Tribological behaviors of vacuum hot-pressed ceramic composites with enhanced cyclic oxidation and corrosion resistance

Wear failure is a bottleneck restricting applications and developments of Ti3SiC2 ceramic. Particles reinforced composites provide an effective strategy to resist wear. In this work, Ti(C,N) particles are used as reinforcements, and Ti3SiC2/Ti(C,N) composite is fabricated by vacuum hot-pressing. Scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and X-ray diffract meter (XRD) are used to investigate composite morphologies, compositions and phases before and after hot-pressing. Meanwhile, high-temperature cyclic oxidations and tribological behaviors of composites under various loads, speeds and Ti(C,N) contents are characterized. Results show that as-prepared composite is relatively dense, and Ti(C,N) addition plays an important role in particle reinforcement of Ti3SiC2. Meanwhile, its hardness, wear resistance, cyclic oxidation resistance and corrosion resistance are significantly improved. In addition, wear characteristics and mechanisms of composites under different loads and speeds are analyzed in details. This work shows great potentials in developing engineering applications of ceramics, especially in high-temperature, oxidizing, frictional and corrosive environment

Improving the Corrosion Resistance of Aluminum Alloy by Creating a Superhydrophobic Surface Structure through a Two-Step Process of Etching Followed by Polymer Modification

A multifunctional aviation aluminum alloy with good superhydrophobicity and corrosion resistance was prepared by a two-step process of etching followed by polymer modification. Meanwhile, micro- and nanostructures formed on the processed sample. Compared with bare sample, the static liquid contact angle on the as-prepared sample was increased by 100.8°. Further polarization tests showed that the corrosion potential of such a sample increased, and the corrosion current density decreased obviously, thus suggesting that the corrosion resistance of the modified sample was significantly improved. The same conclusion was confirmed by subsequent impedance testing. The work is of great economic value and practical significance to enhance the corrosion resistance of aviation actuator materials and also lays a foundation for future hydrophobic application research in aeronautical engineering

Modification of Pectin and Hemicellulose Polysaccharides in Relation to Aril Breakdown of Harvested Longan Fruit

To investigate the modification of cell wall polysaccharides in relation to aril breakdown in harvested longan fruit, three pectin fractions (WSP, water soluble pectin; CSP, CDTA-soluble pectin; ASP, alkali soluble pectin) and one hemicellulose fraction (4 M KOH-SHC, 4 M KOH-soluble hemicellulose) were extracted, and their contents, monosaccharide compositions and molecular weights were evaluated. As aril breakdown intensified, CSP content increased while ASP and 4 M KOH-SHC contents decreased, suggesting the solubilization and conversion of cell wall components. Furthermore, the molar percentage of arabinose (Ara), as the main component of the side-chains, decreased largely in CSP and ASP while that of rhamnose (Rha), as branch point for the attachment of neutral sugar side chains, increased during aril breakdown. Analysis of (Ara + Gal)/Rha ratio showed that the depolymerization of CSP and ASP happened predominantly in side-chains formed of Ara residues. For 4 M KOH-SHC, more backbones were depolymerized during aril breakdown. Moreover, it was found that the molecular weights of CSP, ASP and 4 M KOH-SHC polysaccharides tended to decrease as aril breakdown intensified. These results suggest that both enhanced depolymerization and structural modifications of polysaccharides in the CSP, ASP and 4 M KOH-SHC fractions might be responsible for aril breakdown of harvested longan fruit

Hierarchical Lateral Control Scheme for Autonomous Vehicle with Uneven Time Delays Induced by Vision Sensors

Vision-based sensors are widely used in lateral control of autonomous vehicles, but the large computational cost of the visual algorithms often induces uneven time delays. In this paper, a hierarchical vision-based lateral control scheme is proposed, where the upper controller is designed by robust H∞-based linear quadratic regulator (LQR) algorithm to compensate sensor-induced delays, and the lower controller is based on logic threshold method, in order to achieve strong convergence of the steering angle. Firstly, the vehicle lateral model is built, and the nonlinear uncertainties induced by time delays are linearized with Taylor expansion. Secondly, the state space of the system is augmented to describe such uncertainties with polytopic inclusions, which is controlled by an H∞-based LQR controller with a low cost of online computation. Then, a lower controller is designed for the control of the steering motor. According to the results of the vehicle experiment as well as the hardware-in-the-loop (HIL) experiment, the proposed control scheme shows good performance in vehicle’s lateral control task, and exhibits better robustness compared with a conventional LQR controller. The proposed control scheme provides a feasible solution for the lateral control of autonomous driving

Development of grid-reinforced carbon fiber mirrors using high-precision optical replication technology

<p>Due to low density, high specific stiffness, and low thermal expansion, carbon fiber reinforced plastic (CFRP) is believed to be one of the potential material choices for optical mirrors. But CFRP is one of the two-phase materials that cannot be used as optical surface and must be surface modified. To develop one kind of grid-reinforced CFRP mirror, optical replication technology was used to modify and achieve high-precision surface, and theoretical deformation due to replica resin curing and deformation caused by laminates&#39; manufacturing errors were studied in detail. Optical replication experiment has shown that &lambda; / 20 root mean square high-precision surface can be achieved for &phi;100-mm grid-reinforced carbon fiber mirrors. &copy; 2018 Society of Photo-Optical Instrumentation Engineers (SPIE).</p