Search

International audience; A simplified 3D FE model based on McCormick's model is developed to numerically predict the spatiotemporal behaviors of the PLC effect in Ti-12Mo alloy tensile tests at 350 degrees C with strain rates from the order of 10(-4) s(-1) to 10(-2) s(-1). The material parameter identification procedure is firstly presented in details, and the simulated results are highly consistent with experimental ones, especially in terms of stress drop magnitudes and PLC band widths. The distribution of simulated stress drop magnitudes at a constant tensile velocity (0.01 mm/s) follows a normal distribution and its peak value is in the range of 26-28 MPa. Furthermore, the simulated band width slightly fluctuates with the increase of true strain and its average value is about 1.5 mm. Besides, the staircase behavior of strain-time curves and the hopping propagation of the PLC band are observed in Ti-12Mo alloy tensile process, which are related to the strain localization and stress drop magnitudes.

A terahertz thermally tuned window based on the combination of metamaterial with the phase change material VO2 is proposed. It can be used as a smart window, regulating absorption and transmission of external terahertz waves in response to temperature.

Texture and coating technology can significantly improve the tribological properties of mechanical components. In this study, the lubricating and wear properties of the reticular surface texture under the action of TiN were studied. Lubrication and wear experiments at different speeds were conducted using a UMT-3 wear and friction testing machine. Using Fluent fluid simulation, the bearing capacity of the oil film was obtained, and the lubrication performance of the texture was verified. The results showed that the simulation experiment and the lubrication experiment were consistent to a certain extent. For the groove width and angle parameters studied in this paper, optimal parameters existed to achieve the maximum bearing capacity, 1.27 N. Due to the high hardness and low elastic modulus of the TiN coating, the coated reticular texture was more wear-resistant, and it achieved the minimum wear volume 1.148 × 10−6 mm3 from the grinding stainless-steel matrix. The effect of the fluid dynamic pressure, wear debris collection, and lubricating oil storage were the main reasons for the increase in load-carrying capacity and the decrease in wear with the coated reticular texture.

In this paper, a numerical model of elastohydrodynamic lubrication (EHL) in the line contact which happens on the surface of particle-reinforced composites is given. The influence of the particle size and burial depth on the EHL is studied. According to the influence of the structural parameters on the friction coefficient of the EHL contact, the structural parameters of the particles in the composites are optimized and the proper region of the parameters is obtained. The displacement and stress in elastic field caused by the uniform eigenstrains in the particles are described in terms of Galerkin vectors with the interactions between the particles are ignored. A coupling method of particle reinforced composites problem and EHL problem is presented, a new film thickness function is given considered the uneven elastic deformation caused by the presence of the particles. Finally, the presentation of film thickness and fluid pressure of the EHL explains that appropriate particle size, particle burial depth and particle distance can effectively reduce the friction coefficient. The lubrication behavior between the contacted surfaces can be improved under the heavy load.

Research to achieve a reasonable distribution of the slip zone of the sliding pair for better improvement of the hydrodynamic pressure of the liquid film is an intractable topic. To solve this issue, this paper takes the thrust bearing as the research object, and proposes to use the position number of the grid nodes at the boundary line between the slip and no-slip zone in each radial zone of the inclined pad to be variables. The variables are then defined as chromosomes in an adaptive genetic algorithm (AGA) and used to optimize the bearing capacity of the tilting pad. The results show that the optimal method of the AGA, which has good stability and repeatability, remarkably improves the distribution of the slip zone on the surface of the inclined pad. Therefore, the bearing capacity of the liquid film is significantly improved. Particularly, by using the optimization, the boundary line between the slip/no-slip zone is a composite form of a part of an arc and a part of the whisker. When the liquid flow through the heterogeneous slip/on-slip surfaces is used by this composite splicing method, the liquid pressure is upgraded in two steps. This is more conducive to increasing the pressure on multiple areas on the surface of the tilting pad, thereby achieving higher bearing capacity.

The microstructure and room-temperature tensile deformation behavior of the cast CrFeCoNiAl0.7 high-entropy alloy (HEA) were studied in details. The cast HEA consisted of a dual-phase structure of 77. 3 vol. % face-centered-cubic (FCC) phase plus 22.7 vol.% B2 phase, and exhibited excellent room-temperature tensile properties with a high yield strength of 876 MPa, ultimate tensile strength of 1198 MPa and a relatively large elongation to fracture of ∼9 %. Dislocations gliding in the FCC phase governed the plastic deformation at the early stage of room-temperature tensile, and disordered dislocations were to form dislocation walls as the deformation proceeded. With further increase in strain to a high level, the stacking faults were generated through the dissociation of the geometrically necessary dislocations, serving as the potential heterogeneous nucleation sites for the deformation twins.

N-ary gray-level (nGL) coding strategy is an effective method for absolute phase retrieval in the fringe projection technique. However, the conventional nGL method contains many unwrapping errors at the boundaries of codewords. In addition, the number of codewords is limited in only one pattern. Consequently, this paper proposes a new gray-level coding method based on half-period coding, which can improve both these two deficiencies. Specifically, we embed every period with a 2-bit codeword, instead of a 1-bit codeword. Then, special correction and decoding methods are proposed to correct the codewords and calculate the fringe orders, respectively. The proposed method can generate n2 codewords with n gray levels in one pattern. Moreover, this method is insensitive to moderate image blurring. Various experiments demonstrate the robustness and effectiveness of the proposed strategy.

In this paper, the interaction mechanism between the solid–liquid–gas interface phenomenon caused by nanostructure and surface wettability and boiling heat transfer is described, and the heat transfer theory of single wettable nanostructure surface and mixed wettable nanostructure surface is proposed. Through molecular dynamics simulation, the thermodynamic model of the wettable surface of nanostructures is established. The nanostructures are set as four rectangular lattice structures with a height of 18 Å. The solid atoms are platinum atoms, and the liquid atoms are argon atoms. The simulation results show that with the increase of surface hydrophilicity of nanostructures, the fluid temperature increases significantly, and the heat transfer at the interface is enhanced. With the increase in surface hydrophobicity of nanostructures, the atoms staying on the surface of nanostructures are affected by the hydrophobicity, showing a phenomenon of exclusion, and the evaporation rate in the evaporation area of nanostructures is significantly increased. In addition, the mixed wettable surface is influenced by the atomic potential energy and kinetic energy of the solid surface, and when compared with the pure wettable surface under the nanostructure, it changes the diffusion behavior of argon atoms on the nanostructure surface, enhances the heat transfer phenomenon compared with the pure hydrophobic surface, and enhances the evaporation phenomenon compared with the pure hydrophilic surface. This study provides insights into the relationship between the vapor film and the heating surface with mixed wettability and nanostructures.

In the present study, we selected solutes to be added to the CrCoNi medium-entropy alloy (MEA) based on the mismatch of self-diffusion activation energy (SDQ) between the alloying elements and constituent elements of the matrix, and then investigated their grain growth behavior and mechanical properties. Mo and Al were selected as the solutes for investigation primarily because they have higher and lower SDQ, respectively, than those of the matrix elements; a secondary factor was their higher and lower shear modulus. Their concentrations were fixed at 3 at.% each because previous work had shown these compositions to be single-phase solid solutions with the face-centered cubic structure. Three alloys were produced by arc melting, casting, homogenizing, cold rolling and annealing at various temperatures and times to produce samples with different grain sizes. They were (a) the base alloy CrCoNi, (b) the base alloy plus 3 at.% Mo, and (c) the base alloy plus 3 at.% Al. The activation energies for grain growth of the CrCoNi, CrCoNi-3Mo and CrCoNi-3Al MEAs were found to be ∼251, ∼368 and ∼219 kJ/mol, respectively, consistent with the notion that elements with higher SDQ (in this study Mo) retard grain growth (likely by a solute-drag effect), whereas those with lower values (Al) accelerate grain growth. The room-temperature tensile properties show that Mo increases the yield strength by ∼40 % but Al addition has a smaller strengthening effect consistent with their relative shear moduli. The yield strength as a function of grain size for the three single-phase MEAs follows the classical Hall-Petch relationship with much higher slopes (＞600 MPa μm−0.5) than traditional solid solutions. This work shows that the grain growth kinetics and solid solution strengthening of the CrCoNi MEA can be tuned by selecting solute elements that have appropriate diffusion and physical properties.

A numerical solution for line contact elastohydrodynamic lubrication (EHL) occurring on the rough surface of heterogeneous materials with a group of particles is presented in this study. The film thickness disturbance caused by particles and roughness is considered into the solution system, and the film pressure between the contact gap generated by the particles and the surface roughness is obtained through a unified Reynold equation system. The inclusions buried in the matrix are made equivalent to areas with the same material as that of the matrix through Eshelby’s equivalent inclusion method and the roughness is characterized by related functions. The results present the effects of different rough topographies combined with the related parameters of the particles on the EHL performance, and the minimum film thickness distribution under different loads, running speeds, and initial viscosities are also investigated. The results show that the roughness morphology and the particles can affect the behavior of the EHL, the traction force on a square rough surface is smaller, and the soft particles have more advantages for improving the EHL performance.

In this research, a novel vortex generator (VG) is presented. The experimental and numerical investigations were carried out to study the micro thermal-hydraulic performance in a heated tube. The numerical results showed that the fluid in the core flow region and the near-wall region was fully mixed because of the longitudinal vortices created by the vortex generators. In addition, the experimental results showed that the heat transfer coefficient (h) decreased with the increasing pitch ratio (PR) value, while the friction coefficient exhibited the opposite trend. With the increasing ration angle (RA) numbers, the h values decreased while the f numbers increased. In addition, the maximum and minimum values of the fraction ratio were 1.66 and 4.27, while these values of the Nusselt number ratio were 1.24 and 1.83. The maximum thermal enhancement factor (TEF) was 1.21 when PR = 0.5, RA = 0° and Re = 9090. The heat transfer enhancement mechanism of the vortex generator is explained from the microscopic point of view.

Purpose The stepped topography of the friction pairs mainly causes the fluid film thickness to change in the direction of motion. In this region, there have very few topographical design methods for continuous or non-linear distribution of the fluid film. The purpose of this study is to analyze the effect of the curved surface on the performance of the liquid film. Design/methodology/approach First, a numerical simulation is used to solve the optimal bearing capacity and friction coefficient of the liquid film under the condition of the minimum film thickness. Then, the curved surface described by the sinusoidal curve equation is applied in the transitional region of maximum and minimum film thickness. The bearing capacity and the friction coefficient of the liquid film are respectively simulated and compared in the same condition of the minimum film thickness. Findings The research results show that the liquid film using the curved surface transition model, the optimal bearing capacity is significantly increased by 32 per cent while the optimal friction coefficient is clearly reduced by 38 per cent in comparison with using stepped surface model. Originality/value The friction pair with curved transition enables better lubrication performance of the liquid film and better adaptability under unstable conditions.

Purpose This paper aims to use the method of curve splicing to combine the slip zone and the no-slip zone to further improve the lubrication performance of the liquid film. The combination of the slip zone and the no-slip zone of an existing heterogeneous surface is still a single line stitching method so that a very large residual space at the surface of the friction pairs remains present, necessitating further improvement of the joining scheme between the slip zone and the no-slip zone in heterogeneous surfaces. Design/methodology/approach A set of discrete sinusoids is used as the splicing track for both the slip zone and the no-slip zone, the starting point and amplitude of the curve are introduced as the simulation variables and the effects of these variables on the bearing capacity and friction coefficient of the liquid film are comprehensively analyzed. Findings The results show that the method of selecting the sinusoidal curve as the slip zone and the no-slip zone trajectory, which is based on the existing method of linear stitching, can further enhance the bearing capacity and reduce the friction coefficient of the liquid film. Originality/value This method can further enhance the bearing capacity and reduce the friction coefficient of the liquid film.

The theory of improving the bearing capacity of fluid lubrication with a heterogeneous slip/no-slip surface has been proposed in recent years, and the extended Reynolds equation is the main...

The traditional calibration paradigms fail to give reliable and accurate results in case of low-quality 2D planar calibration plates. In this paper, an active method is proposed by employing an LCD panel for camera calibration. This method automatically generates a sequence of virtual patterns in different views by pre-defined transforms without manually manipulation or other equipment’s help to move the patterns. Then, the projections of virtual patterns are captured by a camera. The homography between projective patterns in virtual world coordinate and their images is calculated directly to obtain the camera parameters. Experimental results show that the calibration error is 0.018 pixel in terms of mean re-projection error by using 18 virtual patterns, which is significantly less than the state-of-the-art methods. The proposed scheme makes camera calibration flexible and easy to use.

This paper explores the synergy mechanisms that are associated with the coexistence of multiple textures, to improve the precision control of a hydraulic servo cylinder. Based on the classical Reynolds equation, it establishes a single-texture and a nine-texture model to compare and study the synergy of surface textures. The film thickness is obtained under different working conditions for 1 N. Based on this parameter, it compares the simulation results from the two models with the experimental results to determine if the friction coefficient is reduced when multiple textures exist. When multiple textures exist, the inlet pressures of the central texture increase, but the peak pressure and cavitation pressure decrease. The synergy of the textures acts as an ‘average pressure’ and causes the pressure to decrease, which directly decreases the shear force. As the area ratio of the texture increases, the beneficial effect from the synergy gradually increases and then decreases, which implies that there is an optimum area ratio. The depth of the texture was 10 μm and the optimum depth-to-diameter ratio was 0.009. When the speed increases for a light load, the oil film thickness increases. However, this phenomenon does not substantially change the synergistic effect.

The eccentricity of the piston in the continuous casting machine cannot be ignored, which not only increases the internal leakage of the hydraulic cylinder, but also increases the friction on the surface of the friction pair, and even has serious consequences such as deformation failure. In this work, the biomimetic micro-texture technology is used to construct the microtextures on the surface of the cylinder so that it produces a continuous centring force during operation, and the problem of piston eccentricity is corrected. Moreover, the influence of hydraulic cylinder operating parameters and biomimetic microtexture parameters on the dynamic pressure support force is also analysed. This has a very positive effect on improving the response frequency of the hydraulic cylinder and the working efficiency of the hydraulic system.

Objectives: The aim of the present work was to comparatively investigate the generation and characteristics of fretting and sliding wear debris produced by CuNiAl against 42CrMo4. Methods: Tribological tests were conducted employing a self-developed tribometer. Most experimental conditions were set the same except for the amplitudes and number of cycles. Morphological, chemical, microstructural and dimensional features of the worn area and debris were investigated using optical microscope (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) and a laser particle sizer. Outcomes: Not only wear scar profiles but also the wear debris color, distribution and generated amount under fretting and sliding wear modes were quite different, which can be attributed to the significant difference in wear mechanisms. Particle size analysis indicates that the fretting debris has a smaller size distribution range; the biggest detected fretting and sliding wear debris sizes were 141 μm and 355 μm, respectively. Both fretting and sliding debris are mainly composed of copper and its oxides, but the former shows a higher oxidation degree.

The internal leakage of a hydraulic cylinder is an inevitable hydraulic system failure that seriously affects the working efficiency of the hydraulic system. Therefore, it is very important to accurately identify and predict leakage data in the hydraulic cylinder. In this paper, a model is proposed to simulate a small internal leakage of hydraulic cylinders, to convert the amount of leakage of hydraulic oil into strain signals through high-precision strain gauges and to train the collected strain signals using various neural networks to form a computational model and obtain prediction results from the model. The neural networks applied in this paper are convolutional neural networks, BP neural networks, T-S neural networks and Elman neural networks. The predicted results of the neural network are compared with the actual leakage amount. The results show that the prediction accuracy of the above four kinds of neural networks are all above 90%, of which the convolutional neural network is the most accurate. This research provides scientific and technical support for measuring and predicting small leaks.

All-inorganic lead halide perovskite quantum dots (IPQDs) display some intriguing magnetic, electronic, and optical properties by introducing a transition metal Mn element. In this Letter, Mn-doped CsPb(BrCl)3 IPQDs with a cubic structure have been synthesized by the hot injection method. What make us excited is that the photoluminescence properties of a fixed ensemble of Mn-doped CsPb(BrCl)3 IPQDs systematically depend on the varying concentration. This experimental phenomenon can be well explained by the quantitative model based on photon reabsorption. The results combining experiments with theoretical models indicate that the photon reabsorption is of paramount importance in the analysis of the luminescence properties of colloidal quantum dots especially at high concentrations. Further analysis based on time-resolved fluorescence and transient absorption spectroscopy reveals the effect of the solution concentration on the Mn-doped CsPb(BrCl)3 IPQD exciton dynamics. The results suggest that exciton energy transfer can take place both inside and between IPQDs and also can be enhanced by increasing the concentration of a Mn-doped CsPb(BrCl)3 IPQD solution. These results are of great significance to accurately interpret and control the luminescence properties of IPQDs.

It is challenging to align multi-exposed images due to large illumination variations, especially in presence of saturated regions. In this paper, a novel image alignment algorithm is proposed to cope with the multi-exposed images with saturated regions. Specifically, the multi-exposed images are first normalized by using intensity mapping functions (IMFs) in consideration of saturated pixels. Then, the normalized images are coded by using the local binary pattern (LBP). Finally, the coded images are aligned by formulating an optimization problem by using a differentiable Hamming distance. Experimental results show that the proposed algorithm outperforms state-of-the-art alignment methods for multi-exposed images in terms of alignment accuracy and robustness to exposure values.

A punched delta winglet (PDW) was proposed and investigated numerically and experimentally in a turbulent flow. The effect of delta winglets with different punching holes on heat transfer performance was studied. The experimental results showed that the fluid in the core flow region and the near-wall region was fully mixed due to the blocking effect of the delta winglets on the fluid. Due to the guidance of the PDWs, the recirculation region in the near-wall region was diminished because of the impaction of the fluid from the core flow region, which enriched the local heat transfer rate in this area. However, the jet flow from the punched holes restrained the longitudinal vortices behind the vortex generators. As a result, the heat transfer coefficient was reduced slightly in this area and the pressure loss of the channel was decreased. Moreover, the heat transfer coefficient and friction factor were lower with the largest area of the hole. When the area of the punched holes was the same, the thermal enhanced factor (TEF) was the largest at the large width and low height of the hole. In addition, the heat transfer coefficient and friction factor increased with the decrease of pitch ratio ( PR ). The maximum TEF was 1.49 for PR = 1.0 , w = 6 m m , h = 2 m m at R e = 9090 , which provided a basis for practical application.

For the ring surface of a hydraulic cylinder, grid and striped textures have been demonstrated in many previous works to easily provide a conductive oil path, which increases the difficulty of generating converging wedges and are harmful to the formation of dynamic pressure lubrication, especially for full lubrication. Moreover, these studies used an orthogonal design method to study the hydrodynamic lubrication effect and friction performance of the surface without considering the comprehensive effect of multiple parameters with simultaneous changes, which may introduce errors into the simulation analysis. In this work, a diamond-like, non-conductive texture, which mimics shark skin, is developed and optimised to determine the optimal texture morphology while simultaneously considering the influence of multiple parameters, including the diamond angle, axial length ratio, and area occupancy, to optimise the surface of the friction pair. The results show that under the same working conditions, the lift of the diamond texture is nine times greater than that of the striped texture, while its friction coefficient is only one-quarter of that of the striped texture, which will greatly improve the friction and responsiveness of the hydraulic cylinder.

Purpose The purpose of this study is to establish a friction coefficient prediction model using texture parameters and then using the optimal texture parameters to obtain the minimum friction coefficient. Design/methodology/approach Based on texture technology and the cavitation phenomenon conditions, a test scheme based on two-factor and five-level texture parameters is designed using central composite design and then the response surface methodology and hybrid back-propagation genetic algorithm (BP-GA) models are used to establish a friction coefficient prediction model and optimize the friction coefficient. Findings The result indicates that the values predicted using two methodologies agree well with the experimental data, but the hybrid BP-GA model is superior to the response surface methodology model in both prediction and optimization. Originality/value Two methodologies are used to study the influence of the texture parameters on the friction coefficient under the cavitation condition. It is expected that the result can be used to obtain optimum texture parameters to reduce the friction coefficient.

The intelligent estimation of degradation state and the prediction of remaining useful life (RUL) are important for the maintenance of industrial equipment. In this study, the degradation process of equipment is modeled as an improved hidden semi-Markov model (HSMM), in which the dependence of durations of adjacent degradation states is described and modeled in the HSMM. To avoid underflow problem in computing the forward and backward variables, a modified forward–backward algorithm is proposed in the HSMM. Based on the improved algorithm, online estimation of degradation state and the distribution of RUL can be obtained. Case studies on tool wearing diagnosis and prognosis have verified the effectiveness of this model.

Core–shell Fe3O4@C magnetic nanoparticles which are of great interest for research have a widely applied prospect. However, people know little about the optical and magnetic properties of the small-size Fe3O4@C nanoparticles due to the difficulty of uniformly coating small size Fe3O4 nanoparticles. In this paper, the influence of carbon shell coating on the optical and magnetic properties of small size Fe3O4 nanoparticles was presented. Carbon coating can strengthen the absorption intensity in the UV–visible light region through the introduction of oxygen defects on the surface of the nanoparticles by nitric acid treatment. Fe3O4 and Fe3O4@C nanoparticles both display typical superparamagnetic behavior in the high-temperature regime and a blocked state at low temperature from hysteresis loop, zero-field cooled and field cooled curves. Carbon coating reduce the surface uniaxial anisotropy, thus the average blocking temperature decreases from 59 K of Fe3O4 nanoparticles to 50 K of Fe3O4@C nanoparticles.

Hot compression behaviors and microstructure evolutions of a cast dual-phase NiCoFeCrAl0.7 high-entropy alloy (HEA) consisting of 79.2 vol% face-centered-cubic (FCC) plus 20.8 vol% body-centered-cubic (BCC) phases were investigated under various parameters. Dynamic recrystallization (DRX) dominated the flow softening behavior, strongly depending on the hot compression parameters. The constitutive equation describing the correlations between the flow stress and hot compression parameters was constructed, and the activation energy of the dual-phase HEA was significantly improved up to approximately 379.81 kJ/mol. The curves of Xdrx (volume fraction of DRX grains) against the strain exhibits a “C” shape. Continuous dynamic recrystallization (CDRX) governed the flow softening, which was preferred in the FCC phase. With the proceeding of hot compression, the substructure within the deformed microstructure evolved in a sequence from the disordered dislocations, cellular structure, subgrain to DRX grains.

Investigations on the high-temperature tensile performances and deformation behaviors of the directionally solidified Ti–45Al–5Nb–2Mn alloy revealed that an increase in the tensile temperature resulted in the occurrence of brittle-ductile transition (BDT) and the BDT temperature was beyond 1173 K. The mixed mode of inter- and trans-lamellar fracture governed the brittle fracture, and except for dimples, there were split lamellae on the ductile fracture surface. The main cracks propagated along a tortuous path and multiple secondary cracks were formed adjacent to the main cracks. The dislocation mechanism controlled the high-temperature tensile deformation. The lamellar interface remained flat at 1073 K and 1173 K, but there was significant strain existing at the lamellar interface, which made the orientation relation of α2 lath and γ lath change to be ( 200 ) γ / / ( 01 1 ‾ 0 ) α 2 and [ 001 ] γ / / [ 0001 ] α 2 . At the tensile deformation of 1273 K, the lamellae coarsened irregularly by the phase degradation reaction of α2→γ and dynamic recrystallization.

Coarse grains are formed during thermomechanical processing for the widely studied NiCoCr medium-entropy alloy (MEA) due to the lack of effective approaches to restrain grain growth. Here, a novel integrated method combing solute drag and Zenner pinning effects are proposed. The 0.5 at.% C was added to precipitate carbides which generates pinning of the grain boundaries; while solute drag is implemented by 3 at.% addition of Mo with low self-diffusion coefficient. Results show that most of Mo is dissolved in the matrix and M23C6 carbides uniformly precipitated after aging. The combined method shows a significant effect on controlling grain growth and results in much finer equiaxed grains. A very high growth activation energy of 511 kJ / mol was obtained, double that of NiCoCr MEA (251 kJ / mol ). This work shows that the grain growth kinetics of the NiCoCr based MEA during traditional thermomechanical processing can be tuned by adjusting carbide precipitates and selecting appropriate solute elements.

In the present study, Ti-47Al-2Nb-2Cr-2Mn directionally solidified by electromagnetic cold crucible was mainly composed of alternatively arranged (α2 + γ) lamellae, and exhibited a room-temperature tensile ductility of 1.55%, and an ultimate strength of 587 MPa. At 800 °C ultimate strength remained high at 512 MPa, with 4.33% ductility. The crack propagated around B2 phase at room temperature, but cut though B2 phase at elevated temperature. Both dislocation slip and twinning governed the room-temperature plastic deformation, and the twin boundary acted as the obstacle to dislocation slip. The friction coefficient of the N-orientation (70°-90°) TiAl sample was the highest, followed by the I-orientation (35°-50°) and P-orientation (0°-15°) samples, while their wear rates presented an opposite trend. The P-orientation sample was more liable to form the tribo-oxide layer. Moreover, the local plastic deformation during dry sliding resulted in pile-ups along the edge of wear tracks.

The traditional estimation methods of space targets pose are based on artificial features to match the transformation relationship between the image and the object model. With the explosion of deep learning technology, the approach based on deep neural networks (DNN) has significantly improved the performance of pose estimation. However, the current methods still have problems such as complex calculation, low accuracy, and poor real-time performance. Therefore, a new pose estimation algorithm is proposed in this paper. Firstly, the mask image of the target is obtained by the instance segmentation algorithm, and its point cloud image is obtained based on a depth map combined with camera parameters. Finally, the correlation among points is established to realize the prediction of pose based on multi-modal feature fusion. Experimental results in the YCB-Video dataset show that the proposed algorithm can recognize complex images at a speed of about 24 images per second with an accuracy of more than 80%. In conclusion, the proposed algorithm can realize fast pose estimation for complex stacked objects and has strong stability for different objects.

Object detection and segmentation can improve the accuracy of image recognition, but traditional methods can only extract the shallow information of the target, so the performance of algorithms is subject to many limitations. With the development of neural network technology, semantic segmentation algorithms based on deep learning can obtain the category information of each pixel. However, the algorithm cannot effectively distinguish each object of the same category, so YOLOMask, an instance segmentation algorithm based on complementary fusion network, is proposed in this paper. Experimental results on public data sets COCO2017 show that the proposed fusion network can accurately obtain the category and location information of each instance and has good real-time performance.

A tunable terahertz (THz) narrowband absorber in view of bulk Dirac semimetal (BDS) is designed in this paper. The tunable terahertz absorber's basic unit comprises BDS, intermediate medium, and metal substrate. The BDS has good surface conductivity and the Fermi energy of that is flexible tunable, and the good surface conductivity might make controlled by Fermi energy. The absorption characteristics of the designed absorber are simulated by the finite integral time domain technique. The calculation results show that the designed absorber achieves ideal absorption in 139.97 μm, 163.52 μm, 247.76 μm bands, and the absorption rate is more than 0.96, which realizes ideal narrowband absorption and dynamic tuning. We find that the absorption peaks are flexible and adjustable by changing the Fermi energy of BDS, and the frequency adjustability of the absorber is analyzed. In addition, the effects of different structural parameters on the absorption efficiency and the absorption performance at different incident angles are studied. These results show that, compared with traditional metamaterials, Dirac semimetallic absorbing materials can tune the resonant frequency more effectively, even without reconstructing the structure, which has great application value in many fields, and provide a new reference for future research.

The plastic zones of crack tips play a significant role in the fracture behavior of material. This paper proposes a semi-analytic solution for the plastic zones and stress distribution of an infinite space with multiple cracks and inhomogeneous inclusions under remote stress. In this solution, cracks can be treated as a distribution of edge dislocations with unknown densities according to the distributed dislocation technique, while inhomogeneous inclusions can be modeled as homogeneous inclusions with initial eigenstrain plus the unknown equivalent eigenstrain by using the equivalent inclusion method. These unknowns can be obtained by using the conjugate gradient method. The plastic zones ahead of crack tips are one-dimensional slender strips, and their sizes can be determined by canceling the stress intensity factor (SIF) due to the closure stress and that due to the applied load based on the Dugdale model of small-scale yielding. It is found that the plastic zones of crack tips are significantly affected by Young’s modulus and the positions of inhomogeneous inclusions.

It is challenging to convert a hazy color image into a gray-scale image because the color contrast field of a hazy image is distorted. In this paper, a novel decolorization algorithm is proposed to transfer a hazy image into a distortion-recovered gray-scale image. To recover the color contrast field, the relationship between the restored color contrast and its distorted input is presented in CIELab color space. Based on this restoration, a nonlinear optimization problem is formulated to construct the resultant gray-scale image. A new differentiable approximation solution is introduced to solve this problem with an extension of the Huber loss function. Experimental results show that the proposed algorithm effectively preserves the global luminance consistency while represents the original color contrast in gray-scales, which is very close to the corresponding ground truth gray-scale one.

Droplet generation process can directly affect process regulation and output performance of electrohydrodynamic jet (E-jet) printing in fabricating micro-to-nano scale functional structures. This paper proposes a numerical simulation model for whole process of droplet generation of E-jet printing based on the Taylor-Melcher leaky-dielectric model. The whole process of droplet generation is successfully simulated in one whole cycle, including Taylor cone generation, jet onset, jet break, and jet retraction. The feasibility and accuracy of the numerical simulation model is validated by a 30G stainless nozzle with inner diameter ~160 &mu, m by E-jet printing experiments. Comparing numerical simulations and experimental results, period, velocity magnitude, four steps in an injection cycle, and shape of jet in each step are in good agreement. Further simulations are performed to reveal three design constraints against applied voltage, flow rate, and nozzle diameter, respectively. The established cone-jet numerical simulation model paves the way to investigate influences of process parameters and guide design of printheads for E-jet printing system with high performance in the future.