摘要：
Laser shock peening (LSP) was implemented to treat aircraft landing gear 50CrVA alloy to improve mechanical properties. The sensitivity investigations of time step and mesh size were used to benchmark the 3D finite element method (FEM) model. Based on the established FEM model, the dynamic propagation characteristics of the shock wave inside the sample were predicted. The influence of laser energy and spot diameter on the residual stress field was further investigated. The numerical results indicate that regulating two critical LSP parameters can effectively improve the compressive residual stress (CRS) of metals, and the spot diameter has a greater effect than the laser energy in improving the uniformity of the CRS distribution. After that, the influences of LSP on the CRS field, microstructure, and mechanical properties were experimentally studied. After LSP treatment, the surface CRS reached 494.8 +/- 31.8 MPa with an affected depth of about 400 mu m. The phase composition was not changed by LSP treatment, but it weakened texture strength and refines grains. Under the impact of grain refinement and CRS, the average surface microhardness of the 50CrVA alloy reached 355 HV, indicating an increase up to 5.3 %. The ultimate tensile strength and yield strength were increased by 11.3 % and 14.5 %, respectively, which were in contrast to the unchanged elongation. This work verifies the feasibility of mechanical properties enhancement of 50CrVA alloy by LSP.
关键词：
passion fruit epicarp;near-infrared spectroscopy;hardness;Grids-RF model;GA-SVR model
摘要：
The hardness of passion fruit is a critical feature to consider when determining maturity during post-harvest storage. The capacity of near-infrared diffuse reflectance spectroscopy (NIRS) for non-destructive detection of outer and inner hardness of passion fruit epicarp was investigated in this work. The passion fruits' spectra were obtained using a near-infrared spectrometer with a wavelength range of 10,000-4000 cm(-1). The hardness of passion fruit's outer epicarp (F1) and inner epicarp (F2) was then measured using a texture analyzer. Moving average (MA) and mean-centering (MC) techniques were used to preprocess the collected spectral data. Competitive adaptive reweighted sampling (CARS), successive projection algorithm (SPA), and uninformative variable elimination (UVE) were used to pick feature wavelengths. Grid-search-optimized random forest (Grids-RF) models and genetic-algorithm-optimized support vector regression (GA-SVR) models were created as part of the modeling process. After MC preprocessing and CARS selection, MC-CARS-Grids-RF model with 7 feature wavelengths had the greatest prediction ability for F1. The mean square error of prediction set (RMSE(P)) was 0.166 gN. Similarly, following MA preprocessing, the MA-Grids-RF model displayed the greatest predictive performance for F2, with an RMSE(P) of 0.101 gN. When compared to models produced using the original spectra, the R(2)(P) for models formed after preprocessing and wavelength selection improved. The findings showed that near-infrared spectroscopy may predict the hardness of passion fruit epicarp, which can be used to identify quality during post-harvest storage.
通讯机构：
[Man, JF ] H;Hunan First Normal Univ, Sch Intelligent Mfg, Changsha 410205, Hunan, Peoples R China.
摘要：
Based on the influence of a filamentous laser Gaussian heat source and its movement speed on Polymeric Methyl Methacrylate materials (PMMA sheets), the physical model of heat transfer of PMMA materials by CO2 continuous laser ablation was established. Numerical simulation research on heat transfer in CO2 continuous laser processing of PMMA sheets was carried out by applying the heat transfer model, and experiments on continuous laser processing of PMMA sheets were conducted on the basis of the numerical simulation results. Theoretical and experimental research indicated that under relevant conditions, when the laser power was 20 W, the maximum surface temperature of PMMA sheet was approximately 520 K, which was higher than the melting temperature of the PMMA material, achieving the transformation of the PMMA material from solid to liquid phase in the laser ablation area. When the laser power was 40 W, the CO2 continuous laser could vaporize the PMMA material, cracking the polymer structure of polymethyl methacrylate. When the laser power was 80 W, the maximum surface temperature of the PMMA sheet was approximately 1300 K, and the processing efficiency of CO2 continuous laser ablation of the PMMA material was the highest. The above research provided theoretical guidance and process optimization for the research of CO2 continuous laser ablation of PMMA sheets. The consistency between the experimental results and the numerical simulation results demonstrated the correctness and feasibility of the theoretical model, which has certain universality and reference value for the optimization research of laser processing non-metallic materials and polymer materials.
关键词：
Sb2S3;femtosecond laser direct writing;microstructure;spin coating;surface-enhanced Raman scattering
摘要：
The noble-metal-free surface-enhanced Raman scattering (SERS) substrates have gained significant attention due to their abundant sources, signal uniformity, biocompatibility, and chemical stability. However, the lack of controllable synthesis and fabrication methods for high-SERS-activity noble-metal-free substrates hinders their practical applications. In this study, we demonstrate the use of a femtosecond laser direct writing technique to precisely manipulate and modify microstructures, resulting in enhanced SERS signals from Sb(2)S(3) nonmetal-oxide semiconductor materials. Compared with unpatterned Sb(2)S(3) samples, the Sb(2)S(3) microstructures exhibited up to a 16-fold increase in Raman scattering intensity. Interestingly, our results indicate that the femtosecond laser can induce a transformation in the crystalline state of Sb(2)S(3) and significantly enhance the Raman spectrum signal within the Sb(2)S(3) microstructures. This enhancement is also highly dependent on the period and depth of the microstructures, possibly due to the cavity effects, resulting in a stronger local field enhancement.
关键词：
Passion fruit;Texture parameters;Correlation analysis;Pericarp change index
摘要：
This study aims to explore the changing trends in external characteristics of passion fruit pericarp and their application in predicting shelf-life, assessing storage quality, and advancing the field of non-destructive testing. Through storage experiments, the evolving patterns of passion fruit pericarp during storage and correlations among relevant physical parameters were analyzed. Three attribute parameters, namely minor-axis diameter, hardness, and mass, were extracted from the characteristic parameters of passion fruit, exhibiting the strongest interrelationships with storage time variable. The findings indicate a negative correlation between storage duration and minor-axis diameter of passion fruit, while no correlation was observed with major-axis diameter. The pericarp's contraction behavior is influenced by both thickness reduction and internal collapse. Moreover, a linear correlation existed between hardness of pericarp layers. The minor-axis diameter was positively correlated with puncture force at two peak positions (R = 0.87, P < 0.01; R = 0.95, P < 0.01). Simultaneously, minor-axis positively correlated with thickness and mass (R = 0.97, P < 0.01; R = 0.98, P < 0.01). To better quantify the degree of pericarp change, a passion fruit pericarp change index was proposed. Using the index as an independent variable and storage duration as the dependent variable, an equivalent fruit age prediction model was established. The results show a coefficient of determination (R-2) of 0.997 and a significance level of P < 0.05 between predicted and actual values. This research has the potential to provide a theoretical foundation and methodological framework for predicting passion fruit shelf-life in the context of food preservation and storage, and to offer practical support for real-world applications in the field.
关键词：
stability;polarization vortex;phase field simulations
摘要：
Mastering the variations in the stability of a polarization vortex is fundamental for the development of ferroelectric devices based on polarization vortex domain structures. Some phase field simulations were conducted on PbTiO3 nanofilms with an initial polarization vortex under uniaxial tension or compression to investigate the conditions of vortex instability and the effects of aspect ratio of nanofilms and temperature on them. The instability of a polarization vortex is strongly dependent on aspect ratio and temperature. The critical compressive stress increases with decreasing aspect ratio under the action of compressive stress. However, the critical tensile stress first decreases and then increases with decreasing aspect ratio, then continues to decrease. There are two inflection points in the curve. In addition, an elevated temperature makes both the critical tensile and compressive stresses decline, and will also cause the aspect ratio corresponding to the inflection point to decrease. These are very important for the design of promising nano-ferroelectric devices based on polarization vortices to improve their performance while maintaining storage density.
摘要：
Building heterojunctions is a promising strategy for the achievement of highly efficient photocatalysis. Herein, a novel SnIn4S8@ZnO Z-scheme heterostructure with a tight contact interface was successfully constructed using a convenient two-step hydrothermal approach. The phase composition, morphology, specific surface area, as well as photophysical characteristics of SnIn4S8@ZnO were investigated through a series of characterization methods, respectively. Methylene blue (MB) was chosen as the target contaminant for photocatalytic degradation. In addition, the degradation process was fitted with pseudo-first-order kinetics. The as-prepared SnIn4S8@ZnO heterojunctions displayed excellent photocatalytic activities toward MB degradation. The optimized sample (ZS800), in which the molar ratio of ZnO to SnIn4S8 was 800, displayed the highest photodegradation efficiency toward MB (91%) after 20 min. Furthermore, the apparent rate constant of MB photodegradation using ZS800 (0.121 min-1) was 2.2 times that using ZnO (0.054 min-1). The improvement in photocatalytic activity could be ascribed to the efficient spatial separation of photoinduced charge carriers through a Z-scheme heterojunction with an intimate contact interface. The results in this paper bring a novel insight into constructing excellent ZnO-based photocatalytic systems for wastewater purification.
作者：
Xu, T.;Mei, Q. S.;Liao, L. Y.;Ma, Y.;Chen, Z. H.;...
期刊：
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing,2023年874:145066 ISSN：0921-5093
通讯作者：
Mei, QS
作者机构：
[Mei, Q. S.; Liao, L. Y.; Xu, T.; Chen, Z. H.; Wang, Y. C.] Wuhan Univ, Sch Power & Mech Engn, Wuhan 430072, Peoples R China.;[Mei, Q. S.] Wuhan Univ, Minist Educ, Key Lab Hydraul Machinery Transients, Wuhan 430072, Peoples R China.;[Ma, Y.] Wuhan Univ, Core Facil Wuhan Univ, Wuhan 430072, Peoples R China.;[Li, J. Y.] Wuhan Polytech Univ, Sch Mech Engn, Wuhan 430023, Peoples R China.
通讯机构：
[Mei, QS ] W;Wuhan Univ, Sch Power & Mech Engn, Wuhan 430072, Peoples R China.;Wuhan Univ, Minist Educ, Key Lab Hydraul Machinery Transients, Wuhan 430072, Peoples R China.
关键词：
Al matrix composites;Mechanical properties;Strengthening behavior;Strain hardening
摘要：
Two types of Al matrix composites (AMCs) containing micro-sized B4C particles (m-B4C/Al) and nano-sized particles (n-B4C/Al) were prepared by hybrid accumulative roll-bonding. The influences of m-B4C and n-B4C particles on the microstructure and mechanical properties of the AMCs were investigated systematically. Microstructure observations showed that B4C particles were uniformly distributed in the matrix with well-bonded interfaces in both the two types of composites. The n-B4C/Al composites presented finer grain size compared to the m-B4C/Al, indicating that n-B4C particles are more effective in enhancing the grain refinement and suppressing the grain growth than m-B4C particles. While the n-B4C/Al composites exhibited higher microhardness and strength, the m-B4C/Al composites showed higher elongation. Moreover, the strain hardening rate of the n-B4C/Al composites was higher at the initial stage of plastic deformation, but lower than that of the m-B4C/Al composites at larger strain. Furthermore, nanoindentation tests showed an obvious increment of nanohardness with the increase of deformation in the m-B4C/Al composites. The different strengthening behaviors of m-B4C and n-B4C particles can be attributed to the particle-dislocation interactions at different stages of plastic deformation. This work demonstrated the significant differences between the deformation and strengthening behaviors of AMCs reinforced by micro- and nano-sized B4C particles, providing novel insights for the design of AMCs with high strength and toughness by taking advantages of the hybrid-sized reinforcement particles.
关键词：
Sc modification;DED;microstructure;mechanical property;heat-affected zone
摘要：
Aluminum alloy is an important material used in railway train structures. It is of great significance to repair aluminum alloy through directional energy deposition to reduce cost and improve the performance of the aluminum alloy. In this study, 7N01 aluminum alloy was repaired by means of laser-directed energy deposition (DED) with the powder of Sc-modified Al-Zn-Mg aluminum alloy as raw material. The microstructure and mechanical properties of the repaired specimens were studied through the metallographic microscope, scanning electron microscope, electron backscatter diffraction, universal tensile test, and Vickers hardness test in combination. The results show that the bonding interface of the repaired aluminum alloy is satisfactory, and the porosity is 2.8%. The grains in the repaired area are the columnar crystals growing vertically along the boundary of the melt pool with an obvious temperature gradient. Fine equiaxed crystals are distributed along the boundary of the melt pool, and Al-3(Sc,Zr) particles play a role in grain refinement. The average grain size of the fine grain area in the repair zone next to the fusion zone is 9.1 mu m, and the average grain size of the coarse grain area is 20 mu m. The average tensile strength in the area of repair approaches 349 MPa, which is 91% that of the base material, and the elongation rate is 10.9%, which is 53.2% that of the base material. The hardness ranges between 122 HV and 131 HV, which is comparable to the base material. However, there is a significant decrease in the tensile strength and hardness of the base material (heat-affected zone).
通讯机构：
[Pei, HC ] W;[Xing, L ] N;Wuhan Polytech Univ, Sch Mech Engn, Wuhan 430048, Peoples R China.;Northumbria Univ, Mech & Construct Engn, Newcastle Upon Tyne NE1 8ST, England.
关键词：
Air-cooled PEMFC stack;air supply mode;temperature distribution;multizone temperature measurement;blowing air supply mode;suction air supply mode
摘要：
Open-cathode air-cooled proton exchange membrane fuel cell stack relies on air fans both for fuel supply and stack cooling. Inappropriate stack thermal management and non-uniform temperature distribution can lead to compromised stack performance, reduced lifespan, and even thermal runaway. Thus, temperature distribution measurement, investigation and analysis are essential for air-cooled PEMFC's optimized operation and performance. This study uses a multi-zone temperature measurement approach to investigate the impact of air supply method, airflow, and output current on stack temperature distributions. The experimental results reveal that the highest stack temperature occurs at the cathode channel outlet, while the lowest temperature is near the hydrogen inlet. At a 75A load, the maximum temperature difference between the inlet and outlet is 17 degrees C. Increasing fan speed from 4500 to 8800 r/min reduces temperature non-uniformity in cell 10, the most uneven among the 19 cells, by 11.2%. Comparing blowing and suction air supply modes, blowing enhances stack output performance by 2.1%, with smaller temperature differences. Specifically, cell 10 experiences a 7.5 degrees C lower difference at 4500 r/min and a 3.6 degrees C lower difference at 8800 r/min airflow. Under blowing air supply, temperature non-uniformity decreases by 36.95% at 4500 r/min and 29.2% at 8800 r/min.
摘要：
As living standards rise, people have higher requirements for the quality of duck eggs. The quality of duck eggs is related to their origin. Thus, the origin traceability and identification of duck eggs are crucial for protecting the rights and interests of consumers and preserving food safety. As the world's largest producer and consumer of duck eggs, China's duck egg market suffers from a severe lack of duck egg traceability and rapid origin identification technology. As a result, a large number of duck eggs from other regions are sold as products from well-known brands, which seriously undermines the rights and interests of consumers and is not conducive to the sound development of the duck egg industry. To address the above issues, this study collected visible/near-infrared spectral data online from duck eggs of three distinct origins. To reduce noise in the spectral data, various pre-processing algorithms, including MSC, SNV, and SG, were employed to process the spectral data of duck eggs in the range of 400-1100 nm. Meanwhile, CARS and SPA were used to select feature variables that reflect the origin of duck eggs. Finally, classification models of duck egg origin were developed based on RF, SVM, and CNN, achieving the highest accuracy of 97.47%, 98.73%, and 100.00%, respectively. To promote the technology's implementation in the duck egg industry, an online sorting device was built for duck eggs, which mainly consists of a mechanical drive device, spectral software, and a control system. The online detection performance of the machine was validated using 90 duck eggs, and the final detection accuracy of the RF, SVM, and CNN models was 90%, 91.11%, and 94.44%, with a detection speed of 0.1 s, 0.3 s, and 0.5 s, respectively. These results indicate that visible/near-infrared spectroscopy can be exploited to realize rapid online detection of the origin of duck eggs, and the methodologies used in this study can be immediately implemented in production practice.
期刊：
Journal of Materials Engineering and Performance,2023年32(1):135-143 ISSN：1059-9495
通讯作者：
Jili Liu<&wdkj&>Junsheng Yang
作者机构：
[Li, Jiang; Liu, Jili; Li, Xide; Liu, Yuzuo; Zhu, Yan] Wuhan Univ Technol, Dept Mech & Engn Struct, Wuhan 430070, Peoples R China.;[Fan, Yiquan; Yang, Junsheng; Liu, Yuzuo] Wuhan Polytech Univ, Sch Mech Engn, Wuhan 430048, Peoples R China.;[Liu, Jili] Wuhan Univ Technol, Hubei Key Lab Theory & Applicat Adv Mat Mech, Wuhan 430070, Peoples R China.;[Liu, Bing] Wuhan Second Ship Design & Res Inst, Wuhan 430064, Peoples R China.
通讯机构：
[Jili Liu] D;[Junsheng Yang] S;Department of Mechanics and Engineering Structure, Wuhan University of Technology, Wuhan, China<&wdkj&>Hubei Key Laboratory of Theory and Application of Advanced Materials Mechanics, Wuhan University of Technology, Wuhan, China<&wdkj&>School of Mechanical Engineering, Wuhan Polytechnic University, Wuhan, China
摘要：
Hot isostatic pressing (HIP) has an important influence on the pore closure behavior and the microstructure evolution around pores in Ti6Al4V alloy castings. Therefore, experiments including the preparation of HIP samples and interrupted HIP experiments, and finite element numerical simulations were used to analyze the evolution of pore volume, distribution of stress and strain in Ti6Al4V alloy during HIP. After the mechanical closure of pores, molecular dynamics simulations were used to study the effect of temperatures and numbers of grains on the micropore closure. Finally, SEM/EBSD methods were applied to characterize the evolution of microstructure around the pore. The results show that creep is mainly contributed to the pore closure in the Ti6Al4V alloy during HIP, and the pore volume decreases by 96% after the step of raising temperature and pressure (first stage of HIP), the pore closure mainly occurs in the first stage of HIP. Grain boundary diffusion is the main mechanism for micropore closure. In addition, with the increase of HIP duration, the volume fraction of spheroidized a grains around pores is getting larger, the main mechanisms of spheroidization of a lamellae around the pore during HIP are continuous dynamic recrystallization and lamellae kinking. & COPY; 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
通讯机构：
[Li, B ] W;Wuhan Polytech Univ, Sch Mech Engn, Wuhan 430023, Peoples R China.
关键词：
ribbed laminated cylinder shell;micro-perforated shell;acoustic radiation;finite element analysis
摘要：
In response to the problem of vibration and noise reduction in equipment with cylindrical shell structures, this paper focuses on the micro-perforated laminated cylindrical shell structure and establishes its finite element model. Through comparative analysis with experimental results, the reliability of the finite element modeling method is verified. Based on this, the paper places particular emphasis on the vibration and acoustic radiation performance of the structure in the 1–1000 Hz frequency range under free conditions to understand the impact of different laminated shell structures, micro-perforation parameters (porosity, aperture), sound-absorbing foam materials, and placement methods. The results indicate that micro-perforated structures can efficiently reduce the structural radiated sound power level at specific frequencies, but the overall reduction in radiated sound power level is not significant. Various types of foam are effective in reducing the structural radiation acoustic power level, with polyurethane performing best among them. Changing the location of foam placement has a relatively insignificant impact on the structural radiation acoustic power level.
通讯机构：
[Yang, L ] W;Wuhan Polytech Univ, Coll Mech Engn, Wuhan 430048, Hubei, Peoples R China.
关键词：
Brown rice kernel;Bio-structure;Starch granules;Fracture mechanics
摘要：
The microscopic and macroscopic structure of brown rice kernel determines that it is a complex bio-material. Therefore, revealing kernel structural characteristics and fracture mechanisms can provide a reference for related processing application situations. In this study, an in-situ observation method with the multi-layer structure optical platform was developed to better understand the kernel fracture behavior. SEM images show that the starch structure distribution inside the endosperm layer could be divided into core, transition and outer layers. Meanwhile, kernel interior crack formation mechanism was revealed under quasi-static compression and verified from the perspective of fracture and structural mechanics. Typical kernel contact surface expansion behavior under compression conditions was analyzed. The results indicate that the compressive strength of glutinous kernel (56.3 MPa) larger than indica (48.1 MPa), and it was affected by kernel surface dimension and microscopic structure. The study aims to in-depth analysis fracture mechanism of brown rice kernel during the processing, providing a methodological reference for bio-material fracture.
摘要：
Mo, TiH(2), Al and graphite elemental powders were used as starting materials for the activation reaction sintering process, which was employed to fabricate porous Mo(2)TiAlC(2). The alteration of phase constitution, volume expansion, porosity, pore size and surface morphology of porous Mo(2)TiAlC(2) with sintering temperatures ranging from 700 °C to 1500 °C were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and pore size tester. Both the pore formation mechanism and activation reaction process at each temperature stage were investigated. The experimental results illustrate that the sintered discs of porous Mo(2)TiAlC(2) exhibit obvious volume expansion and pore structure change during the sintering process. Before 1300 °C, the volume expansion rate and porosity increase with the increment of temperature. However, with the sintering temperature above 1300 °C, the volume expansion rate and porosity decrease. At the final sintering temperature of 1500 °C, porous Mo(2)TiAlC(2) with a volume expansion rate of 35.74%, overall porosity of 47.1%, and uniform pore structure was synthesized. The pore-forming mechanism of porous Mo(2)TiAlC(2) is discussed, and the evolution of pressed pores, the removal of molding agents, the decomposition of TiH(2), and the Kirkendall effect caused by different diffusion rates of elements in the diffusion reaction are all accountable for the formation of pores.
通讯机构：
[Chen, Y ] W;Wuhan Polytech Univ, Sch Mech Engn, Wuhan, Peoples R China.
关键词：
fish head and tail;target detection;deep learning;contrast test;MobileNetv3
摘要：
The quality of fish pre-treatment processing directly affected the production competitiveness of the fish industry. The removal of heads and tails is one of the key technologies in the fish processing. This study proposed an identification method of fish head and tail, and the original YOLOV3 model was improved by replacing the backbone feature extraction network of the YOLOV3 model with the lightweight neural network MobileNetv3. Firstly, a freshwater fish image dataset was created and divided into the training, validation and test sets with the assigned ratio of 6:2:2. Next, the freshwater fish dataset was trained using the target detector YOLOV3. Finally, the average accuracy mAP (mean of Average Precision) and the average image detection time were used as the accuracy and speed indexes to evaluate the detection effect of the model. In addition, the SSD-MobileNetv3 and SSD-VGG16 were introduced into present study and they were compared with the improved algorithm. The experimental results showed that the detection speed of the YOLOV3 model with MobileNetV3 was significantly improved. The mAP of YOLOV3-MobileNetv3 model was 98.36%, the inference speed was 28.2 ms, which was 5.09%, 4.24% and 2.07% higher than the mAP of other three models (SSD-VGG16, SSD-MobileNetv3 and YOLOV3-Darknet-53), and the average detection time shortened by 86%, 9.99% and 29%, respectively. Therefore, this experimental method of head and tail of freshwater fish could achieve real-time detection and recognition of various kinds of freshwater fish, which had the great advantages of high detection accuracy and fast detection speed.
