Metadynamic Recrystallizaton Behavior of a Vanadium-Nitrogen Microalloyed Steel

Zhao Baochun,Zhao Tan,Li Guiyan,Lu Qiang 대한금속·재료학회 2015 METALS AND MATERIALS International Vol.21 No.4

The metadynamic recrystallizaton behavior of a V-N microalloyed steel was studied by performing a two-pass isothermal compression test at 900 °C-1050 °C at a strain rate of 0.1 s-1 to 7 s-1 with the inter-pass time of 0.2-2 s on a Gleeble-3800 thermo-mechanical simulator. The effects of the processing parameters on the metadynamic recrystallizaton behavior of the tested steel were analyzed. The activation energy of the tested steel was determined by regression method and the kinetic models were constructed. Our results showed that the metadynamic recrystallizaton of the tested steel can easily occur due to low activation energy. The effects of the processing parameters are marked and higher deformation temperature, strain rate, or longer time interval contributes to an increase in the metadynamic recrystallized volume fraction. However, it is difficult to observe work hardening in the second pass at a time interval of 0.2 s and stress tends to be steady. Finally, the kinetic models were confirmed by comparing the experimental and the predicted results.

Multiscale singular value manifold for rotating machinery fault diagnosis

Yi Feng,Baochun Lu,Dengfeng Zhang 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.1

Time-frequency distribution of vibration signal can be considered as an image that contains more information than signal in time domain. Manifold learning is a novel theory for image recognition that can be also applied to rotating machinery fault pattern recognition based on time-frequency distributions. However, the vibration signal of rotating machinery in fault condition contains cyclical transient impulses with different phrases which are detrimental to image recognition for time-frequency distribution. To eliminate the effects of phase differences and extract the inherent features of time-frequency distributions, a multiscale singular value manifold method is proposed. The obtained low-dimensional multiscale singular value manifold features can reveal the differences of different fault patterns and they are applicable to classification and diagnosis. Experimental verification proves that the performance of the proposed method is superior in rotating machinery fault diagnosis.

Detecting the weak damped oscillation signal in the agricultural machinery working environment by vibrational resonance in the duffing system

Suzhen Wang,Baochun Lu 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.12

The working environment for agricultural machinery is complex and variable. Some weak characteristic damped oscillation signals are extremely difficult to extract and analyze because of their long-term operation in a strong noise environment. The vibration resonance (VR) phenomenon of a second-order Duffing bistable system driven by a weak characteristic damped oscillation signal and a high-frequency harmonic signal was studied. The results indicate that the cooperation between the Duffing damping ratio and attenuation coefficient can induce the VR occurrence of a small-parameter damped oscillation signal. As a result, the energy of the weak characteristic signal becomes stronger, and the VR numerical processing method of the high-frequency weak characteristic damped oscillation signal is provided. On this basis, aiming at the strong noise of agricultural machinery working, taking the weighted kurtosis index as the objective function and supplemented by variational mode decomposition (VMD) technology, a VR-VMD adaptive method based on quantum particle swarm optimization (QPSO) was proposed to extract the weak characteristic damped oscillation signal. Numerical simulation analysis and experiments show that the proposed VR-VMD method is effective in a strong noise environment for agricultural machinery.

The structural performance of axially loaded CFST columns under various loading conditions

Fuyun Huang,Xinmeng Yu,Baochun Chen 국제구조공학회 2012 Steel and Composite Structures, An International J Vol.13 No.5

Concrete filled steel tube (CFST) structures have been used widely in high-rise buildings and bridges due to the efficiency of structurally favourable interaction between the steel tube and the concrete core. In the current design codes only one loading condition in the column members is considered, i.e., the load is applied on the steel tube and concrete core at the same time. However, in engineering practice the tube structures may be subjected to various loading conditions such as loading on the concrete core only, preloading on the steel tube skeleton before filling of concrete core, and so on. In this research, a series of comparative experiments were carried out to study the structural performance of concrete filled circular steel tube columns subject to four concentric loading schemes. Then, a generalized prediction method is developed to evaluate the ultimate load capacity of CFST columns subject to various loading conditions. It is shown that the predictions by the proposed method agree well with test results.

Analysis of local vibrations in the stay cables of an existing cable-stayed bridge under wind gusts

Qingxiong Wu,Kazuo Takahashi,Baochun Chen 국제구조공학회 2008 Structural Engineering and Mechanics, An Int'l Jou Vol.30 No.5

This paper examines local vibrations in the stay cables of a cable-stayed bridge subjected to wind gusts. The wind loads, including the self-excited load and the buffeting load, are converted into time-domain values using the rational function approximation and the multidimensional autoregressive process, respectively. The global motion of the girder, which is generated by the wind gusts, is analyzed using the modal analysis method. The local vibration of stay cables is calculated using a model in which an inclined cable is subjected to time-varying displacement at one support under global vibration. This model can consider both forced vibration and parametric vibration. The response characteristics of the local vibrations in the stay cables under wind gusts are described using an existing cable-stayed bridge. The results of the numerical analysis show a significant difference between the combined parametric and forced vibrations and the forced vibration.

Influence of cable loosening on nonlinear parametric vibrations of inclined cables

Qingxiong Wu,Kazuo Takahashi,Baochun Chen 국제구조공학회 2007 Structural Engineering and Mechanics, An Int'l Jou Vol.25 No.2

The effect of cable loosening on the nonlinear parametric vibrations of inclined cables is discussed in this paper. In order to overcome the small-sag limitation in calculating loosening for inclined cables, it is necessary to first derive equations of motion for an inclined cable. Using these equations and the finite difference method, the effect of cable loosening on the nonlinear parametric response of inclined cables under periodic support excitation is evaluated. A new technique that takes into account flexural rigidity and damping is proposed as a solution to solve the problem of divergence. The regions of inclined cables that undergo compression are also indicated.

Dynamic characteristics of cable vibrations in a steel cable-stayed bridge using nonlinear enhanced MECS approach

Wu, Qingxiong,Takahashi, Kazuo,Chen, Baochun Techno-Press 2008 Structural Engineering and Mechanics, An Int'l Jou Vol.30 No.1

This paper focuses on the nonlinear vibrations of stay cables and evaluates the dynamic characteristics of stay cables by using the nonlinear enhanced MECS approach and the approximate approach. The nonlinear enhanced MECS approach is that both the girder-tower vibrations and the cable vibrations including parametric cable vibrations are simultaneously considered in the numerical analysis of cable-stayed bridges. Cable finite element method is used to simulate the responses including the parametric vibrations of stay cables. The approximate approach is based on the assumption that cable vibrations have a small effect on girder-tower vibrations, and analyzes the local cable vibrations after obtaining the girder-tower responses. Under the periodic excitations or the moderate ground motion, the differences of the responses of stay cables between these two approaches are evaluated in detail. The effect of cable vibrations on the girder and towers are also discussed. As a result, the dynamic characteristics of the parametric vibrations in stay cables can be evaluated by using the approximate approach or the nonlinear enhanced MECS approach. Since the different axial force fluctuant of stay cables in both ends of one girder causes the difference response values between two approach, it had better use the nonlinear enhanced MECS approach to perform the dynamic analyses of cable-stayed bridges.

Behavior of UHPC-RW-RC wall panel under various temperature and humidity conditions

Wu, Xiangguo,Yu, Shiyuan,Tao, Xiaokun,Chen, Baochun,Liu, Hui,Yang, Ming,Kang, Thomas H.K. Techno-Press 2020 Advances in concrete construction Vol.9 No.5

Mechanical and thermal properties of composite sandwich wall panels are affected by changes in their external environment. Humidity and temperature changes induce stress on wall panels and their core connectors. Under the action of ambient temperature, temperature on the outer layer of the wall panel changes greatly, while that on the inner layer only changes slightly. As a result, stress concentration exists at the intersection of the connector and the wall blade. In this paper, temperature field and stress field distribution of UHPC-RW-RC (Ultra-High Performance Concrete - Rock Wool - Reinforced Concrete) wall panel under high temperature-sprinkling and heating-freezing conditions were investigated by using the general finite element software ABAQUS. Additionally, design of the connection between the wall panel and the main structure is proposed. Findings may serve as a scientific reference for design of high performance composite sandwich wall panels.

Influence of cable loosening on nonlinear parametric vibrations of inclined cables

Wu, Qingxiong,Takahashi, Kazuo,Chen, Baochun Techno-Press 2007 Structural Engineering and Mechanics, An Int'l Jou Vol.25 No.2

The effect of cable loosening on the nonlinear parametric vibrations of inclined cables is discussed in this paper. In order to overcome the small-sag limitation in calculating loosening for inclined cables, it is necessary to first derive equations of motion for an inclined cable. Using these equations and the finite difference method, the effect of cable loosening on the nonlinear parametric response of inclined cables under periodic support excitation is evaluated. A new technique that takes into account flexural rigidity and damping is proposed as a solution to solve the problem of divergence. The regions of inclined cables that undergo compression are also indicated.

Dynamic Characteristics of Megami Cable-stayed Bridge- A Comparison of Experimental and Analytical Results-

Qingxiong Wu,Yuichi Kitahara,Kazuo Takahashi,Baochun Chen 한국강구조학회 2008 International Journal of Steel Structures Vol.8 No.1

The Megami Bridge, with a main span of 480 m, is the 6th longest cable-stayed bridge in Japan. A comparison of experimental and analytical modal analysis is performed to determine the dynamic characteristic of this bridge. The ambient vibration test is carried out using very few accelerometers. Parameter identification is carried out using the stochastic subspacebased identification (SSI) method in the time-domain as proposed by Katayama. The SSI method used in this paper can be used for estimating the modal properties of a long span cable-stayed bridge by comparing with the maximum entropy method(MEM). Furthermore, the effectiveness of the tuned mass dampers (TMDs) used in the bridge is evaluated through a human excitation test. Logarithmic damping is about 0.030 when the TMD is activated, a little higher than the design value 0.026, so proving that the TMDs are effective. Finally, the analytical eigenvalues obtained from finite element analysis agree well with the experimental values, thus verifying the analytical model.