Wuzhou University

Wu H., Zhang S., Wang Z.Y., Zhang C.H., Chen H.T., Chen J.

In this paper, the wear and corrosion resistance of FeNiCoCrMo x (x: atomic ratio, x = 0, 0.15, 0.20, 0.25) high entropy alloy coatings (HEACs) which prepared by laser cladding (LC) technology on 316 stainless steel (SS) was investigated. According to XRD, SEM, MicroXAM-3D, microhardness tester and electrochemical workstation tests results, the HEACs presented typical DR-ID structure with single FCC solid solution phase. The average microhardness of Mo0, Mo0.15, Mo0.20 and Mo0.25 HEACs increased by 70.1%, 77.0%, 84.9% and 90.5% relative to the substrate. Dry sliding friction and wear tests results showed that the average friction coefficient of the HEACs were significantly lower than that of 316 SS substrate. Meanwhile, it can be found that Mo0.25 HEACs had the lowest average friction coefficient which displayed the best wear resistance. Compared with Mo0 HEAC, the specific wear rates of Mo0.15, Mo0.20 and Mo0.25 HEACs decreased by 11.1%, 27.8% and 38.9% respectively. The electrochemical tests results showed that the corrosion type of HEACs was intergranular corrosion and all HEACs had a higher corrosion resistance than that of 304 SS or 316 SS. Moreover, Mo0.20 HEACs showed the best corrosion resistance due to the enhancing effect of MoO 3 on Cr 2 O 3 passivation film. • The enhancement effect of Mo on wear resistance and corrosion resistance was explored. • The conclusions provide a reference for expanding the application range of 316stainless steel FeNiCoCrMo x HEACs.

Wu H., Xia Y., Zhang C., Xie S., Wu S., Cui H.

Deng X., Qin S., Huang J.

• A gradient hierarchical multicellular column evolved from the spatial folding is proposed. • Its specific energy absorption can increase by 27% to 98% compared with the square tube. • Novel columns with smaller height and larger wall thickness tend to form the compact mode with better performances. • Simplified super folding element theory can be used to predict its mean crush force with high accuracy. Based on the gradient hierarchical distribution of vascular bundles of bamboo, a gradient hierarchical multicellular column (GHMC) evolved from the spatial folding was proposed. Crashworthiness analysis of GHMC was carried via Abaqus/Explicit. Results show that the proposed GHMC has better energy absorption ability compared with the square tube under the same thickness or the same mass. The folding wavelength of GHMC is significantly decreased and it can produce more number of folds compared with the square tube. Under the condition of the same mass, the peak crushing force of GHMC decreases meanwhile its energy absorption increase by 10.1% to 72.44% compared with the square tube. Effect of hierarchical level and cell wall thickness on the energy absorption and their deformation mode under different height-length ratio ( H / L ) and cell wall thickness have been analyzed. Simplified super folding element theory was used to predict the mean crush force of GHMC, and the results were in good agreement with the simulations.

Luo R., Sun S., Zhang X., Tang Z., Wang W.

As surface electromyogram (sEMG) signals have the ability to detect human movement intention, they are commonly used to be control inputs. However, gait sub-phase classification typically requires monotonous manual labeling process, and commercial sEMG acquisition devices are quite bulky and expensive, thus current sEMG-based gait sub-phase recognition systems are complex and have poor portability. This study presents a low-cost but effective end-to-end sEMG-based gait sub-phase recognition system, which contains a wireless multi-channel signal acquisition device simultaneously collecting sEMG of thigh muscles and plantar pressure signals, and a novel neural network-based sEMG signal classifier combining long-short term memory (LSTM) with multilayer perceptron (MLP). We evaluated the system with subjects walking under five conditions: flat terrain at 5 km/h, flat terrain at 3 km/h, 20 kg backpack at 5 km/h, 20 kg shoulder bag at 5 km/h and 15° slope at 5 km/h. Experimental results show that the proposed method achieved average classification accuracies of 94.10%, 87.25%, 90.71%, 94.02%, and 87.87%, respectively, which were significantly higher than existing recognition methods. Additionally, the proposed system had a good real-time performance with low average inference time in the range of 3.25 ~ 3.31 ms.

Deng X., Qin S.

This paper proposes novel re-entrant honeycombs (NREH), which are designed as the support ribs of the re-entrant honeycomb subunit in an asymmetrical form to further improve its mechanical properties. First, three types of NREH composed of asymmetric subunits are compared. The σm and specific energy absorption (SEA) of the three NREHs are not much different during in-plane impact, while the Poisson's ratio of NREH-3 is smaller than that of the other NREHs. Analyze the performance of NREH-3 by analyzing the change of angle θ. It was found that in the y-direction, the SEA of NREH-3-80 is 41.46% higher than that of NREH-3-60, and the Poisson's ratio is almost unchanged. On x-direction, the energy absorption performance is not significantly improved. Analysis of NREH-3′s sensitivity to impact velocity revealed that NREH-3-60, NREH-3-70, and NREH-3-80 are greatly affected by impact velocity. As the velocity increases, their deformation models significantly change, while other structures remain constant. An analysis of the influence of NREH-3 on wall thickness showed that the SEA of NREH-3 is significantly improved with increasing wall thickness and that Poisson's ratio did not significantly change, indicating that appropriately increasing the wall thickness effectively improves the impact resistance of the honeycomb structure.

Wu C.L., Xu T.Z., Wang Z.Y., Zhang C.H., Zhang S., Ni C.L., Zhang D.X.

FeCoCrAlNiTi + x %TiC ( x = 10 and 30) high entropy alloy (HEA) composite coatings were deposited by laser surface alloying (LSA), aiming at studying the influence of TiC addition on wear resistance. The formed phases, microstructural evolution, hardness and wear behavior of the HEA composite coatings before and after 10-h anneal at 700 °C were clarified in detail by using XRD, SEM, EDS, Vickers hardness measurement and linearly reciprocating friction-wear measurement. The results displayed that three-phase FCC + BCC + TiC was appeared for HEA composite coatings with x = 10 and 30. The formed phases for the HEA coatings with x = 10 and 30 remained unchanged after 10-h annealing at 700 °C. The coatings exhibited dense microstructures, in addition to a good metallurgical bonding to the substrate. TiC particles displayed relatively homogeneous distribution in the matrix for HEA composite coatings with x = 10 and 30. The grains of the HEA matrix were obviously refined due to the TiC particles addition. The nano-hardness ( H ), nano-hardness/elastic modulus ( H / E ) and ( H 3 / E 2 ) of HEA composite coatings was obviously increased with the addition of TiC and the HEA composite coatings with x = 30 showed the highest nano-hardness, the ratio of H / E and H 3 / E 2 , possessing high resistance to plastic deformation. With the increase in nano-hardness, the specific wear rate of the HEA composite coatings with x = 30 was the lowest with the value of 2.636 × 10 −5 mm 3 /N m, indicating that it possessed the highest wear resistance. In addition, the HEA composite coatings in the current study also displayed an enhanced wear performance compared to the monotonous FeCoCrAlNiTi HEA coating reported in previous work.

Nie M.H., Zhang S., Wang Z.Y., Zhang C.H., Chen H.T., Chen J.

17-4PH stainless steel coatings is widely used in the field of laser repair due to its excellent performance. In the service process, the coatings not only have excellent mechanical properties but also ensure the formation of an excellent metallurgical bond between the coatings and the substrate. In this paper, the formability, microstructure evolution, texture characterization, microhardness and interface bonding strength of laser cladding 17-4PH stainless steel coatings under different laser powers are studied. A novel test method and related fixture are designed to analyze the interface fracture behavior of T-shaped specimens and evaluate the bonding strength. The relationship between microstructure and interfacial bonding strength of T-shaped specimens is investigated by electron backscattering diffraction (EBSD) and a universal testing machine. The higher stress concentration at the interface and heat-affected zone has been found by comparing the coatings. When the laser power is 2200 W, the microhardness and interfacial bonding strength are higher than other specimens, which are 450 HV and 908 MPa, respectively. This phenomenon is due to the appropriate laser power refines grains and reduces micro defects at the interface, which all contribute to improving the interfacial bonding strength. Fracture analysis shows that the combination of microvoids and unmelted powder contributed to accelerating the propagation of cracks. • A novel test method for measuring the normal bonding strength of the interface. • Specially T-shaped specimen and corresponding fixture were designed. • The interfacial strength was tested using a quasi-static tension method. • The effect of laser power on the formability and interfacial bonding strength of the specimens was studied.

Chen Q., Song Y., Zhao J.

Due to the characteristics of time-varying traffic and nonlinearity, the short-term traffic flow data are difficult to predict accurately. The purpose of this paper is to improve the short-term traffic flow prediction accuracy through the proposed improved wavelet neural network prediction model and provide basic data and decision support for the intelligent traffic management system. In view of the extremely strong nonlinear processing power, self-organization, self-adaptation and learning ability of wavelet neural network (WNN), this paper uses it as the basic prediction model and uses the particle swarm optimization algorithm for the slow convergence rate and local optimal problem of WNN prediction algorithm. With the advantages of fast convergence, high robustness and strong global search ability, an improved particle swarm optimization algorithm is proposed to optimize the wavelet neural network prediction model. The improved wavelet neural network is used to predict short-term traffic flow. The experimental results show that the proposed algorithm is more efficient than the WNN and PSO–WNN algorithms alone. The prediction results are more stable and more accurate. Compared with the traditional wavelet neural network, the error is reduced by 14.994%.

Qin S., Deng X., Liu X.

Hierarchical structures and gradient structures have become research hotspots due to their excellent crashworthiness. However, hierarchical gradient structures that combine hierarchical structures and gradient structures are rarely reported. Inspired by the gradient distribution of biological structure vascular bundles and the excellent energy absorption capacity of hierarchical structures, this paper innovatively combines hierarchical structures and gradient structures to propose a new type of bioinspired hierarchical gradient multicell tube (BHGMT). Crashworthiness studies have shown that the high-order BHGMT has a much better crashworthiness than the low-order BHGMT. The specific energy absorption of the 4th order BHGMT under the same mass is 216.26% that of the 0th order BHGMT. A comparison with other existing hierarchical structures under the same mass conditions shows that the proposed hierarchical gradient structure also has better crashworthiness. Subsequently, the systematic development of the influence of structural parameters such as hierarchy, section thickness, and crisscross rib thickness on the parameterization of BHGMT was carried out. Finally, theoretical research on the mean crushing force of the 3rd order BHGMT was carried out, and the theoretical solution was shown to be in agreement with the numerical simulation results. • Bioinspired hierarchical gradient multicell tubes are proposed to enhance crashworthiness. • Introduction of hierarchical gradients can effectively improve various crashworthiness indicators. • The influence of different crisscross ribs thickness on crashworthiness is studied. • A theoretical model is proposed to predict the mean crushing force of bioinspired hierarchical gradient multicell tubes.

Deng X., Qin S., Huang J.

A new type of axially varying thickness lateral corrugated tube (AVTLCT) is proposed. The crashworthiness of the AVTLCT under axial impact has been systematically studied. The studies show that the initial peak crushing force ( PCF ) increases as the amplitude increases and axial variation coefficient ( k ) decreases. The starting positions of all folds of the AVTLCT with axial variation coefficient k >0 are near the impact end. As the number of corrugations increases, the number of folds decreases and the fluctuation of the AVTLCT increases during the impact. Compared with the AVTLCT with k = 0 , the AVTLCT with k >0 has absolute advantages in the two key crashworthiness indicators, PCF and crush force efficiency ( CFE ). PCF is reduced by up to 44.53%, and CFE is increased by up to 81.72%. Finally, a surrogate model of the AVTLCT is constructed using the radial basis function approximation, and the interactive effects of structural parameters on crashworthiness indicators are analyzed. The nondominated sorting genetic algorithm II is used to perform multiobjective optimization under unconstrained and constrained conditions. • A new type of axially varying thickness lateral corrugated tube (AVTLCT) is proposed. • The crashworthiness of AVTLCT under axial impact is systematically studied. • Multi-objective optimizations of AVTLCT under different constrained conditions are performed.