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.

AMS 감축과 쌀 수매정책의 효과

이용기,이용복 영남대학교 지역발전연구소 2003 영남지역발전연구 Vol.32 No.-

WTO 규정에 의한 총AMS(aggregate measurement of supports) 감축제약 조건 하에서, 현행 쌀 산업 약정수매제가 쌀 생산 및 농가소득에 미치는 효과를 분석하였다. 이론적 및 실증적 시뮬레이션 분석결과는 정부의 수매가격 인상이 쌀 생산과 생산자의 소득을 반드시 증대시켜 주지는 않는다는 것을 보여주었다. 이런 결과가 나타나게 되는 주요 원인은 정부 수매가격, 즉 지지가격뿐 아니라 시장가격의 생산 의사결정과 농가소득에 상당히 큰 영향을 미치기 때문이다. 즉, 수매가격의 인상은 단기적으로 쌀 생산을 늘리고 그만큼 생산자의 소득을 증대시키는 효과가 있겠지만 총AMS를 감축시켜야 하는 상황에서 이는 결국 초과공급으로 나타나 시장가격의 하락을 초래하여 쌀 생산과 소득증대에 악영향을 미치게 되는 것이다. 특히, 최근 몇 년의 상황처럼 쌀의 재고 누적과 초과공급이 존재하는 상황에서 그 악영향은 더욱 명백해진다. 국내·외의 변화된 시장환경으로 정책효과는 별로 거두지도 못하면서 국제사회로부터 보호주의 정책으로 강한 비난의 대상이 되고 있는 현행 약정수매제도는 재검토되어야 할 시점에 와 있다. WTO에서 녹색정책(Green Box)으로 분류되고 있는 공공비축제로 전환될 필요가 있다.

龜裂닫힘 影響을 考慮한 表面疲勞龜裂 特性에 관한 硏究

李龍福 弘益大學校 科學技術硏究所 1994 科學技術硏究論文集 Vol.4 No.-

In this study, to evaluate the chraracteristics of fatigue crack propagation from the surface of material general structual rolled steel(ss41) was used, which was machined with surface pit shaped defects with different depths and radii. Surface fatigue crack characteristics considered crack closure effect could be well evaluated by experiments. The experimental results are summarized as follows: 1. The surface crack was varied to semicircular shape until a plate thickness ratio reachs 0.4 times and then become semi-elliptical shape. It could be expressed the fatigue crack shape by following equation. ?=1.0-0.67(?)+0.49(?)² 2. As the surface fatigue crack propargate, crack closure effect increases and has maximum value near crack depth with 0.5mm to 2mm and then decreases until it has bean constant value near crack depth ratio with 0.35 to 0.closure factor has 0.87 in the surface direction and 0.9 in the depth direction. 3. Considering the crack closure effect, it could be tacken crack closure ratio. ?=1.04 in both surface direction and depth direction and predicted characteristics of the surface fatigue crack correctly by using it.

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.

中炭素鋼 熔接部의 熱處理에 따른 機械的 性質에 관한 硏究

李龍福,金柄旭,康仁燦 弘益大學校 1982 弘大論叢 Vol.14 No.2

Strength of the weld zone is influenced by many complicated factors, such as welding conditions, constraint, materials, etc. Especially, Residual Stress plays an important role for mechanical properties in the weld zone. In this paper, the stress relief effect on the residual stress of the weld zone was examined under various annealing treatment. The results obtained are as follows. 1.Tensile strength on welding decreased 5.7%, 11.4% and 15.3% with increased annealing temperature from 650℃ to 850℃. 2.Absorbed lmpact energy increased in turns of Bond Zone, Base Metal, Fusion Zone and H.A.Z(Heat Affected Zone) and decreased with increasing of the annealing temperature 650℃, 850℃. 3.Reisdual Stress on welding was reduced by the ratio of 65%, 82.5%, 90% with the increased annealing temperature from 650℃ to 850℃. 4.It may be concluded that the best result of the annealing was obtained at 650℃.

SM45C鋼 熔接部의 殘留應力에 依한 疲勞破壞擧動

李龍福,金鍾鉉,金相準 弘益大學校 1987 弘大論叢 Vol.19 No.2

Fatigue fracture behaviors of submerged arc welded SM45C steel were investigated when a crack propagated from tensile residual stress region. The experimental values were compared with the values expected by the Forman equation. The results are summarized as follows: 1. When the fatigue crack was propagated the experimental values were found to corresponded to the values predicted by Formane quation. 2. The experimental values in weld metals have a little difference to the values expected by Forman equation. It was assumed that residual stresses were relaxed by repeated tensile loading. 3. The higher stress ratios were, the larger the difference of fatigue crack growth rate always were in the Same stress intensity factor range for each stress ratios. Particularly, these differences of fatigue crack growth rates were smaller in weld metal than in base metal. It agrees with the fact of that the difference of .effective stress ratios for each stress ratios is small.

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 ??.

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.

熔接部의 熱處理에 따른 殘留應力 및 破壞擧動에 關한 實驗的 硏究

李龍福,鄭 剛 弘益大學校 1983 弘大論叢 Vol.15 No.2

In this study, picking up a mild steel(SS41) of the carbon steel, a spring steel (SUP9) and stainless steel (SUS304) of the special steel, for the experimental materials, these are welded by CO₂(SS41, SUP9), TIG(SUS304), respectively. After that, the residualstress distribution and fracture behavior at the welded zone are examined according to annealing temperature of the four sections involved as weld. Summarizing of the results in this experiment, the following conclusions are obtained: 1. The residual stress distribution of spring steel (SUP9) is very small in comparison with mild steel (SS41) and stainless steel (SUS304) 2. The removed grade of residual stresses are largest when annealed at 900℃(SS41), 850℃(SUP9), 1000℃ (SUS304), respectively. 3. The tensile strength of heat-affected zones are largest when annealed at 800℃(SS41), as welded(SUP9), 900℃(SUS304), respectively. 4. The impact value of heat-affected zones are largest when annealed at 900℃(SS41), 750℃(SUP9), 1100℃(SUS304), respectively. 5. The best annealing temperatures are at 900℃(SS41), 750℃(SUP9), 1100℃(SUS304), respectively. Then, the residual stress is removed enough and mechanical properties are very suitable.

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.