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李時泳,郭東勳,金昌浩 동국대학교 농림과학연구소 1994 農林科學 論文集 Vol.18 No.-
The purposes of this study are to analyze environmental factors affecting the behavior of forest fires, were surveyed 25 burned areas over country. The obtained results were as follows : 1. Wind velocity at the burned area was highest at the area of mountain ridge and became slower in the order of the area of middle, foothill, and opposite side of the slope. The seriousness of the damage was proportionate to wind velocity. 2. Most of the suppression lines were located at the mountain ridge and downslope with 43 and 24 percent out of total survey area respectively. Fires were mostly contained by helicopters where suppression lines located at mountain ridge and upgoing slope, and was contained by ground fire fighters at the area of valley and downslope, but with exceptions stopped spontaneously. 3. The shape of burned areas differed depending on topography, wind direction, and wind velocity. But most of the burned area showed simple upslope type in Korea. 4. Factors affecting burning behavior and rate of fire prediction equations are effective in the order of height of mountain, amount of rainfall before burning, maximum wind speed. The burned area was calculated by Y=0.10X_1+7.1X_2+5.4X_3-49.0(R^2=0.58**). (Y=Burned area(㏊), X_1=Height of mountain(m), X_2=Amount of rainfall before burning(㎜), X_3=maximum wind speed(㎧)) 5. The Correlation between the burned area(Y) and rate of spread(X) were intimated and the relationship was found by the following equation : Y=0.10X-3.60(R^2=0.90**) (Y=Burned area(㏊), X=Rate of spread(mim.))
Effect of heat treatment residual stress on stress behavior of constant stress beam
Kwak, Si Young,Hwang, Ho Young Society for Computational Design and Engineering 2018 Journal of computational design and engineering Vol.5 No.1
Although most casting and heat treatment processes generate significantly high residual stress in the products, this factor is generally not taken into account in the design stage of the product. In this study, experimental study and numerical analysis were conducted on a constant stress beam to examine effects of the residual stress generated during the heat treatment process on yielding behavior of the product in use. A constant stress beam of SUS 304 was designed in order to test the stress behavior related to residual stress. The residual stresses generated during quenching heat treatment of the beam were measured in advance by ESPI (Electronic Speckle-Pattern Interferometry) equipment, and then the external stresses generated while applying a simple external load on the beam were measured. Also, the residual stress distribution generated during the heat treatment process was computed using a numerical analysis program designed for analyzing heat treatment processes. Then, the stress distribution by a simple external load to the beam was combined with the calculated residual stress results of the previous heat treatment step. Finally, the results were compared with experimental ones. Simulation results were in good agreement with the experimental results. Consistency between experimental results and computational results prove that residual stress has significant effects on the stress behavior of mechanical parts. Therefore, the residual stress generated in the previous heat treatment step of casting must be taken into account in the stage of mechanical product design.
Effect of heat treatment residual stress on stress behavior of constant stress beam
Si Young Kwak,Ho Young Hwang 한국CDE학회 2018 Journal of computational design and engineering Vol.5 No.1
Although most casting and heat treatment processes generate significantly high residual stress in the products, this factor is generally not taken into account in the design stage of the product. In this study, experimental study and numerical analysis were conducted on a constant stress beam to examine effects of the residual stress generated during the heat treatment process on yielding behavior of the product in use. A constant stress beam of SUS 304 was designed in order to test the stress behavior related to resid-ual stress. The residual stresses generated during quenching heat treatment of the beam were measured in advance by ESPI (Electronic Speckle-Pattern Interferometry) equipment, and then the external stresses generated while applying a simple external load on the beam were measured. Also, the residual stress distribution generated during the heat treatment process was computed using a numerical analysis pro-gram designed for analyzing heat treatment processes. Then, the stress distribution by a simple external load to the beam was combined with the calculated residual stress results of the previous heat treatment step. Finally, the results were compared with experimental ones. Simulation results were in good agree-ment with the experimental results. Consistency between experimental results and computational results prove that residual stress has significant effects on the stress behavior of mechanical parts. Therefore, the residual stress generated in the previous heat treatment step of casting must be taken into account in the stage of mechanical product design.
곽시영(Si-Young Kwak),임채호(Chae-Ho Lim),백재욱(Jae-Wook Baek) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
Most structure engineers give the casting components over-estimated factor of safety without any reasonable foundation due to the worries about the unavoidable defects such as shrinkages and porosity in castings; the engineers have little knowledge on the relation between the defect and structural behavior. And the workers in casting field also do not know how to control the defects by manufacturing; they do not know to where the defects move or until how size they reduce the defects. In this study, shrinkage defect was scanned by industrial computerized tomography instrument (CT), and subsequently was modeled to a spheroid primitive for structural analysis. Using these simplified models of shrinkage, we observed the effects of the defect on the results of the structural analysis. A commercial structural analysis code was used to do the analysis works. Considering the conclusions, it is possible to manage the shrinkages effectively in casting process and to design the products with more reliable
내부 결함을 고려한 주조 제품의 피로수명 예측을 위한 결함 형상단순화 해석모델
곽시영(Si-Young Kwak),김학구(Hak-Ku Kim) 대한기계학회 2011 大韓機械學會論文集A Vol.35 No.10
내부결함은 주조제품의 강도 및 피로 수명에 있어 상당한 영향을 미치기 때문에 주조공정에서 주요 관심사 이다. 일반적으로 내부결함은 응력집중을 발생시키며 균열의 시작점이 되므로 피로 수명과 같은 기계적 거동에 있어 수축공과 같은 결함을 이해하는 것이 중요하다. 본 논문에서는 내부결함을 고려한 인장시편에 대해 피로시험을 수행하고 주조결함을 고려할 때의 특정하중피로노치 계수를 산정하였다. 실제 내부결함은 산업용 CT 장비를 통해서 확인하였으며 확인된 결함은 형상단순화법에 의해 타원체로 단순화 하고 응력해석과 피로해석을 수행하였다. 그 결과 우리가 제안한 방법이 기계적 거동에 있어 내부결함의 영향을 조사하고 피로수명 등을 예측함에 있어 유용함을 확인할 수 있었다. Internal defects are a major concern in the casting process because they have a significant influence on the strength and fatigue life of casting products. In general, they cause stress concentration and can be a starting point of cracks. Therefore, it is important to understand the effects of internal defects on mechanical properties such as fatigue life. In this study, fatigue experiments on tensile specimens with internal defects were performed. The internal defects in the casting product were scanned by an industrial CT scanner, and its shape was simplified by ellipsoidal primitives for the structural and fatigue analysis. The analysis results were compared with experimental results for casting products with internal defects. It was demonstrated that it is possible to consider internal defects of casting products in stress and fatigue analysis. The proposed method provides a tool for the prediction of the fatigue life of casting products and the investigation of the effects of internal defects on mechanical performance.