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Sensitivity analysis of suspension characteristics for Korean high speed train
박찬경,김영국,배대성 대한기계학회 2009 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.23 No.4
The dynamic performance of railway vehicle is normally expressed as stability, safety and ride comfort, and is affected by mass properties, suspension characteristics, contact mechanism between a wheel and a rail, etc. This paper describes the procedure of sensitivity analysis between some of the suspension characteristics of the Korean high speed train (KHST) as the design variables and the dynamic performance as the response variables; and it analyzes the results of sensitivity characteristics for the design variables, comparing two different approximated approach processes known as the response surface model formulated in a polynomial equation and neural network model formulated in a processing code. Analyzing the suspension characteristics for KHST, the approximated method creating meta-models consisted of 29 design variables and 46 performance indexes, which are applied in this paper. The models were coded by using the correlation information between the design variables and the performance indexes made by the 66 times iterative simulations according to the design of experimental method. The table consists of the orthogonal array L32 and the D-Optimal design table. The results show that the proposed sensitivity analysis procedure is very efficient and simply applicable for a complex mechanical system such as railway vehicle system. Also they show that the two models applied in this paper have similar tendency in the view of the sensitivity order of the design variables.
Fe3Al 금속간화합물의 항복강도 이상거동과 변형기구 고찰
박찬경,장영원,전현조 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.8
It is well known that Fe₃Al intermetallic compound shows an anomalous peak of the yield strength at about 500℃. That is, the yield strengths increase with increasing deformation temperature in the range of 300℃-500$quot;℃, and then decrease at higher temperatures. The dislocation structure was examined by transmission electron microscopy, and high temperature mechanical properties were examined by tensile and load relaxation tests. The flow stress curves obtained from lead relaxation bests were then analyzed in terms of internal variable deformation theory. It was found that the flow curves consisted of three micro-deformation mechanisms i.e inelastic deformation mode, plastic deformation mode and dislocation creep deformation mode, depending on both dislocation structure and deformation temperature. The flow curves could be well described by the constitutive equations of these three micro-deformation mechanisms based on the internal variable deformation theory.
Nb 첨가 HSLA 강에 대한 탄질화 석출물의 성장거동
박찬경,강기봉,이원범 대한금속재료학회(대한금속학회) 1996 대한금속·재료학회지 Vol.34 No.6
Growth kinetics of Nb(CN) precipitates have been studied in the 0.03wt.% Nb bearing HSLA steel which was compressively rolled at high temperature(850℃∼1000℃) up to 0.3 strain and isothermally held. Interrupted compression test was also carried out to observe the recrystallization phenomena associated with the precipitation at high temperature. The precipitates were analyzed by the TEM. Observed precipitates revealed that they were nucleated heterogeneously at dislocations and spherical shape. The mean particle size of the precipitates were found to increase with increasing time and temperature. The slope obtained from log plot of precipitate diameter versus time was about 0.5, indicating that the growth behavior followed the Zener's diffusion controlled growth theory. The slope was about 0.3 for the Ostwald ripening region at longer holding time. The nucleation of precipitates was found to retard softening phenomena owing to pinning effect. In ripenening region of precipiates, restart of softening was followed with eliminating of precipitate pinning effect. This result clearly indicate that the growth kinetics of Nb(CN) precipitates affect both the softening and the recrystallization behavior.
C-Mn-Si 계 변태유기소성강의 성형상에 미치는 베이나이트 변태 온도 및 응력상태의 영향
박찬경,전현조,오진후,홍승갑 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.9
The effects of TRansformation Induced Plasticity(TRIP) phenomena on the plastic deformation of 0.2C-1.5Si-1.5Mn multiphase steel have been investigated at various heat treatment and stress conditions. In order to estimate a deformation behavior under multi-axial stress rotate, the hole expansion(HE) tests were carried out. It is shown that the formability evaluation from the uni-axial tensile tests was quite different from the formability measured from multi-axial HE-tests because of different stress state. The formability in the multi-axial stress state decreased due to the extinction of the transformable retained austenite at relatively earlier deformation stage and the production of irregular α' martensite. The voids of TRIP steel were initiated exactly at the interface between transformed martensite and ferrite matrix regardless of stress state. In addition, new form of experimental formula is proposed in order to predict the multi-axial formability of the TRIP steel from the results of uniaxial tensile test.
고강도 9Cr-0.5Mo-1.8WVNb 강의 미세구조와 기계적 특성에 미치는 W 효과
박찬경,홍승갑,이원범 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.9
The microstructure and mechanical properties of high strength 9Cr-0.5Mo-1.8WVNb steel have been investigated to identify the effects of W addition into the 9Cr-1MoVNb steel. The W-added Cr-Mo steel (9Cr-0.5Mo-1.8WVNb) revealed better high-temperature tensile strength regardless of tempering temperature, but exhibited somewhat brittle fracture at higher tempering temperature region, in comparison to those of 9Cr-1MoVNb steel. Transmission electron microscopy also revealed that the evolution of polygonized substructures was delayed by the W addition. The EDS analysis on the structural change of the precipitates, especially (Cr,Fe)₂(C,N), indicated that the W addition increased the ratio of Cr/Fe of (Cr,Fe)₂(C,N), resulting in the stabilization of (Cr,Fe)₂(C,N) through the lattice expansion. It is believed that the stabilized (Cr,Fe)₂(C,N) can enhance the pinning effects on both the movement of dislocation and the growth of lath boundaries. Therefore, it is concluded that the enhanced high-temperature strength of the 9Cr-0.5Mo-1.8WVNb steel is mainly attributed to the retardation of dislocation recovery and the stabilization of carbo-nitrides, caused by the W addition.