difference(systolic pressure-diastolic pressure). 4. There were no significant increase of systolic, diastolic pressure and pressure difference by the increase of PbB and ZPP grouping. 5. Stepwise multiple regression analysis using systolic pressure as dependent variable and PbB, ZPP, ALAU, age, work duration, smoking habit, drinking habit and fatness (weight*0.9/height-100) as independent variables, revealed that PbB, age, drinking habit and fatness in order were significantly contributed to the dependent variable. 6. Stepwise multiple regression analysis using diastolic pressure as dependent variable and PbB, ZPP, ALAU, age, work duration, smoking habit, drinking habit and fatness (weight*0.9/height-100) as independent variables, revealed that ALAU, age and fatness in order were significantly contributed to the dependent variable. 7. Stepwise multiple regression analysis using pressure difference as dependent variable and PbB, ZPP, ALAU, age, work duration, smoking habit, drinking habit and fatness(weight*0.9/height-100) as independent variables, revealed that PbB, age and fatness in order were significantly contributed to the dependent variable. 8. Logistic analysis of hypertensive conditions with categorized blood lead and other selected categorized independent variables indicated that only age(40> and 40≤) and fatness(1.0> and 1.0≤) were significantly contributed to dependent variable with 95% significant odd ratio confidence interval. With above results, lead exposure in terms of blood lead seemed to be minimally contributed to the raise of blood pressure, and the effect of blood lead was found to be more prominent on the pressure difference than the systolic and diastolic pressure themselves.

STS304 용접재의 피로거동에 관한 연구

李龍福,鄭鎭成,李柱翰 弘益大學校 科學技術硏究所 1996 科學技術硏究論文集 Vol.7 No.1

In this study, fatigue crack behaviors of STS304 weldment were invesgated when a crack propergated from tensile residual stress region or compressive residual stress region. Crack gowth rates were predicted and compares with experimental result. The experimental results are summarized as follows : 1. For the crack propagation from tensile residual stress region, the maximum residual stress at the crack tip redistributes greater than for the initial residual stress, and the point where the residual stress converted from tension to compression is transferred along the direction of cracking. 2. In the case of fatigue crack propagation from tensile residual stress region, the prediction line of crack growth rate by the initial residual stress declines sharply after middle region and the prediction line by the redistributed residual stress more approaches the experimental results. 3. The fatigue crack from compressive residual stress region has very low fatigue crack growth rate compare with the tensile residual stress region. Because it has low effective stress ratio in compressive residual stress region and it is not almost relaxed compressive residual stress during the cyclic loading. 4. The predicted fatigue crack growth rates considering effects of crack closure are in better agreement with the experimental results, in spite of variation of the residual stress. But there are regions where affected by material properties.

용접방법에 따른 하중전달 십자형 필렛 용접부의 피로특성

이용복,오병덕 한국공작기계학회 2003 한국생산제조학회지 Vol.12 No.1

In this study, endurance limit and fatigue behavior of load carrying fillet welded cruciform joints depending on commonly used welding methods such as SMAW, SAW, MIG and FCAW are investigated. In respect of endurance limit, SMAW specimen showes highest result, and then MIG, SAW, FCAW in descending order. However, SMAW specimen showes lowest crack growth rate and it followed by MIG, FCAW, SAW. By these results, it is needed to use SMAW or MiG welding methods for welding structures with small welding capacity and SAW or FCAW methods for large welding structures with respect to economic benefits and operation efficiency of welding. It was also shown fatigue crack growth rate was more influenced by the strenght of welding materials than the endurance limit of welding materials.

表面缺陷 形狀에 따른 疲勞龜裂進展 特性에 관한 實驗的 硏究

李龍福 弘益大學校 科學技術硏究所 1992 科學技術硏究論文集 Vol.2 No.-

In the current study, a general structural mild steel (SS41) was used of understand the characteristics of fatigue crack and its life evaluation on surface defect, which was machined for surface defect with different shapes. The characteristics of fatigue crack propagation and its life evaluation, during a surface crack initiation from the defect and its propagation, were understood. The experimental results are summarized as follows ; 1. For the surface crack propagation, due to a close relationships between crack length c and depth a, the change in aspect ratio as characteristics of surface crack propagation can be expressed by either the crack depth(a) or the length(c). 2. The aspect ratio of surface crack was varied with fatigue crack propagation. In other words, the ratio was affected by an initial aspect ratio (??) when the thickness ratio (a/t) was 0.4. And then its shape was changed into a semicircular and an ellipitcal one continuously. In this region the ratio the ratio was converged into the following equation regardless of initial defect shape. a/c = 1.4 - 1.43 (a/t) + 0.64 (a/t)² 3. For all initial defect shapes, the total fatigue life on stress ratio R is increased in the case of R=0.3 rather than in R=0.1. It was revealed that the effects of initial defect shape on the total fatigue life of a surface defected member was not constant. 4. In a stable crack growth region (region Ⅱ), the crack growth rates (dc/dN, da/dN) in a direction of length and depth, respectively, as a function of stress intensity factor range ΔK, were scattered over all ΔK range due to the effects of stress ratio R. The effect of stress ratio R were decreased with increase of ΔK. 5. The fatigue crack growth rates (dc/dN, da/dN) and stress intensity factor range ΔK can be related using Paris' equation. The values of index in the equation were in the range 2.54 - 6.89. The values in the direction of length ?? were larger than the value in the direction of depth ??.

고능률 소형 전자석에 의한 자왜 및 자기이방성 측정

이용호,신용돌,김병걸,민복기,송재성 全北大學校 基礎科學硏究所 1994 基礎科學 Vol.17 No.-

자왜 또는 자기이방성의 측정에 사용되는 전사석의 여자전류를 측정에 필요한 수초간만 흘려서 에너지 소모 및 측정시의 최대난점인 시료의 온도변화의 문제를 극소화하였다. 따라서 전자석의 냉각장치는 생략되고 크기와 전원의 용량도 극소화되었다. 공기간격 22㎜, 자극의 단면적 40 × 25㎟에서 0.5 T의 자장발생에는 180 W의 전원으로 족하였다. 시료의 자왜와, 자기이방성에 의한 토크를 전기용량센서에 의하여 측정하여 10^-8의 자왜분해능과 1 nJ의 토크 분해능을 얻었다. 0.02× 0.8× 10㎟의 연자성 리본의 형상이방성을 이용하여 이방성 측정시의 토크값을 교정하였다. A high efficiency small electromagnet(22㎜ air gap and 40 × 25㎟ core's cross section) suitable for measuring magnetostriction and magnetic anisotropy was built. The magnet could be miniaturized by reducing the measuring space and time. The excitation current of the electromagnet was supplied for only a few second of small. An 0.5 T magnetic field was generated with 180 W power consumption. The values of magnetostriction and magnetic anisotropy were measured with a very sensitive capacitance cell with resolution of 10^-8 and 1 no. The torque was calibrated using a soft magnetic ribbon's shape anisotropy.

Al 2024-T4 熔接部의 殘留應力이 疲勞破壞擧動에 미치는 影響

李龍福,金鐘鉉 弘益大學校 1986 弘大論叢 Vol.18 No.2

Fatigue fracture behaviors were investigated by using the TIG welded aluminum alloy such as high-strength Al2024-T4 which are widely used in aero-space industry. The fatigue crack propagation was closely examined in both from tensile residual stress region towards compressive residual stress region and from compressive residual stress region towards tensile residual stress region. The experimental results are summarized as follows: 1. In case of fatigue crack propagation from tensile residual stress region, the values predicted by the Forman equation were found to be exactly corresponded to the experimental values. 2. In case of fatigue crack propagation from compressive residual stress region, the Forman equation was found improper to apply directly, but the equation was found proper, if the stress ratio was modified to zero. 3. It was found that crack propagation speed at tensile residual stress region was greater in restrained welding than in unrestrained welding, While crack propagation speed at compressive residual stress region was the same, both restrained welding and unrestrained welding.

쥐 태자 간의 동굴모세혈관과 적혈구모세포 이주에 관한 전자현미경적 연구

김용욱,김경용,이원복,이흥식 대한해부학회 1998 Anatomy & Cell Biology Vol.31 No.2

고정 스트레스 상태의 흰쥐에서 할로페리돌 전처치가 뇌생아민의 대사에 미치는 영향

이수복,양병환,김이영,이용성,고재경,김광일 漢陽大學校 精神健康硏究 1991 精神健康硏究 Vol.10 No.-

알루미늄合金(A5052-0) 熔接部의 疲勞破壤擧動에 關한 實驗的 硏究

李龍福,元光浩 弘益大學校 1985 弘大論叢 Vol.17 No.2

This research deals with Aluminum-Alloy (A5052-0) weldments. In this research the following conclusions are obtained. 1. when the fatique crack in heat affected zone propagates to base metal zone, total life is long in the following order, base metal, unrestrained weld metal, restrained weld metal, and fatigue crack growth rate is low in the same stress intensity factor range in the following order, base metal, unrestrained weld metal, restrained weld metal. 2. when the fatigue crack in base metal zone propagates to heat affected zone, total fatigue life is long in the following order, restrained weld metal, unrestrained weld metal, base metal, and at first time crack growth rate on base metal is higher than in weld metal but lower at the middle of specimen. 3. In E.C.T. specimen and C.C.T. specimen residual stresses in weldments largely act on fatigue behavior and in E.C.T. specimen mechanical properties of bead zone extend total fatigue life.

SS41村 熔接部의 疲勞龜裂傳播에 미치는 殘留應力의 影響

李龍福,金鍾鉉,趙顯億 弘益大學校 1988 弘大論叢 Vol.20 No.2

In this study submerged arc welded the welding structural steel(SS41) was selected as an application model. On condition that stress ratios were 0.5, 0.3, 0.05, the relaxation of the residual stress was measured according to the number of repeated cycles, and the experimental values were compared with the values expected by the superposition of residual stress relaxation. The result are summarized as follows : 1. Welding residual stress is conspicuously reduced depend on the increase of repeated cycles, that is, the effect of welding residual stress on the crack propagation is gradually reduced with the increase of repeated cycles. 2. The error bet ween the experimental values and expected values which are considered only initial residual stress can be reduced by consideration of residual stress relaxation according to repeated cycles. The expected values depend on this method agree to experimental results of fatigue fracture behavior. 3. In case of welded metal, unlike base metal, rate of initial crack ropagation don't show up large difference because the difference of effective stress ratio(Reff) is decreased very much by addition to tensile residual stress.