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박경동(K. D. Park),진영범(Y. B. Jin),류형주(H. J. Ryu),유만희(M. H. Ryu) 한국동력기계공학회 2004 한국동력기계공학회 학술대회 논문집 Vol.- No.-
The lightness of components required on marine and shipbuilding industry is requiring high strength of components. In particular, fatigue failure phenomena, which happen in metal, bring on danger in human life and property. Therefore, antifatigue failure technology takes an important part of current industries. In this study, it was investigated about endurance and fatigue crack propagation rate of according to welding methods of SMAW and FCAW commonly using for welding structures in present. Endurance limit carried out highly in the order of SMAW, FCAW and fatigue crack propagation rate carried out lowly in the order of SMAW, FCAW. By these results, it is needed to used SMAW welding methods for welding structures with small welding capacity and FCAW methods for large welding structures after due consideration about economic gains and operation efficiency of welding. Fatigue crack propagation rate is more effected by strength of welding materials than endurance limit of welding materials according to welding methods.
박경동(K. D. Park),안재필(J. P. An) 한국동력기계공학회 2004 한국동력기계공학회 학술대회 논문집 Vol.- No.-
The lightness of components required in automobile and machinery industry is requiring high strength of components. so this requirement is accomplished as the process of shot-peening method that the compressive residual stress is made on the metal surface. Special research is therefore needed about compressive residual stress on the metal surface in the process of shot-peening method. therefore, in this paper the effect of compressive residual stress of spring steel(JISG SUP-9) by shot-peening on fatigue crack growth characteristics in environment condition(temperature) and mechanical condition(shot velocity, stress ratio)was investigated with considering fracture mechanics. by using the methods mentioned above, the following conclusions have been draw. (I) The fatigue crack growth rate(da/dN) of the Shot-peened material was lower than that of the Un-peened material. And in high temperature, fatigue crack growth rate decreases with increasing temperature. while fatigue crack growth rate increases by decreasing temperature in low temperature. (2) Fatigue life shows more improvement in the Shot-peened material than in the Un-peened material. And compressive residual stress of surface on the Shot-peen processed operate resistance force of fatigue crack propagation.
박경동(K. D. Park),김동욱(D. W. Kim) 한국동력기계공학회 2005 한국동력기계공학회 학술대회 논문집 Vol.- No.-
Antifatigue failure technology take an important the part of current industries. Currently, the shot peening is used for removing the defect from the surface of steel and improving the fatigue strength on surface. In this study, the influence of shot peening and corrosive condition for corrosion property was investigated on immersed in 3.5% NaCl, 10% HN03 + 3% HF, 6% FeC13. The immersion test was performed on two kind of specimen. The immersion periods was performed 90days. Corrosion potential, weight loss were investigated from experimental results.
原子爐用 低合金鋼의 高溫疲勞크랙傳播 特性 및 破壞인성에 관한 硏究
朴卿東(K. D. Park),吳世旭(S. W. Oh),尹漢基(H. K. Yoon) 한국해양공학회 1989 韓國海洋工學會誌 Vol.3 No.1
Fatigue crack growth characteristics and crack closure for an A 508-3 steel were investigated at elevated temperatures(100, 150, 288, and 350℃). The results obtained are summarized as follows ;<br/> 1) While the relation of fatigue crack growth rate da/dN and stress intensity factor range ΔK, is appeared in the linear straight line over the range of da/dN> 5×10<SUP>-9</SUP> m/cycle at 25℃.<br/> That the low fatigue crack propagation rate, experimentically, is appeared at more high temperature region than 25℃.<br/> The crack growth rate da/dN is also increased with increased stress ratios.<br/> 2) Threshold ΔKth is found to be dependent on fretting oxide induced crack closure at 25℃, fretting oxide and oxide scale induced crack closure at 100 crack closure at 288~350℃.<br/> And that the occurrence of fretting oxide induced closure and oxide scale induced crack closure is depended on stress ratios.<br/> 3) The occurrence of oxidation of crack surface that elevated temperature can affect the formation of fretting oxide debris in fatigue crack growth and has an important role on the near-threshold characteristics.<br/> 4) It can be possible to exclude the contrbution due to fretting oxide debris and oxidation at elevated temperature on the near-threshold characteristics by the selection of moderate test temperature.<br/> In this case, the characteristics are controlled only by plasticity induced crack closure and become a structure and environment insensitive material corstant.
박경동(K. D. PARK),김정호(J. H. KIM),윤한기(H. K. Yoon),박원조(W. J. PARK) 한국해양공학회 2001 韓國海洋工學會誌 Vol.15 No.2
Elastic-plastic fracture toughness J<SUB>IC</SUB> can be used as an effective design criterion in elastic plastic fracture mechanics. Most of these systems are operated at high temperature and J<SUB>IC</SUB> values are affected by temperatuere. therefore, the J<SUB>IC</SUB> value at high temperature must be determined for use of integrity evaluation and designing of such systems. Elastic-plastic fracture toughness J<SUB>IC</SUB> tests were performed on SA516/70 carbon steel plate and test results were analyzed according to ASTM E 813-87, ASTM E 813-89 and ASTM E 1152-87. Safety and integrity are required for reactor pressure vessels because, they are operated in high temperature. there are single specimen method, which used as evaluation of safety and integrity for reactor pressure vessels. In this study, elastic-plastic fracture toughness(J<SUB>IC</SUB>) and J-△a of SA 516/70 steel used as reactor pressure vessel steel are measured and evaluated at room temperature, 150℃, 250℃ and 370℃ according to unloading compliance method.