Applied Mechanics and Materials Vol. 151

Abstract: The sensor fault diagnosis method based on wavelet packet characteristic entropy and relevance vector machine are researched, which is used on engine test bed . In detail, the wavelet packet characteristic entropy is applied for feature extraction to get the feature matrix which denote all kinds of known working status of sensor, and the feature matrix are encoded; The feature matrix as inputs and feature codes as outputs are proposed for training the relevance vector machine classifier to get the optimum parameters. In the fault diagnosis unit, it uses the wavelet packet characteristic entropy to acquire the on-line feature matrix of sensor. The on-line feature matrix is supplied to the trained relevance vector machine classifier as inputs to validate the working status of sensor. An application of the method in engine test bed system is introduced. Finally, the applicability and effectiveness of the method is illustrated by experiments

Abstract: Water-jet guided laser processing is a kind of material processing technology using variable-length water jet optical waveguide. In this paper, by means of the finite element method (FEM), the simulation on drilling with water-jet guided laser was carried out based on thermal effect of laser and mechanical effect origining from shock pressure of shock wave caused by heat-induced explosion and impact of high-speeds water jet. The results show that evaporation and mechanical ablation of molten material is the main form of the material removal, the mechanical effect only contributes the slight deformation to the material with temperature gradient, the rapid water jet cooling after laser pulse played a quenching role in the processing area. In addition, the paper also analyzed the variable tendency of the impact of water jet to workpiece and clarified the scope and trend of the role of water jet.

Abstract: NC code to machine arc-surface of the transmission box had been obtained in UG CAM module. Then, the code was imported into Vericut in order to control the virtual machine to mill the box’s arc-surface. As a result, the simulation process machining the typical arc-surface of the transmission box was achieved. Meanwhile, the collision and interference were all verified as well. The accuracy of NC code was not only tested but also modified in this process. Due to this work has been finished, the production cost will be decreased and the production cycle will be shortened. It is of great guiding significance for the actual production process.

Abstract: Based on initial discontinuity state (IDS) of material, this paper presents a preliminary analytical model which was developed to evaluate the effect of exfoliation corrosion on the residual fatigue life of upper wing skins. A life prediction was then carried out using constant amplitude compression dominated loading for various exfoliation corrosion levels by AFGROW, and the prediction agreed reasonably with the available test data. The result suggest that exfoliation can be treated as a process zone located initially at a surface, and then at the base of an evolving general stress concentration representing the loss of material in the exfoliation region. The major effect of the exfoliation corrosion on fatigue life is to cause a dramatic reduction in life with small corrosion depths, and most of the fatigue effect is associated with the introduction of small pits, rather than more general stress concentration associated with the bulk of the exfoliation attack. But the effect of pit on fatigue life is gradually reduced with increasing pit size. A pit with a constant depth can be applied to the model described in this paper for long exposure structure. A preliminary recommendation for the pit depth is about 0.3mm for LY12CZ.

Abstract: The four-point bending method and weight loss method were used to study respectively the stress corrosion cracking behavior and weightlessness corrosion situation of the baosteel BG80S steel in the simulated field environments. The experimental results shown that BG80S won't occur to stress corrosion cracking when the maximum loading stress is 85% Rt0.5 ; the corrosion rates increase with the rising of temperature which is from 40°C to 80°C under the dynamic and static conditions of the simulated environments; the dynamic corrosion rates are between 1.5558 and 1.7523mm/a and the corrosion rates are 0.4827～1.4078mm/a under the static conditions, both of which belong to a serious corrosion category; the form of corrosion is uniform corrosion under the dynamic conditions; because the corrosion products exist micro defects under the static conditions of 80°C, the experimental samples have had the localized corrosion.

Abstract: The Cu-30wt%Ag alloy nanopowders are prepared by induction plasma technology, and the nanopowder is successfully coated by terpineol (C10H18O). The morphology, phase composition and oxidation resistance of nanopowders are characterized by scanning electron microscopy (SEM), X-ray diffraction and thermogravimetric (TG) analysis. When the suitable processing parameters of induction plasma are chosen, the spherical morphology and average diameter about 89 nm of Cu-30wt%Ag nanopowders are obtained. Meanwhile, the Cu-Ag alloy nanopowders which are coated by terpineol are free from oxidation when temperature is below 280°C.

Abstract: The fractal tree-shaped structure such as tree, plant root, leaves, animal lung and so on is universal and unique in nature. These structures possess the symmetric micro-channel distributions and the efficient transport characteristics. They are considered to be an optimal network channel of mass transfer and heat transfer. The mass transfer and heat transfer feature of bipolar plate in proton exchange membrane fuel cell (PEMFC) is similar with animal lungs and leaves. In this paper, fractal theory is used to study tree-shaped flow field structure of bipolar plate in PEMFC. It is demonstrated by numerical simulation that fractal tree-shaped flow field structure can provide substantially flow-field distribution, current density and heat transfer compared to the traditional flow field structure.

Abstract: The working principle of the micro-CHP based on biomass direct-fired Stirling engine and the thermal energy conversion process of the biomass direct-fired fuels were analyzed. On the basis of analysis, a 1kW β-type Stirling generator was designed and constructed for lab tests. Then, experiments were carried out to evaluate the effectiveness of the prototype. Through the analysis of experimental data and simulation, the change law of charge voltage, charge current with the engine speed and pressure, as well as the relation of heat and electricity, the power generation efficiency and the overall efficiency of the thermoelectric in the working process was obtained. The results showed that biomass energy use efficiency will be improved through the use of micro-CHP based on biomass direct-fired Stirling engine.

Abstract: This paper analyzed the eddy characteristics of the coaxial cylindrical magnetic coupler by using the finite element method, and simulated the impact of eddy currents on magnetic field. These effects mainly reflected in: weakening the magnetic coupling of the magnetic field intensity, and reducing the magnetic coupling torque. In addition, this paper calculated eddy current power loss, and proposed specific programs to reduce the eddy current power loss.