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The sound field model of an irregular enclosure with two elastic walls and an inclined wall is established by the modal theory. The modal parameters of the irregular enclosure are obtained by the envelope rectangular technique. The influence of the inclination wall angle on the sound field in the irregular enclosure is discussed. When the inclination angle is increased from 0° to 45°, the resonance frequencies of the acoustic enclosure are basically reduced in the frequency range of 0∼250 Hz. When the inclination angle is increased from 0° to 45° every 15° interval, the amplitude of a certain acoustic mode itself decreases, while the amplitudes of the acoustic modes coupled to it basically increase. The acoustic potential energy peaks in the enclosure basically shift to the low frequency with the increase of the inclination angle. Furthermore, the change trend of the acoustic potential energy is regular in the low-order modes, but relatively chaotic in the high-order modes. In addition, in order to verify that the accurate description of the primary sound field is the basis of effective noise control, the two-elastic plate model is deliberately treated as one-elastic plate model, and its influence on the performance of active noise control is discussed. Also, if the multi-elastic plate model is regarded as a simplified automobile cab, the research results can be used for the preliminary acoustic design of the cab; that is, the research results can be used for the acoustic design of similar models.

Understanding the mechanical, thermal, and electrical properties of prismatic lithium-ion batteries (LIBs) is vital to battery safety design, which is key to electric vehicle safety. This study investigated prismatic LIBs subjected to multiple-position indentation loading. The side face of an intact prismatic LIB cell is divided into 15 compressed sections. Experimental results indicate that indentation loading of all sections could initiate thermal runaway. Among the sections studied, that near the positive terminal shows the highest risk of thermal runaway, whereas that near the top-right corner is relatively safe. Failure mode analysis reveals that short circuits may result from contact between the positive and negative current collectors.

Lithium-ion batteries (LIBs) inevitably encounter abusive mechanical loading during engineering applications and result in mechanical deformation, internal short circuit, and even thermal runaway. A 18650 LIB under minor mechanical deformation is subjected to cyclic charge/discharge experiments in this study to analyze its aging behavior. Aging mechanism of the battery with minor deformation is qualitatively investigated through the incremental capacity analysis (ICA). ICA, a commonly used method for exploring degradation mechanism of LIBs, can transform flat voltage plateaus into peaks in the capacity increase curve (IC curve). Experimental data during the battery charging/discharging cycle can be used to calculate the IC curve, which can reflect the characteristics of electrochemical changes inside the battery. Results showed that the LIB suffers from deterioration in the state of health (SOH) in the entire charge/discharge cycle upon minor mechanical deformation. Possible explanations for the slight decrease in SOH with the increasing number of cycles in the early stages and the rapid decrease in the charge/discharge capacity in the late stages were provided. However, precise mechanisms for these phenomena require further detailed research. Moreover, damaged cells demonstrate considerably higher temperature increments than original ones. This temperature difference will increase if additional charging/discharging cycles are conducted. This research infers that additional metallic lithium deposits in damaged cells compared with the original ones cause serious exothermic reactions and lead to enhanced heat accumulation.

Purpose The dent is one of typical surface defects on the surfaces of the machine elements and it is not in fact inerratic. This work aims to investigate the effect of a single dent with a marginal bump on the film shape in elastohydrodynamic lubrication (EHL) point contacts. Design/methodology/approach The experimental investigations of a single dent with marginal bump were carried out using multi-beam interferometry in EHL point contacts. In the meantime, its numerical simulation was also finished using multi-level method and multilevel multi-integration method. The effects of the entrainment velocity and the applied load as well as the slide-roll ratio on the film were chiefly discussed. Meanwhile, the comparison of films between smooth and dented surfaces was conducted under simple sliding conditions. Findings Under pure sliding conditions, the minimum film thickness presents itself near the marginal bump at lower entrainment velocity. The inlet dimple before the marginal bump is subjected to the operating conditions. Under pure rolling conditions, the shape of the dent is almost unchanged when it is passing through the contact region at lower entrainment velocity. The dent depth hardly depends on the applied load under static conditions. However, larger load enhances the inlet dimple and the elastic deformation of the dent with the marginal bump under pure sliding conditions. Originality/value This work is helpful to understanding the effect of the marginal bump before the single dent on point contact EHL films.

The coupled acoustic field of fully elastic plate model is described by the modal analysis method. The acoustic potential energy resonance peaks of the fully elastic plate model are significantly more than that of the one elastic plate model due to the influence of the vibration of multi elastic plates. The acoustic field characteristics of the fully elastic plate model are analyzed when the primary excitation source is applied on the different elastic plates. The results show that the coupled acoustic field of the fully elastic plate model is dominated by the structural mode of the elastic plate with primary excitation, and the acoustic mode of the enclosure, and the structural-acoustic coupling between the plate and the enclosure; the structure modes of the other elastic plates have less effects on the acoustic field in the enclosure except the first ones of them.

Cavitation in fluid film lubrication was experimentally observed by optical interferometry under point and elliptical contacts. Fern leaf cavities and stripe-shaped cavities presented themselves in pure rolling, while string-shaped cavities and sheet cavitation were found in disk simple sliding. Cavitation zone moves downstream toward the outlet of the contact zone with increasing entrainment speed in pure rolling, whereas it is just the reverse in disk simple sliding. Increasing applied load increases threshold speed of occurrence of sheet cavitation. Under elliptical contacts, this threshold speed increases with increasing included angle between the entrainment direction and the minor axis of the elliptical contact zone; the included angle mentioned above markedly affects the position and shape of cavitation zone.

Crankshaft fatigue problem has long been a headache and frequent phenomenon in combustion engine which attracts various efforts especially including fundamental fatigue experimental data. In this paper, the rational experimental method is employed to study the crankshaft fatigue phenomenon based on a customized experiment platform, mimicking the real-world crankshaft working condition physically. Then, based on the experiment data, the statistical regression analysis of eight commonly used hypothesis distributions is conducted. The degrees of fitting effects of the chosen statistical model are evaluated individually. Results show that the three-parameter Weibull distribution model fits the data best which may be used as the fundamental model in future analysis. This study provides a solid foundation for better understanding the mechanism of crankshaft fatigue phenomenon.

In order to understand the dynamics of the tripod sliding universal joint, its dynamic equations were established and then the effects of the joint angle, the rotating radius and mass of the slide rods, the lengths of the input and output shafts and the frequency of the input shaft on its dynamics were investigated. The increase in the mass or rotating radius of the slide rods enhances the amplitudes of all dynamic curves and so does the frequency of the input shaft. Increasing length of the output shaft weakens the amplitudes of the forces and torques at the revolute and spherical pairs as well as the amplitude of the load torque but this length hardly affects the amplitudes of the forces at the tripod arm and the holes of the input shaft. The forces at the holes of the input shaft hardly depend on the joint angle whereas the amplitudes of the remaining dynamic curves increase with the increase of the joint angle. The amplitudes of two torques of the revolute pair increase with increasing length of the input shaft but the remaining forces (torques) are almost independent of its length.

Predicting thermoelastic damping (TED) is crucial in the design of high Q micro-electro-mechanical systems (MEMS) resonators. In the past, some analytical models have been developed for TED in microbeam resonators. Rectangular and circular microplates are also common elements in many micro-resonators. Two analytical models have been developed for TED in the contour-mode vibration and the out-of-plane vibration of circular microplates, respectively. However, there is lack of works that model the TED in the out-of-plane vibration of rectangular microplates. This paper presents an analytical model for the TED in the fully clamped and simply supported rectangular microplates. The quality factor is found by calculating the energy dissipated per cycle of vibration over the volume of the microplate. The derivation in this paper shows that the model for the TED in the fully clamped and simply supported rectangular plates is the same as the model for the TED in the fully clamped and simply supported circular plates. For the rectangular microplates with other boundary conditions, based on Rayleigh's method, this paper presents a set of analytical approximate models to estimate the TED in the rectangular microplates vibrating in the fundamental mode. The present model is validated by comparison with previously reported model and the FEM model.

This paper presents a new approach to the modeling of squeeze-film damping for electrically actuated microbeams under the effect of a static deflection. The approach utilizes the compressible Reynolds equation coupled with the equation governing the beam deflection. Two squeeze-film damping models for a cantilever microbeam and a fixed–fixed microbeam are derived, respectively. The pressure in the air gap is represented by the product of an assumed parabolic function along the beamwidth and a cosine series along the beam length. Compared with the previous models, the present models account for the static deflection due to the electric load; thus the present models can be used for general purpose design, analysis and optimization of microbeam-based devices. The accuracy of the present models is verified by comparing their results with the experimental results available in the literature.

During high speed milling of thin-walled monolithic structure parts, the geometrical and dimensional variability is governed mainly from the choice of process parameters such as operation sequence, selected cutting tool path strategies and the cutting parameters. Therefore, it is necessary to judge the validity of a given process plan before going into actual machining. In this paper, a finite element analysis (FEA) based milling process simulation system was developed to predict machining deformation of aerospace thin-walled monolithic structures. Some key factors such as initial residual stress, cutting loads, cutting sequence and tool path were introduced synthetically into the simulation system. The prediction accuracy of the simulation system was validated experimentally and the obtained numerical and experimental results were found in good agreement.

Predicting squeeze-film damping in rare air is crucial for the design of high-Q MEMS devices. In the past, for MEMS structures with no perforations, there have been two approaches to treating the squeeze-film damping in rare air: using effective viscosity coefficient and using the molecular dynamics method. The amount of squeeze-film damping can be controlled by providing perforations in MEMS structures. To model perforation effects on squeeze-film damping, many methods have been proposed. However, the previous methods are all based on the approach using effective viscosity coefficient. The approaches treat the gas in the gap as a continuum. This paper presents an analytical molecular dynamics model for the squeeze-film damping of a perforated microplate in the free molecular regime. The quality factor is found by calculating the energy transfer from the vibrating plate to the surrounding air due to the collisions between the microplate and the molecules. This paper is an extension of the work done by Bao et al (2002 J. Micromech. Microeng. 12 341–6). Bao's work is valid only for non-perforated microplate. The accuracy of the present molecular dynamics model is verified by comparing its results with the experimental results available in the literature. The limitations of the present molecular dynamics model have been reported in this paper.