Wavelets’ filters and higher-order frequency analysis of acoustic emission signals from termite activity

A comparative analysis between two higher-order statistics in the frequency domain, combined with wavelets’ filters, confirms the existence of three frequency sub-bands that characterize the species emission. De-noising via wavelet eliminates the symmetrical noise and reveals non-Gaussian features. Here, we show that the spectral kurtosis enhances the low and high-frequency components with high power variability, once the filter banks are applied, revealing new zones in the spectrum that are associated to high variability in the amplitudes. Despite de-noising via wavelets, the bi-spectrum is attenuated, but it confirms the frequency pattern of the emission, denoting at the same time the non-zero skewness of these components. Complementarily, it is observed that high bi-frequencies are attenuated more severely, suggesting the idea that certain frequencies content more information regarding symmetry than others. Results have been confirmed using three common wavelet families.     

Hydrogen degradation of steel 12X1MΦ and its estimation by the acoustic emission method

The acoustic emission method for estimating damage to specimens made of thermally resistant steel is described as applied in air and in a gaseous hydrogen medium. Acoustic diagrams (AD) of steel cracking and their interpretation are presented. It is shown that thermal cycling of the steel in air and in a hydrogen medium leads to an increase in bulk damage to the steel. It is shown that the exploited material is more subject to micro- and macrocracking under the influence of temperature and the working environment.     

Bayesian Analysis on Deming’s Model with Consideration of Inspection Errors

This paper studies an extension to Deming’s model for inspection sampling. This new model is more useful in practice since it takes into account the two inspection errors (i.e. accepting out of tolerance components or rejecting in tolerance components) with the goal of minimising the expected total cost. Mathematical formulae corresponding to the model are derived based on the Bayesian approach. A computer program of this model is available for industry. Some numerical analysis of the effects due to model factors, such as inspection errors, component quality, and k₂ /k₁ ratio, is also presented. As a result, we conclude that a model that involves the two types of inspection error will lead to a looser inspection policy and higher expected total cost than a model without inspection errors. This method can be used to select the best suppliers when the total cost of the product is the main concern of the producer. ID="A1" Correspondence and offprint requests to: Dr C.-C. Chyu, Department of Industrial Engineering and Management, Yuan-Ze University, Chung-Li, Taiwan 320. E-mail: iehshsu@saturn.yzu.edu.tw     

Machine of testing the ceramic’s bending strength properties at high temperature and ultra-low speed

According to the established rules for testing ceramic’s bending strength, the falling velocity of the pressure head of the machine should be more than 0.5 mm/min. For the machine of testing the ceramic’s bending strength properties, most designs adopt the lowest falling velocity as 0.5 mm/min. In the fields such as aerospace and deep-ocean exploration, the utilization of ceramic materials that work at normal temperature, low temperature, or even high temperature and bend at an ultra-low velocity is increasing; thus, the intense requirements for the machine of testing the ceramic’s bending strength properties at high temperature and ultra-low speed (MTCBSP) and its experimental basis are put forward. This research developed an MTCBSP suitable for normal temperature and high temperature with the lowest falling velocity of 0.05 mm/min, and manufactured a drive reducer for ultra-low speed and high-temperature working condition. In the test, equipment includes a high-temperature furnace, bending die for four-point bending, and protection system of inert gas, which was placed in the high-temperature furnace to prevent the ceramic sample from being oxidized to diminish its effects. The results show that the lowest falling velocity of the pressure head of this new machine is 0.05 mm/min, and the mechanical properties of silica glasses are noticeably different at the same high temperature and the different falling velocities of 0.5 mm/min and 0.05 mm/min.     

Measurement and evaluation of the apparent modulus of elasticity of apple based on Hooke’s,Hertz’s and Boussinesq’s theories

Awareness on the mechanical properties of agricultural products is necessary in order to estimate and predict the deformation of viscoelastic materials under external loads for system design, transport, processing and packaging. The aim of this study was to evaluate three theories (i.e. Hooke, Hertz and Boussinesq) on the apparent modulus of elasticity of some apple varieties i.e. Golden Delicious, Red Delicious and Granny Smith. The theoretical results were analyzed in a factorial experiment with completely randomized design with 9 treatments and 15 replicates. The results showed the practical usability of Hertz’s theory with better prediction accuracy whilst the Boussinesq’s theory showed a significant difference of predicted modulus of elasticity compared to other theories and the values reported in some publications. Although, the Hook’s theory enables the identification of a bio-yield point on its force–deformation curve, but Hertz’s theory was recommended as the most appropriate method due to easiness of working on a cylindrical sample of apple and the closer agreement with reality. Based on the results of this study, Golden Delicious and Granny Smith varieties had the lowest and the highest modulus of elasticity as 2.211 MPa and 3.431 MPa, respectively. This difference shows the firmness of apple varieties and different tissue responses to external loads and forces accordingly.     

Baushinger’s Effect in Wear of Materials

The response of Cu–40%Zn alloy to wear during unidirectional and bidirectional abrasion processes was investigated. It was observed that the mass loss of the alloy decreased as the number of times of changing the sliding direction was increased. Corresponding to this decrease in mass loss, hardness of the worn surface increased initially and then decreased. Cracking in the surface layer was analyzed to get an insight into the mechanism involved. Results of the study suggest that Baushinger’s effect played a role when the sliding direction was alternated.     

Overview of Rubik’s Cube and Reflections on Its Application in Mechanism

Rubik’s Cube is a widely popular mechanical puzzle that has attracted attention around the world because of its unique characteristics. As a classic brain-training toy well known to the public, Rubik’s Cube was used for scientific research and technology development by many scholars. This paper provides a basic understanding of the Rubik’s Cube and shows its mechanical art from the aspects of origin and development, characteristics, research status and especially its mechanical engineering design, as well as making a vision for the application in mechanism. First, the invention and origin of Rubik’s Cube are presented, and then the special characteristics of the cube itself are analyzed. After that, the present researches of Rubik’s Cube are reviewed in various disciplines at home and abroad, including the researches of Rubik’s Cube scientific metaphors, reduction algorithms, characteristic applications, and mechanism issues. Finally, the applications and prospects of Rubik’s Cube in the field of mechanism are discussed.     

A new modeling and compensation approach for creep and hysteretic loops in nanosteering by SPM’s piezotubes

This paper aims to investigate how the recent overheating economy and other economic factors influence the manufacturing industry in China. It makes use of Chinese historical data from 1950 to 2007 provided in the China Statistical Databases authorized by the National Bureau of Statistics of China for the development of econometric models. Regression analysis is used to investigate and verify the importance of and relationships among the variables, while exponential smoothing and autoregressive integrated moving average methods are applied for forecasting the important variables. This study provides empirical evidence to identify the main impact factors on the growth of the manufacturing industry, thereby enabling firms to take them into account when planning their manufacturing strategy. It also enables firms to get an insight into the development of China’s manufacturing industry in this dynamic, competitive economy.     

Modeling of fatigue crack growth closure considering the integrative effect of cyclic stress ratio, specimen thickness and Poisson’s ratio

Key components of large structures in aeronautics industry are required to be made light and have long enough fatigue lives.It is of vital importance to estimate the fatigue life of these structures accurately.Since the FCG process is affected by various factors,no universal model exists due to the complexity of the mechanisms.Most of the existing models are obtained by fitting the experimental data and could hardly describe the integrative effect of most existing factors simultaneously.In order to account for the integrative effect of specimen parameters,material property and loading conditions on FCG process,a new model named integrative influence factor model(IIF) is proposed based on the plasticity-induced crack closure theory.Accordingly to the predictions of crack opening ratio(γ) and effective stress intensity factor range ratio(U) with different material under various loading conditions,predictions of γ and U by the IIF model are completely identical to the theoretical results from the plane stress state to the plane strain state when Poisson’s ratio equals 1/3.When Poisson’s ratio equals 0.3,predictions of γ and U by the IIF model are larger than the predictions by the existing model,and more close to the theoretical results.In addition,it describes the influence of R ratios on γ and U effectively in the whole region from-1.0 to 1.0.Moreover,several sets of test data of FCG rates in 5 kinds of aluminum alloys with various specimen thicknesses under different loading conditions are used to validate the IIF model,most of the test data are situated on the predicted curves or between the two curves that represent the specimen with different thicknesses under the same stress ratio.Some of the test data slightly departure from the predictions by the IIF model due to the surface roughness and errors in measurement.Besides,based on the analysis of the physical rule of crack opening ratios,a relative thickness of specimen is defined to describe the influence of material property,specimen thickness and so forth on FCG characteristics conveniently.In conclusion,the relative thickness of specimen simplifies the expression of FCG characteristic and provides a general parameter to analyze the fatigue characteristics of different materials with various thicknesses under different loading conditions.The IIF model describes the integrative effect of existing influence factors explicitly and quantitatively,and provides a helpful tool for fatigue property estimation of practical component and experiment design.     

The prediction technology study of fatigue life for key parts of a tracked vehicle’s suspension system

In allusion to fatigue life of a tracked vehicle torsion bar, a virtual prototype model of the tracked vehicle suspension system including a flexible torsion bar was built based on dynamic simulation software ADAMS. Node force and stress results of the torsion bar from last step simulation were acquired; taking into account the material characteristics and influential factors, fatigue life of the flexible body of the torsion bar was predicted. Engineering results can be acquired through the contrast of the result of virtual test and statistical fatigue.     

Control of load’s speed of ascent in crane operation

The proposed control system for the load??s speed of ascent in crane operation ensures smooth startup by means solely of mechanical components.     

Assessing the quality of inspection for tapered aircraft fastener holes using an engineer’s blue contact test

Tapered interference-fit fasteners (e.g. Taper-lok) are commonly used by the aerospace industry due to their high fatigue strength. The inspection relies on a ‘true’ geometry gauge coated with a thin film of engineer’s blue being brought firmly into contact with the tapered hole. The pattern created on the gauge is then used to identify bearing surface area and distribution. This research investigates if the inspection reflects the hole geometry, and under what conditions the inspection may be assumed valid. The results show that the shade of the blue on the gauge as inspected through computer vision correlates with the unloaded geometry evaluated via a roundness tester, in particular when the red channel is taken alone. The inspection method falls short of accurately representing small features, particularly those tangential to the gauge removal direction. Thresholding visually or by computer vision may reasonably be used to identify the contact region pattern, however factors limiting blue migration mean the contact area may appear smaller than it actually is.     

Reconstruction of emission coefficients for a non-axisymmetric coupling arc based on MALDONADO’s method

The reconstruction of emission coefficient is a key factor for the calculation of temperature field.However,most of the researches for determining arc plasmas are based on axisymmetric sources,little has been done to study non-axisymmetric arc plasmas.In order to reveal temperatures of a non-axisymmetric coupling arc,the distribution of emission coefficients must be reconstructed in advance.In this paper,the argon atomic line intensities of the coupling arc are obtained by using the imaging system that involves a high speed camera in conjunction with a neutral and a narrow-band filter.The converted programme between emission coefficients and emitted intensities is programmed based on MALDONADO’s method.A displaced Gaussian model is used for evaluating the validity of the converted programme.Then,the emission coefficients of a free burning arc are reconstructed by MALDONADO’s method and an Abel inversion,respectively,and good agreement is obtained.Finally,the emission coefficient profiles of the coupling arc are achieved.The results show that the distribution of emission coefficient for the coupling arc is non-axisymmetric.The emission coefficient profile is similar to an ellipse,and the short axis of the ellipse is in the direction that the two electrodes are arranged along.The peak temperature of the coupling arc is in the middle of both electrodes.There is a strong interaction between both arcs within the coupling arc.The proposed research solves difficulties for determining asymmetric arcs and enlarges the application scope of spectroscopic techniques.     

A two stroke free piston engine’s performance and exhaust emission using artificial neural networks

Journal of Mechanical Science and Technology - The performance and exhaust emissions of a Free piston linear engine (FPLE) were ascertained for various equivalence ratios (0.7, 0.8, 0.9, 1.0, 1.1...     

Rate of the tribooxidative and diffusional wear of a tool’s contact surfaces in the machining of metals

The tribooxidative and diffusional fluxes of tool material into the blank are compared. This permits the identification of the dominant type of wear in machining, for different technological conditions.     

Static and dynamic pull-in instability of multi-walled carbon nanotube probes by He’s iteration perturbation method

A continuum model is utilized to extract the nonlinear governing equation for Carbon nanotube (CNT) probes near graphite sheets. The van der Waals (vdW) intermolecular force and electrostatic actuation are included in the equation of motion. Static and dynamic pull-in behavior of the system is investigated in this paper. To this end, a new asymptotic procedure is presented to predict the pull-in instability of electrically actuated CNTs by employing an analytic approach namely He’s iteration perturbation method (IPM). The effects of basic non-dimensional parameters such as initial amplitude, intermolecular force, geometrical parameter and actuation voltage on the pull-in instability as well as the fundamental frequency are studied. The obtained results from numerical simulations by employing three mode assumptions verify the strength of the analytical procedure. The qualitative analysis of the system dynamics shows that the equilibrium points of the autonomous system include stable center points and unstable saddle nodes. The phase portraits of the carbon nanotube actuator exhibit periodic and homoclinic orbits.     

Surface roughness and roundness of bearing raceway machined by floating abrasive polishing and their effects on bearing’s running noise

As the two most important indexes of bearing raceway, surface roughness and roundness have significant influence on bearing noise. Some researchers have carried out studies in this field, however, reason and extent of the influence of raceway surface geometric characteristics on bearing running noise are not perfectly clear up to now. In this paper, the raceway of 6309 type bearing＇s inner and outer ring is machined by floating abrasive polishing adopting soft abrasive pad. Surface roughness parameters, arithmetical mean deviation of the profile Ra, the point height of irregularities Rz, maximum height of the profile Rmax and roundness fof raceways, are measured before and after machining, and the change rules of the measured results are studied. The study results show that the floating abrasive polishing can reduce the surface geometric errors of bearing raceway evidently. The roundness error is reduced by 25%, Rm~x value is reduced by 35.5%, Rz value is reduced by 22% and Ra value is reduced by 5%. By analyzing the change of the geometrical parameters and the shape difference of the raceway before and after machining, it is found that the floating abrasive polishing method can affect the roundness error mainly by modifying the local deviation of the raceway＇s surface profile. Bearings with different raceway surface geometrical parameter value are assembled and the running noise is tested. The test results show that Ra has a little, Rmax and Rz have a measurable, and the roundness error has a significant influence on the running noise. From the viewpoint of controlling bearings＇ running noise, raceway roundness error should be strictly controlled, and for the surface roughness parameters, R,n~x and Rz should be mainly controlled. This paper proposes an effective method to obtain the low noise bearing by machining the raceway with floating abrasive polishing after super finishing.     

Dynamics and Wheel’s Slip Ratio of a Wheel-legged Robot in Wheeled Motion Considering the Change of Height

The existing research on dynamics and slip ratio of wheeled mobile robot (WMR) are derived without considering the effect of height, and the existing models can not be used to analyze the dynamics performance of the robot with variable height while moving such as NOROS-Ⅱ. The existing method of dynamics modeling is improved by adding the constraint equation between perpendicular displacement of body and horizontal displacement of wheel into the constraint conditions. The dynamic model of NOROS-Ⅱ in wheel motion is built by the Lagrange method under nonholonomic constraints. The inverse dynamics is calculated in three different paths based on this model, and the results demonstrate that torques of hip pitching joints are inversely proportional to the height of robot. The relative error of calculated torques is less than 2% compared with that of ADAMS simulation, by which the validity of dynamic model is verified. Moreover, the relative horizontal motion between fore?hind wheels and body is produced when the height is changed, and thus the accurate slip ratio can not be obtained by the traditional equation. The improved slip ratio equations with the parameter of the vertical velocity of body are introduced for fore wheels and hind wheels respectively. Numerical simulations of slip ratios are conducted to reveal the effect of varied height on slip ratios of different wheels. The result shows that the slip ratios of fore?hind wheels become larger?smaller respectively as the height increases, and as the height is reduced, the reverse applies. The proposed research of dynamic model and slip ratio based on the robot height provides the effective method to analyze the dynamics of WMRs with varying height.     

System and prospects of China’s intercity rail transit technology

City clusters and metropolitan areas in China are flourishing in the midst of the deepening urbanization in the country, thereby resulting in the emergence of intercity rail transit. Intercity railways connect mainline and urban railways for an integrated regional transportation system that underpins and leads the development of city clusters and metropolitan areas. This study explores the development mode and service characteristics of intercity rail transit, as well as proposes overviews on this system and prospects of its future technology in China.