Conventional classification of hand motions and continuous joint angle estimation based on sEMG have been widely studied in recent years. The classification task focuses on discrete motion ...recognition and shows poor real-time performance, while continuous joint angle estimation evaluates the real-time joint angles by the continuity of the limb. Few researchers have investigated continuous hand action prediction based on hand motion continuity. In our study, we propose the key state transition as a condition for continuous hand action prediction and simulate the prediction process using a sliding window with long-term memory. Firstly, the key state modeled by GMM-HMMs is set as the condition. Then, the sliding window is used to dynamically look for the key state transition. The prediction results are given while finding the key state transition. To extend continuous multigesture action prediction, we use model pruning to improve reusability. Eight subjects participated in the experiment, and the results show that the average accuracy of continuous two-hand actions is 97% with a 70 ms time delay, which is better than LSTM (94.15%, 308 ms) and GRU (93.83%, 300 ms). In supplementary experiments with continuous four-hand actions, over 85% prediction accuracy is achieved with an average time delay of 90 ms.
Duplex stainless steel was formed through welding wire and arc additive manufacturing (WAAM) using tungsten inert gas. The effects of wire feeding speed (WFS), welding speed (WS), welding current, ...and their interaction on the weld bead width and height were discussed. Back-propagation (BP) neural network algorithm prediction model was established by taking the bead width and height as the output layer, and the network weight and threshold values were optimized using the particle swarm optimization (PSO) algorithm to obtain the prediction model of bead width and height. The predicted results were verified by experiments. Results show that the weld bead width increases with the increase in WFS and the welding current and decreases with WS. The smaller the WFS, the faster the WS, which is beneficial for the generation of equiaxed crystals. The smaller the welding current, the faster the cooling speed of the metal melt, which is conducive to the formation of dendrites. The interaction among WS, wire feed speed, and welding current has a significant effect on the bead width. The weld bead height is positively correlated with the wire feed speed and negatively correlated with the WS and current. The interaction between the wire feed speed and WS is significant. The optimized WAAM process parameters for duplex stainless steel are a wire feed speed of 200 cm/min, WS of 24 cm/min, and welding current of 160 A. The maximum error of the BP neural network in predicting the weld bead width and height is 7.74%, and the maximum error between the predicted and experimental values of the BP-PSO neural network is 4.27%. This finding indicates that the convergence speed is fast, improving the prediction accuracy.
The water-meter shell has a complex-structured thin-walled cavity, and it can cause casting defects such as shrinkage and misrun. On the basis of structural analysis of a water-meter shell, a ...three-dimensional model and a finite element model of the water-meter shell were constructed using the SOLIDWORKS and ProCAST software as a modeling tool and a casting numerical simulation tool, respectively. Three processes associated with the bottom gating system without a riser, a step gating system with a preliminary riser, and a step gating system with an optimum riser were successively numerically simulated. The mold-filling sequence, temperature distribution, liquid-phase distribution during solidification, and shrinkage distribution of these three processes are discussed here. The numerical simulation results indicated that optimization of the casting process and the rational assembling of the riser led to the shrinkage volumes at the inlet position, regulating sleeve, and sealing ring of the water-meter shell decreasing from 0.68 to 0 cm3, 1.39 to 0.22 cm3, and 1.32 to 0.23 cm3, respectively. A comparison between model predictions and experimental measurements indicated that the castings produced by the optimized process had good surface quality and beautiful appearance, without casting defects, demonstrating that numerical simulation can be used as an effective tool for improving casting quality.
Laser cladding is a new surface repair method that can improve the wear and corrosion resistance of substrate surfaces. However, the cladding layer typically exhibits a rough surface, high hardness ...and large residual tensile stress, and thus requires further machining and finishing. Ultrasonic rolling (U-rolling) is a highly efficient finishing and strengthening process that combines ultrasonic technology with traditional rolling (T-rolling). In this study, an iron-based alloy was coated onto the surface of H13 die steel using laser cladding, and the surface of the cladding layer was polished using U-rolling. The effects of U-rolling on the surface quality, corrosion resistance and friction and wear properties of the laser-cladding layer were investigated and compared with those obtained by T-rolling. The surface roughness of the U-rolled sample was only 1/4 that of the T-rolled sample. The hardness and residual compressive stress of the laser cladding layer after U-rolling were higher than those after T-rolling. Similarly, the surface corrosion resistance of the laser cladding layer after U-rolling was higher than that after T-rolling. U-rolling changed the surface roughness, grain size, and residual stress of the material and thus affected the corrosion resistance of the laser cladding layer. The friction coefficient and wear rate of the U-rolled surface of the cladding layer were lower than those of the T-rolled surface. In addition, the tribological properties of the cladding layer were found to be related to the rolling direction. When the friction direction of the sample was the same as the rolling direction, its friction and wear performance were higher than those when the two directions were perpendicular.
Copper particles emitted from braking have become a significant source of environmental pollution. However, copper plays a crucial role in resin-based braking materials. Developing high-performance ...braking materials without copper has become a significant challenge. In this paper, the resin-based braking materials were filled with fly-ash cenospheres to develop copper-free braking materials. The effects of fly-ash cenospheres on the physical properties, mechanical and friction and wear properties of braking materials were studied. Furthermore, the wear mechanism of copper-free resin-based braking materials filled with fly-ash cenospheres was discussed. The results indicate that the inclusion of fly-ash cenospheres in the braking materials improved their thermal stability, hardness and impact strength, reduced their density, effectively increased the friction coefficient at medium and high temperatures, and enhanced the heat-fade resistance of the braking materials. The inclusion of fly-ash cenospheres contributed to the formation of surface friction film during the friction process of the braking materials, and facilitated the transition of form from abrasive wear to adhesive wear. At 100–350 ℃, the friction coefficient of the optimal formulation is in the range of 0.57–0.61, and the wear rate is in the range (0.29–0.65) × 10
−7
cm
3
·N
−1
·m
−1
, demonstrating excellent resistance to heat-fade and stability in friction coefficient. This research proposes the use of fly-ash cenospheres as a substitute for environmentally harmful and expensive copper in brake materials, which not only improves the performance of braking materials but also reduces their costs.
The main focus of current research in polymeric matrix brake composites is on searching out a replacement for copper, which has been recently proved to be a hazard to human health and the ...environment. In this paper, rare earth lanthanum oxide was explored for the replacement of copper in composites. The mechanism of the role of lanthanum oxide in brake composites to replace copper was analyzed. Four series of polymeric matrix brake composites with various amounts of copper (15, 10, 5 and 0 wt %) and rare earth lanthanum oxide (0, 5, 10 and 15 wt %) were developed, in which the copper was gradually replaced by lanthanum oxide in the formula. These series were characterized in terms of physical, thermo-physical and mechanical properties. The results show that lanthanum oxide can be successfully used as a replacement for copper in brake composites. Brake composites with 15 wt % lanthanum oxide that are copper-free are considered optimal, where tribo-properties are considered best. Compared with the addition of copper in brake composites, lanthanum oxide is more conducive to the formation of compacted friction films and transfer films, which is beneficial to the tribological properties of the brake composites. The addition of La₂O₃ to the brake composites can cause the reaction between La₂O₃ and Al₂O₃ to form LaAlO₃, and the reaction between Al₂O₃ and BaSO₄ can produce Ba
Al
O
and Al₂SO₄ during the friction and wear processes, which can effectively improve the tribological properties of the brake composites at elevated temperature. This research was contributive to the copper-free, metal-free and eco-friendly brake composites.
In this study, NSSC 2120 economical duplex stainless steel was prepared and the effects of aging temperatures on its intermetallic phase morphology, tensile strength, elongation, corrosion ...resistance, and antimicrobial properties were investigated. The results revealed that after aging the sample at 650 °C, it exhibits better pitting corrosion resistance and higher tensile strength. Upon increasing the aging temperature up to 750 °C, the pitting corrosion resistance and tensile strength of the samples were decreased due to the precipitation of the ε-Cu phase in the matrix. Moreover, with the further increase in the aging temperature to 850 °C, oxides containing Mn and Cr (CrMn
O
) and sulfides (MnS) precipitated from the samples, further decreasing their pitting corrosion resistance and tensile strength. Upon aging the samples at 950 °C, no second phase was observed and the corrosion resistance was less than that of the sample after aging at 650 °C, but the tensile strength was greater than that of the sample after aging at 650 °C. Antibacterial test results revealed that the sample after aging at 750 °C exhibited a good antibacterial effect due to the precipitation of the rod-shaped ε-Cu phase.
In this work, a new and effective treatment on bamboo fiber (BF) is presented, and its effect on the interfacial bonding properties of the BF/resin matrix was studied. The interfacial functionary ...mechanism of rare earth solution (RES) modification to improve the interfacial bonding properties between BF and the resin matrix was analyzed. The hardness and elastic modulus of the interfacial zone between BF and the resin matrix were measured using nanoindentation. Fourier-transform infrared spectroscopy (FT-IR) was used to analyze the change in the surface functional group of BF in the modification process. The surface chemical composition of BF before and after the modification was characterized by X-ray photoelectron spectroscopy (XPS). The results show that the RES modification significantly increases the hardness and elastic modulus of BF and its interfacial zone with the resin matrix. The hydroxyl concentration on the surface of RES-treated BF decreases, which reduces the hydrophilicity of BF. Rare earth ions react with oxygen in the hydroxyl group at the C2 position in the glucosylic ring of cellulose. The RES-modified BF bonds with the resin matrix to form a rare earth complex, which significantly enhances the interfacial adhesion between BF and the resin matrix.
Wire feeding speeds of 3.5, 4.5, and 5.5 m/min are operated to arc-braze TC4 titanium alloy to 304 L stainless steel with the cold metal transfer method and CuNi filler wire. The microstructure and ...fracture behavior of TC4−304Ldissimilar joints were characterized by transition electron microscopy (TEM), selected area electron diffraction (SAED) patterns and X-ray microscope (XRM). The results show that the TC4/seam transition zone consists of an inner Ti-rich layer and an outer Ti-poor layer based on the line scanning result, which contains complex eutectic microstructures such as (Cu, Ni)Ti3, CuNiTi2, CuNiTi, (CuxNi1-x)Ti, and (Cu) solid solutions. The microstructure of the 304 L/seam interface consists of CuNi2Ti, (Cu, Ni) and (Fe, Ni) solid solutions. With increasing heat input, the thickness of the TC4/seam transition zone and the size of (Fe, Ni) dendrite grains increase, the ultimate tensile strength decreases from 350.8 to 230.5 MPa, and all samples fracture near TC4 side based on tensile samples and XRM results. The crack propagation is due to both the thickness of TC4/seam transition zone and a large amount of brittle CuNiTi equiaxial dendrite grains with a high hardness of 10.4 GPa.
The surface of TC11 titanium alloy was polished and strengthened using ultrasonic rolling process (USRP) technology. The effects of USRP on the surface quality, friction and wear properties, ...corrosion resistance, and wear mechanisms of TC11 titanium alloy at room temperature, low temperature (−60 °C), high temperature (400 °C), and in corrosive environments were investigated by using optical microscope, microhardness tester, electrochemical workstation, multifunctional friction and wear tester, SEM, EDS, XRD, and XPS. The results indicate that USRP can effectively refine the surface grains of titanium alloy, reducing its surface roughness parameter by 80.4 % and increasing surface hardness and residual compressive stress by 21.7 % and 97.1 %, respectively. USRP is advantageous for producing a layer of TiO2 on the surface of titanium alloys, effectively enhancing the corrosion resistance of titanium alloy surfaces. USRP technology can improve the stability of surface hardness values of titanium alloys in harsh environments. The results of dry friction and wear tests using GCr15 steel balls as the counter material show that the USRP technology can effectively reduce the friction coefficient and wear loss at room, high and low temperatures. The results of corrosion and wear tests using Si3N4 as the counter material indicate that the USRP technology can effectively reduce the friction coefficient and wear volume in seawater corrosion environments. The USRP technology is most effective in reducing the high-temperature friction coefficient of titanium alloys and improving their wear resistance in low-temperature and corrosive environments. The primary wear form of TC11 titanium alloy after USRP has shifted from adhesive wear to abrasive wear.
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•The surface of TC11 was polished and strengthened using USRP technology.•The friction-wear and corrosion-wear behaviors of TC11 under extreme conditions were investigated.•USRP can effectively reduce the friction coefficient and wear under extreme conditions.•The corrosion and wear mechanisms of surface strengthened TC11 were revealed.
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