The proposed sparsity guided empirical wavelet transform for bearing fault diagnosis: (a) a temporal bearing fault signal; (b) Fourier spectrum of the bearing fault signal; (c) the temporal signal ...reprocessed by autoregressive model; (d) Fourier spectrum of figure (c); (e) identification of Fourier segments by using Steps 1–3 of the sparsity guided wavelet transform; (f) wavelet with Fourier support fl1,fp; (g) Fourier spectrum of the signal filtered by the wavelet in figure (f); (h) squared envelope spectrum of the signal filtered by the wavelet in figure (f); (i) wavelet with Fourier support fp,fh1; (j) Fourier spectrum of the signal filtered by the wavelet in figure (i); (k) squared envelope spectrum of the signal filtered by the wavelet in figure (i); (l) wavelet with Fourier support fh1,fh2; (m) Fourier spectrum of the signal filtered by the wavelet in figure (l); (n) squared envelope spectrum of the signal filtered by the wavelet in figure (l).
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•Sparsity is introduced to guide empirical wavelet transform.•Fourier segments required in empirical wavelet transform are automatically determined.•Several resonant frequency bands are identified for bearing fault diagnosis.•Single and multiple railway axle bearing defects are detected.•Different resonant frequency bands are sensitive to different bearing defects.
Rolling element bearings are widely used in various industrial machines, such as electric motors, generators, pumps, gearboxes, railway axles, turbines, and helicopter transmissions. Fault diagnosis of rolling element bearings is beneficial to preventing any unexpected accident and reducing economic loss. In the past years, many bearing fault detection methods have been developed. Recently, a new adaptive signal processing method called empirical wavelet transform attracts much attention from readers and engineers and its applications to bearing fault diagnosis have been reported. The main problem of empirical wavelet transform is that Fourier segments required in empirical wavelet transform are strongly dependent on the local maxima of the amplitudes of the Fourier spectrum of a signal, which connotes that Fourier segments are not always reliable and effective if the Fourier spectrum of the signal is complicated and overwhelmed by heavy noises and other strong vibration components. In this paper, sparsity guided empirical wavelet transform is proposed to automatically establish Fourier segments required in empirical wavelet transform for fault diagnosis of rolling element bearings. Industrial bearing fault signals caused by single and multiple railway axle bearing defects are used to verify the effectiveness of the proposed sparsity guided empirical wavelet transform. Results show that the proposed method can automatically discover Fourier segments required in empirical wavelet transform and reveal single and multiple railway axle bearing defects. Besides, some comparisons with three popular signal processing methods including ensemble empirical mode decomposition, the fast kurtogram and the fast spectral correlation are conducted to highlight the superiority of the proposed method.
Many mechanical systems including rolling/sliding parts, require traction data across a spectrum of operating conditions to predict their motion effectively. Numerous studies have examined the ...thermal effects and shear-thinning concerning the traction curve, but only a few have focused on the traction coefficient in the linear isothermal regime for low SRR. In this work, we investigate traction coefficient characteristics of EHL point contacts in the linear isothermal regime, over a wide range of operational conditions. To this end, we conduct numerical simulations utilizing a fully-coupled finite element-based model, resulting in a prediction formula for the traction coefficient slope. With this formula, the traction coefficient slope could be predicted for the operating conditions considered.
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Many mechanical products including rolling/sliding parts are used with various lubricants and operating conditions. Increasing the efficiency and reliability of products requires an essential ...understanding of the traction characteristics of the rolling/sliding parts. Many researchers have investigated the traction characteristics of rolling/sliding EHL contacts considering shear-thinning, thermal effects, and roller compliance. There are, however, only a few papers concerning the modeling of traction characteristics in the linear isothermal region at low slide-to-roll ratios. We propose a prediction formula for the dimensionless traction coefficient for EHL line contacts in the linear isothermal region. The formula was obtained by numerical simulations using a fully-coupled finite-element EHL line contact solver, and it is applicable for the piezoviscous rigid/elastic, and the isoviscous rigid/elastic regimes.
Ionic liquids (ILs) attract high interest as lubricants or lubricant additives due to their special physicochemical characteristics. CO 2 is a widely distributed gas. In many situations, its ...influence on lubricants cannot be avoided. In this work, three ILs are synthesized from choline and amino acids of glycine, l-proline and lysine, respectively. The influence of CO 2 absorption on their solubility and lubricity is investigated. In general, it is interesting to find that the solubility is decreased and their lubricity is obviously improved after absorbing CO 2 , which is strongly related to their functional group (amino group) interactions with CO 2 . The formation of carbamate groups greatly increases the viscosity resulting in less solid contacts, and strengthens the interfacial adhesion between ILs and solids.
Many high temperature (HT) forming processes require the use of solid lubricants in order to control friction and reduce wear. In an attempt to eliminate the need for solid lubrication in high ...temperature sliding applications, nickel-based self-lubricating coatings with the addition of Ag and MoS 2 were prepared by means of laser cladding on stainless steel substrates.
The behaviour of the resulting laser claddings was thoroughly evaluated up to 600 °C, including the oxidation behaviour and reciprocating tribotesting using different counter body geometries (ball and flat pin). The self-lubricating coatings showed lower friction than the unmodified reference alloy at all tested temperatures, in addition to a significant microstructural stability after prolonged exposure at high temperatures. The addition of solid lubricants to the claddings was also found to be beneficial in terms of the counter body wear at HT, as no material loss could be measured for the bearing balls after testing at 600 °C against the self-lubricating claddings, despite the significant softening experienced by AISI 52100 bearing steel at HT.
