排序方式: 共有56条查询结果,搜索用时 62 毫秒
1.
GAO Rong WANG Xiaojing School of Mechanical Electronic Engineering Automation Shanghai University Shanghai China WANG Min No. Institute Shanghai Academy of Spaceflight Technology Shanghai China YU Maohua XIE Mingchun School of Mechanical Electronic Engineering Automation Shanghai University Shanghai China 《机械工程学报(英文版)》2007,20(3):75-78
The nonlinear dynamics of the lateral micro-resonator including the air damping effect is researched. The air damping force is varied periodically during the resonator oscillating, and the air damp coefficient can not be fixed as a constant. Therefore the linear dynamic analysis which used the constant air damping coefficient can not describe the actual dynamic characteristics of the mi-cro-resonator. The nonlinear dynamic model including the air damping force is established. On the base of Navier-Stokes equation and nonlinear dynamical equation, a coupled fluid-solid numerical simulation method is developed and demonstrates that damping force is a vital factor in micro-comb structures. Compared with existing experimental result, the nonlinear numerical value has quite good agreement with it. The differences of the amplitudes (peak) between the experimental data and the results by the linear model and the nonlinear model are 74.5% and 6% respectively. Nonlinear nu-merical value is more exact than linear value and the method can be applied in other mi-cro-electro-mechanical systeme (MEMS) structures to simulate the dynamic performance. 相似文献
2.
R. González-Martínez 《金属学报(英文版)》2007,20(4):235-240
The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke. 相似文献
3.
《Tribology - Materials, Surfaces & Interfaces》2013,7(3):110-117
AbstractIn this paper, the general dynamic Reynolds equation of sliding–squeezing surfaces of exponential shaped slider bearings with micropolar fluid is solved numerically for the assessment of dynamic characteristics. The two Reynolds type equations governing the steady performance and the perturbed characteristics are obtained using the perturbation technique and are solved numerically using the finite difference method. The results are compared with that of the inclined plane slider bearing. It is found that the exponential shaped slider bearing lubricated with micropolar fluids results in higher steady state film pressure, load carrying capacity and better dynamic stiffness and damping characteristics. 相似文献
4.
《Science & Technology of Welding & Joining》2013,18(4):357-362
AbstractThe study on the vertical and horizontal spot vibration welding of Inconel 690 alloy was carried out to observe the dendrite morphologies and estimate the temperature gradient G and growth rate R under different vibration conditions. The purpose is to further understand the mechanism of microstructure changes under vibration. Based on different temperature distributions along vertical and horizontal directions in the centre of a melting pool, it is found that vertical and horizontal vibrations induce the divergence of the nucleates site and grain growth rate then affect the grain morphologies. Vertical vibration welding creates a coarse dendrite structure with sturdy secondary and tertiary dendrite arms, and the X-ray diffraction (XRD) profile of this structure shows a strong (200) peak. Horizontal vibration welding results in grain refinement and a relatively disordered structure, which is reflected by its low XRD intensity. The study shows that vibration affects the weld structure by improving nucleates and changing growth rate. 相似文献
5.
《Science & Technology of Welding & Joining》2013,18(5):443-450
AbstractVibration welding is a process used to join thermoplastic components. Currently, under optimised low pressure welding, the weld strength of butt joints of unreinforced polymer can be equivalent to the strength of unwelded material. However, in short glass fibre reinforced polymer, the optimised weld strength is significantly lower than that of unwelded material and is closer to the strength of the resin matrix. This lower strength is attributable to the unfavourable orientation of the short glass fibres in the weld zone. The fibres tend to align parallel and in the plane of the weld zone and thus provide no reinforcement in the direction perpendicular to the weld zone. In the present work the impact of various modifications to the existing vibration welding technology was examined, with the objective of increasing the current achievable weld strength of glass reinforced nylon. The introduction of a secondary vibratory motion perpendicular to the weld plane during welding resulted in strengths 20% higher than those of samples welded using the standard vibration welding process. 相似文献
6.
《Science & Technology of Welding & Joining》2013,18(3):335-338
AbstractVibration of welded parts is usually applied to achieve effects similar to thermal stress relief. With vibration, it is not only residual stresses that are affected. Using two different welding processes, the influence of vibration on hardness and toughness of the weld was measured. For each welding process, two series of Charpy specimens were made over the temperature range from -60 to +20°C. The only difference between the two series was in performing welding with or without vibration. Slight differences in weld metal hardness were observed. Toughness measurements show an increase in impact toughness and a significant increase in fracture toughness in samples which were vibrated during welding. 相似文献
7.
《成像科学杂志》2013,61(2):107-108
AbstractHolographic interferometry has been applied to in situ measurements of vibration fields of large diameter conduits undergoing unsteady internal excitations. The ambient conditions under which the measurements were carried out were extremely difficult. The measurements, covering an area of several square meters with each holographic recording, were performed using a portable one joule pulsed ruby laser system capable of producing two sequential Q-switched pulses each with duration of ~25 ns with a variable pulse separation between 10 and 800 μs. The entire assembly of laser and holographic camera was constructed as a single unit incorporating an internal reference beam; the reference beam included a mirror with the facility to make an angular tilt between the two laser pulses with the objective of providing a facility to obtain information relating to the phase of antinodes within the recorded area of the hologram. 相似文献
8.
《Canadian Metallurgical Quarterly》2013,52(2):179-184
AbstractThe effect of surfactants nonylphenolpolyethylene glycol with molecular weight 900 (D1), dinaphthylmethane-4,4'-disulphonic acid (D2) and polyethylene glycol with molecular weight 400 (D3) on both cobalt-zinc dust cementation kinetics and the structure of obtained deposits was investigated in the presence of copper or antimony. The reaction of cobalt cementation was found not to follow first-order kinetics due to the hydrogen evolution which takes place along with cementation reaction.Two rate regions were observed. Surfactants D1 and D3 inhibit but D2 has no effect on cobalt cementation rate. Copper increases but antimony decreases cobalt deposition. On the other hand, the presence of antimony substantially increases the inhibition effect of D1 and D3 on cobalt cementation. A higher temperature improves cobalt cementation.D1 and D3 inhibit antimony cementation.The effect of D1 is substantially higher and contributes to a large decrease of antimony deposition by zinc dust.The influence of copper and antimony on the structure of obtained deposits is strikingly different. The presence of copper causes the deposition of coarser products containing massive formations of lamellar crystallites. The addition of antimony contributes to the formation of compact uniform layers of deposits with a low porosity on the surface of zinc particles. Surfactants D1 and D3 decrease the crystallite size and deposit porosity and their effect is substantially larger in the presence of antimony. The lowest porosity is found in the presence of both D1 and antimony.According to the obtained results, the concentration of antimony during the cobalt cementation by zinc dust from the solutions containing surfactants D1 and D3 must be lower than that of copper.On a étudié l'effet d'agents de surface sur la cinétique de cémentation de la poussière de cobaltzinc et sur la structure des dépôts obtenus, en présence de cuivre ou d'antimoine. Les agents étudiés incluent le glycol nonylphénolpolyéthylénique, avec un poids moléculaire de 900 (D1), l'acide dinaphthylméthane-4,4'-disulfonique (D2) et le polyéthylène-glycol, avec un poids moléculaire de 400 (D3). On a trouvé que la réaction de cémentation du cobalt ne suivait pas une cinétique de premier ordre à cause du dégagement d'hydrogène qui se produit en même temps que la réaction de cémentation. On a observé deux régions avec différents taux. Les agents de surface D1 et D3 inhibent le taux de cémentation du cobalt, mais le D2 n'a aucun effet sur celui-ci. Le cuivre augmente la formation de cobalt mais l'antimoine la réduit. D'un autre côté, la présence d'antimoine augmente substantiellement l'effet d'inhibition du D1 et du D3 sur la cémentation du cobalt. Une température plus élevée améliore la cémentation du cobalt.Le D1 et le D3 inhibent la cémentation de l'antimoine. L'effet du D1 est substantiellement plus élevé, contribuant à une grande diminution de la formation d'antimoine par la poussière de zinc.L'influence du cuivre et de l'antimoine sur la structure des dépôts obtenus est remarquablement différente. La présence de cuivre entraîne la formation de produits plus grossiers contenant des structures massives de cristallites lamellaires. L'addition d'antimoine contribue à la formation de couches uniformes compactes de dépôts ayant une faible porosité à la surface des particules de zinc. Les agents de surface D1 et D3 diminuent la taille de cristallite et la porosité du dépôt et leur effet est substantiellement plus important en présence d'antimoine. La porosité la plus faible se trouve en présence simultanée du D1 et de l'antimoine.D'après les résultats obtenus, la concentration de l'antimoine, lors de la cémentation du cobalt par la poussière de zinc à partir de solutions contenant les agents de surface D1 et D3, doit être plus faible que celle de cuivre. 相似文献
9.
《Materials Science & Technology》2013,29(11):1389-1396
AbstractThe objective of the present work was to investigate the effect of presence of SiC reinforcement and the vibration frequency on the overall damping characteristics of pure magnesium. The testing method uses a combination of the modified free – free beam method coupled with a circle fit approach. The effect of frequency on the damping property was studied by adding end masses to the specimen so as to alter the resonant frequency of the suspended beam. In the present study, the results are compared against a monolithic magnesium sample. The results revealed a higher damping capability of the composite specimen at all tested frequencies when compared to monolithic magnesium. Both monolithic and reinforced magnesium showed a progressive decrease in damping with an increase in frequency. An attempt is made to rationalise the damping behaviour of the composite in terms of the presence of a process induced plastic zone at the matrix/particulate interface and the operating frequency. 相似文献
10.
《Materials Science & Technology》2013,29(7):931-934
AbstractThe traditional materials encounter difficulties to comply with all the properties required by new components under service conditions. The automotive and the railway industries require low cost solutions to improve the final performance of components made from steel, cast iron, or even conventional aluminium alloys (e.g. clutch discs, brake discs, or pistons). Weight reduction, improvement in wear behaviour, high thermal conductivity, low coefficient of thermal expansion, and easy recycling are sought, among other characteristics, in order to obtain more efficient products leading to a reduction of pollutant emissions. The range of materials that can meet these requirements is presently very narrow and their final price is more expensive (e.g. aluminium matrix composites) than currently used materials. In this paper a new low cost metal matrix composite that has been used to produce pistons, clutch discs, and train brake discs is presented. 相似文献