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조선 해양 구조물용 강재의 소성 및 파단 특성 IV: 고온 기계적 물성치에 관한 실험적 연구
정준모,임성우,박노식,Choung, Joon-Mo,Im, Sung-Woo,Park, Ro-Sik 한국해양공학회 2011 韓國海洋工學會誌 Vol.25 No.3
This is the fourth of a series of companion papers dealing with the mechanical property reductions of various marine structural steels. Even though a reduction of the elastic modulus according to temperature increases has not been obtained from experiments, high temperature experiments from room temperature to $900^{\circ}C$ revealed that initial the yield strength and tensile strength are both seriously degraded. The mechanical properties obtained from high temperature experiments are compared with those from EC3 (Eurocode 3). It is found that the high temperature test results generally comply with the prediction values by EC3. Based on the prediction of EC3, time domain nonlinear finite element analyses were carried out for a blast wall installed on a real FPSO. After applying the reduced mechanical properties, corresponding to $600^{\circ}C$ to the FE model of the blast wall, more than three times the deflections were observed and it was observed that most structural parts experience plastic deformations exceeding the reduced yield strength at the high temperature. It is noted that a protection facility such as PFP (passive fire protection) should be required for structures likely to be directly exposed to fire and explosion accident.
조선 해양 구조물용 강재의 소성 및 파단 특성 V: 온도 의존성을 고려한 변형률 속도에 관한 실험적 연구
정준모,임성우,김경수,Choung, Joon-Mo,Im, Sung-Woo,Kim, Kyung-Su 한국해양공학회 2011 韓國海洋工學會誌 Vol.25 No.3
This is the fifth in a series of companion papers dealing with the dynamic hardening properties of various marine structural steels at intermediate strain rates. Five steps of strain rate levels (0.001, 1, 10, 100, 200/s) and three steps of temperature levels (LT ($-40^{\circ}C$), RT, and HT ($200^{\circ}C$)) were taken into account for the dynamic tensile tests of three types of marine structural steels: API 2W50 and Classifications EH36 and DH36. The total number of specimens was 180 pieces. It was seen that the effects of dynamic hardening became clearer at LT than at RT. Dynamic strain aging accompanying serrated flow stress curves was also observed from high temperature tests for all kinds of steels. The dynamic hardening factors (DHFs) at the two temperature levels of LT and RT were derived at the three plastic strain levels of 0.05, 0.10, 0.15 from dynamic tensile tests. Meanwhile, no DHFs were found for the high temperature tests because a slight negative strain rate dependency due to dynamic strain aging had occurred. A new formulation to determine material constant D in a Cowper-Symonds constitutive equation is provided as a function of the plastic strain rate, as well as the plastic strain level. The proposed formula is verified by comparing with test flow stress curves, not only at intermediate strain rate ranges but also at high strain rate ranges.
휠로더의 정적/동적 실차 계측 및 강도 평가법에 대한 연구
정준모(Joon-Mo Choung),김규성(Gyu-Sung Kim),장영식(Young-Sik Jang),최익흥(Ick-Hung Choe),허민수(Min-Soo Heo) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.11
This paper presents the static and dynamic measurements for the strength and motion characteristics as<br/> well as the improved procedures to assess strength of wheel loaders. Two scenarios for static measurement<br/> were decided by which cylinder was actuating. The dynamic measurement was performed for two types of<br/> motion, that is, simple reciprocation of the working devices and actual working motion including traveling,<br/> digging and dumping. The measured items were stresses, cylinder pressures and strokes. Stress induced by<br/> bucket working showed higher level than that by boom working. The measured cylinder speeds were<br/> relatively superior to the design speeds. Working stress histories were thought to be closer to static rather than<br/> dynamic. A fully assembled FE model was prepared for structural analysis. In this paper, a more simple<br/> method was suggested to avoid nonlinearity caused by heave of rear frame under digging forces. Also how<br/> brake affected on structural behavior and digging force was examined closely in relation with tire pressure. It<br/> was confirmed that the overall stress level of wheel loader during turning traveling with loaded bucket was far<br/> lower than the yield stress of material.
정준모(Joon-Mo Choung),김규성(Gyu-Sung Kim),장영식(Young-Sik Jang),최익흥(Ick-Hung Choe),허민수(Min-Soo Heo) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4
This paper presents the improved procedure to assess static and dynamic strength of crawler type<br/> excavators. A fully integrated model including front attachment and chassis was prepared for structural<br/> analysis. In this paper, two types of loading input methods were investigated and the method imposing<br/> digging force directly on bucket tooth was more convenient than imposing cylinder reaction force on cylinder<br/> pin even if the two methods showed no discrepancy in analysis results. Static strength analysis was carried out<br/> for eight analysis scenarios based on two extreme digging positions, maximum digging reach position and<br/> maximum digging force positions. The results from static strength analysis were compared with measured<br/> stresses, cylinder pressures and digging forces and showed a good quantitative agreement with measured data.<br/> Dynamic strength analysis was carried out for simple reciprocation of boom cylinders. It was recognized that<br/> the effect of compressive stiffness of hydraulic oil was very important for dynamic structural behavior. The<br/> results from dynamic strength analysis including hydraulic oil stiffness were also compared with measured<br/> acceleration data and showed a qualitative agreement with measured data.
김규성(Gyu-Sung Kim),정준모(Joon-Mo Choung),장영식(Young-Sik Jang),최익홍(Ick-Hung Choe),이준희(Joon-Hee Lee) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4
This paper presents static and dynamic measurement of the stress and motion characteristics for crawler<br/> type excavators. Eight scenarios were prepared for static measurement based on two extreme digging<br/> positions, maximum digging reach position and maximum digging force position. The measured items for<br/> static motion included stress, cylinder pressure, cylinder stroke and digging force. The measured static<br/> stresses showed that asymmetric digging force acting on a bucket induced higher stress level than symmetric<br/> one. The measured static pressures and digging forces also agreed with design pressures and design digging<br/> forces, respectively. The dynamic measurement was performed for two types of motion, that is, simple<br/> reciprocation of each cylinder and actual digging motion. The measured items for dynamic motion were<br/> stroke and pressure of each cylinder, stresses on the working device and acceleration on the upper plate of an<br/> arm. The measured data showed that the natural frequency of the excavator highly depended on the hydraulic<br/> stiffness of cylinders. Digging motion tests revealed that digging motion was closer to static motion rather<br/> than dynamic one.