Study on microstructure and properties of AA7075 coated by micro arc oxidation

Effect of ageing temperature on the properties of 7075 aluminum alloy coated by micro arc oxidation (MAO) technology has been investigated. The precipitates formed at various ageing temperatures are observed by transmission electron microscope (TEM), which would significantly influence the properties of the MAO coating. Coherent distortion, size and volume fraction of precipitates are related to the changing of electrical conductivity during ageing treatment. Full coherent and dense Guinier Preston zones (GP zones) formed at 90 °C can act as scattering centers to impede electron mobility, so decrease the electrical conductivity. η and η′ phases produced at 120 °C and 150 °C are semi-coherent and incoherent, respectively, meanwhile, the precipitate size increases and the volume fraction decreases with increasing the ageing temperature, therefore, the electrical conductivity increases. Higher electrical conductivity contributes to thicker coating with better surface morphology. Double cantilever beam (DCB) tests show that the thicker and less porous coatings prepared at 150 °C aged specimens own the best stress corrosion cracking (SCC) resistance. After pores are broke and coatings are ruptured, high Cu and low Mg segregation at the grain boundary of 150 °C aged specimens founded from high-angle annular dark field scanning transmission electron microscopy (HADDF-STEM) are beneficial to anodic dissolution and hydrogen assisted crack

Research on Predicting Remain Useful Life of Rolling Bearing Based on Parallel Deep Residual Network

The prediction of bearing remaining useful life (RUL) plays a pivotal role in ensuring the safe operation of machinery and reducing maintenance loss. Traditional prediction methods only consider the features of one domain or integrate the features of multiple domains into a one-dimensional sequence as the model input, which leads to some inaccuracy in prediction. In order to improve the prediction accuracy, a bearing RUL prediction method based on the parallel deep residual convolution neural network (P-ResNet), which is considered both time-domain features and time–frequency features, is proposed in this paper. Synchronous wavelet transform (SWT) is adopted to extract time–frequency features from original vibration signals. Both the time domain features and time–frequency domain features after dimension reduction by PCA are used as input to P-ResNet, which contains two series of parallel convolution operations to learn the time–frequency features and time-domain features, respectively, to ensure the comprehensiveness of information-bearing degradation. The residual layers were added to enhance the learning ability of time–frequency features. Kalman filter algorithm was used to smooth the prediction results. The IEEE PHM 2012 Data Challenge datasets were used as data sources for model training and prediction. Compared with the traditional convolutional neural network (CNN), the P-ResNet model maintains the synchronization of global and local information and has a stronger learning ability. The experiment data validate the effectiveness of the proposed method, and the comparison between the prosed methods and the others proves the superiority of the proposed method

Effect of ultrasound with methylene blue as sound sensitive agent on virus inactivation

The goal of this paper is to explore a method for virus inactivation based on ultrasonic treatment, and on this basis, to explore the synergistic effect of methylene blue as a sonosensitizer in virus inactivation. The titer of human parainfluenza virus type 3 (HPIV3), Autographacaliforinica nuclear polyhedrosis virus carried a green fluorescent reporter gene (AcNPV-GFP) and Enterovirus group D 68 (EV-D68) were determined by plaque assays or TCID50 methods after treatment by MB combined with illumination (MB photochemical, MBP) or ultrasonic excitation. Different ultrasonic power and time, MB concentration gradient were set to determine the best anti-viral combination. For the enveloped virus HPIV3 and AcNPV-GFP, pure ultrasonic or MBP treatment could reduce viral titer more than 104，and ultrasonic combined with MB could completely inactivate HPIV3 and AcNPV-GFP in 5min while traditional MBP methods could only reduce viral titer about 10X. For the non-enveloped virus EV-D68, pure ultrasonic or MBP treatment only reduced the viral titer about 102, but ultrasonic combined with MB treatment could reduce the viral titer about 103 in 5min and completely inactive EV-D68 in 10min (reduced 105). Compared with MBP method and pure ultrasonic inactivation, ultrasonic combined with MB has better inactivation effect on either enveloped or non-enveloped viruses, and the appropriate combination of parameters is expected to be a new blood transfusion transmitted virus inactivation method