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Impact of Carbon Chain Structures in the Backbone on the Flexibility of Modified Polyarylene Sulfide Resins: Molecular Dynamics Simulations and Mesoscopic Analysis

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Chinese Journal of Polymer Science 2024年第4期42卷 544-557页

作者： Chi Zhang Rong liu Jing-Yuan liu Wen-Wei Jiang Key Laboratory of Fine Chemical engineering and Functional Materials School of Chemical EngineeringSichuan UniversityChengdu610065China

In the domain of high-performance engineering polymers, the enhancement of mechanical flexibility in poly(phenylene sulfide) (PPS) resins has long posed a significant challenge. A novel molecular structure, designated as PP-He-IS, wherein imide rings and an aliphatic hexylene chain are covalently incorporated into the PPS backbone to enhance its flexibility, is introduced in this study. Molecular dynamics (MD) simulations are employed to systematically explore the effects of diversifying the backbone chain structures by substituting phenyl units with alkyl chains of varying lengths, referred to as PP-A-IS where “A” signifies the distinct intermediary alkyl chain configurations. Computational analyses reveal a discernable decrement in the glass transition temperature (Tg) and elastic modulus, counterbalanced by an increment in yield strength as the alkyl chain length is extended. Notably, the PP-He-IS variant is shown to exhibit superior yield strength while simultaneously maintaining reduced elastic modulus and Tg values, positioning it as an advantageous candidate for flexible PPS applications. Mesoscopic analyses further indicate that structures such as PP-He-IS, PP-Pe-IS, and PP-Bu-IS manifest remarkable flexibility, attributable to the presence of freely rotatable carbon-carbon single bonds. Experimental validation confirms that a melting temperature of 504 K which is lower than that of conventional PPS, and lower crystallinity are exhibited by PP-He-IS, thereby affording enhanced processability without compromising inherent thermal stability. Novel insights into the strategic modification of PPS for mechanical flexibility are thus furnished by this study, which also accentuates the pivotal role played by molecular dynamics simulations in spearheading high-throughput investigations in polymer material modifications.

关键词： Molecular dynamics simulations Polyarylene Sulfide Main-chain modifications Flexibility Aliphatic hexylene chain

Effects of seepage pressure on the mechanical behaviors and microstructure of sandstone

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Journal of Rock Mechanics and Geotechnical engineering 2024年第6期16卷 2033-2051页

作者： Xuewei liu Juxiang Chen Bin liu Sai Wang Quansheng liu Jin Luo State Key Laboratory of Geomechanics and Geotechnical engineering Institute of Rock and Soil MechanicsChinese Academy of SciencesWuhan430071China Faculty of engineering China University of GeosciencesWuhan430074China Key Laboratory of Safety for Geotechnical and Structural engineering of Hubei Province School of Civil EngineeringWuhan UniversityWuhan430072China

Surrounding rocks of underground engineering are subjected to long-term seepage pressure,which can deteriorate the mechanical properties and cause serious *** order to understand the impact of seepage pressure on the mechanical property of sandstone,uniaxial compression tests,P-wave velocity measurements,and nuclear magnetic resonance(NMR)tests were conducted on saturated sandstone samples with varied seepage pressures(i.e.0 MPa,3 MPa,4 MPa,5 MPa,6 MPa,7 MPa).The results demonstrate that the mechanical parameters(uniaxial compressive strength,peak strain,elastic modulus,and brittleness index),total energy,elastic strain energy,as well as elastic strain energy ratio,decrease with increasing seepage pressure,while the dissipation energy and dissipation energy ratio ***,as seepage pressure increases,the micro-pores gradually transform into meso-pores and *** increases the cumulative porosity of sandstone and decreases P-wave *** numerical results indicate that as seepage pressure rises,the number of tensile cracks increases progressively,the angle range of microcracks is basically from 50-120to 80-100,and as a result,the failure mode transforms to the tensile-shear mixed failure ***,the effects of seepage pressure on mechanical properties were *** results show that decrease in the effective stress and cohesion under the action of seepage pressure could lead to deterioration of strength behaviors of sandstone.

关键词： Rock mechanics mechanical property Seepage pressure Numerical simulation Microcracks

mechanical Properties and Microstructure of the Shear Band Formed at Cryogenic Temperature in the NiCrFe Medium‑Entropy Alloy

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Acta Metallurgica Sinica(English Letters) 2024年第8期37卷 1377-1386页

作者： Ruoyu liu Wenshu Li Xiayang Yu Lanyi liu Bingfeng Wang school of Materials Science and engineering Central South UniversityChangsha 410083China State Key Laboratory of Powder Metallurgy Central South UniversityChangsha 410083China

There are nanotwins in the shear band formed in a moment(about 10^(−5)s)in some NiCrFe-based medium-entropy alloys(MEAs),and these shear bands can be recognized as a special kind of materials due to their high strength and good *** this study,the single shear band of the NiCrFe MEA was prepared at 77 K.A series of characterizations were carried out to analyze the microstructures in the shear *** strength of the shear band was investigated by the split Hopkinson pressure bar and in-situ *** micropillar in the shear band containing nanotwins exhibits excellent strengthplasticity *** compressive yield strength of the shear band measured by in-situ compression is 175%higher than that of the matrix,reaching 1405 MPa,with the fracture strain exceeding *** strengthening mechanism of the shear band was revealed by the combination of the experimental results and molecular dynamics *** synergistic effect of multiple strengthening mechanisms enhances the strength of the NiCrFe MEA containing nanotwins,in which the grain boundary strengthening of the ultrafine equiaxed grains and the dynamic Hall–Petch effect of the nanotwins *** addition,the good plasticity of the shear band is ascribed to the stress concentration reduction of the twin boundaries of nanotwins and the activation of multiple slip systems due to the randomly oriented *** findings provide theoretical guidance for the design of nanotwinned MEAs to realize excellent strength-plasticity synergy for structural materials.

关键词： Medium-entropy alloy Shear band Nanotwins Strengthening mechanism

Experimental investigation of junction growth of rough contacts using X-ray computed tomography

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Friction 2024年第11期12卷 2519-2531页

作者： Runliang WANG Jianhua liu Bo liu Duo JIA Xiaoyu DING school of mechanical engineering Beijing Institute of TechnologyBeijing 100081China AECC Shenyang Engine Research Institution Shenyang 110000China

The real contact area(RCA)of randomly rough contacts has received a great deal of attention because it correlates strongly with friction,lubrication,sealing,and *** have revealed that the RCA associated with deterministic normal squeezing loads increases when tangential loads are also applied,in a phenomenon called junction ***,experimental investigations of the junction growth of randomly rough contacts are ***,we used X-ray computed tomography(CT)to measure junction growth when two aluminum alloy surfaces were in contact.A high-resolution experimental setup was used to apply loads and observe contact behaviors at a resolution of 4μ*** RCA and average contact gaps were computed using a three-dimensional(3D)geometric model constructed from gray CT images using the Otsu thresholding *** results showed that the RCA increased as the normal load *** RCA increased by 22.67%after a tangential load was applied(junction growth),and the average gap decreased by 14.01%after a tangential load was ***,X-ray CT accurately measured the junction growth as a novel quantitative method.

关键词： three-dimensional(3D)contact analyses real contact area(RCA),junction growth X-ray computed tomography(CT) assembly interfaces

Effect of Pre-strain on Microstructure and Stamping Performance of High-strength Low-alloy Steel

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Journal of Wuhan University of Technology(Materials Science) 2024年第3期39卷 774-780页

作者：刘坡 WEN Zhicheng liu Zheng 许峰 school of mechanical engineering Guilin University of Aerospace TechnologyGuilin 541004China school of Automotive Engineer-ing Changshu Institute of TechnologyChangshu 215500China

In this study,pre-strain ranging from 0 to 0.12 was applied through uniaxial tension on high-strength low-alloy(HSLA)specimens with four kinds of grain *** of pre-strain and grain size on me-chanical property was investigated through tensile *** of the pre-strained and tensile tested samples were analyzed,*** 30.8°v-bending and following flattening,as well as Erichson cupping tests,were performed on the pre-strained *** show the elongation ratio of grain and dislocation density increases with *** platform is removed when pre-strain is larger than 0.06 while yielding plateau period decreases with pre-strain less than 0.06 due to reduction of pinning *** 30.8°v-bending and the following flattening tests are successfully accomplished on all the pre-strained samples with different grain *** in grain size,along with increase in pre-strain,causes increase in strength and decrease in elongation rate as well as cupping ***-strain causes very slight effect on bending ability,much less than that on mechanical property and cupping test *** impact of the pre-strain and grain size on HSLA steel deformability is inconspicuous.

关键词： strain hardening dislocation texture bending erichson cupping test

Design and performance investigation of modified dual reflector parabolic trough collector with double planar mirrors

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Science China(Technological Sciences) 2024年第3期67卷 902-918页

作者： LI Peijing liu TaiXiu QIN YuanLong LI JiChao liu QiBin school of Energy Powerand Mechanical EngineeringNorth China Electric Power University Beijing 226China Institute of engineering Thermophysics Chinese Academy of SciencesBeijing 100190China University of Chinese Academy of Sciences Beijing 100049China Department of Thermal Science and Energy engineering University of Science and Technology of ChinaHefei 230027China

In a typical parabolic trough collector(PTC), sunlight is concentrated at the bottom of the absorber tube. This concentrated solar flux leads to uneven heat distribution, resulting in high local temperatures and significant thermal stress on the absorber *** limitations have restricted the application of PTCs in solar thermochemistry and other fields and have impacted their safe operation. In this study, a new PTC with dual planar mirrors(DPMS) is proposed to homogenize the circumferential solar flux distribution of the absorber tube. A design method and single-objective optimization of the new PTC with a DPMS are proposed,and an uncertainty analysis of the operational and structural parameters is performed. A coupled light-heat-structure numerical model was developed to study the heat transfer performance and structural mechanical properties. The thermodynamic properties of the PTC with DPMS under different boundary conditions were analyzed. The results show that the circumferential temperature difference of the new PTC is within 2.6 K, and the circumferential thermal deformation is within 0.9 mm under typical working conditions(the inlet velocity of the heat transfer fluid is 3 m/s, inlet temperature is 573.15 K, and the direct normal irradiance is 1000 W/m^(2)). Compared with conventional PTCs, the circumferential temperature difference is reduced by 74%–90%, and the maximum thermal deformation along the y-axis is reduced by more than 95% under all working conditions(1–5 m/s, 373.5–675.15 K, 200–1000 W/m^(2)). The new PTC maintains the uniformity of the circumferential solar flux distribution for different operating parameters(sun incident angle of 0°–3°) and installation errors(±3 mm), is suitable for solar energy applications in various fields, and has the potential for large-scale applications.

关键词： solar thermal energy parabolic trough collector secondary reflector solar flux distribution optical optimization

Surrounding rock pressure in the tunnel portal section through moraine under freeze-thaw action

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Journal of Mountain Science 2024年第7期21卷 2480-2493页

作者： CHEN Zhimin liu Baoli liu Yaohui XU Jiangtao school of Civil engineering Lanzhou Jiaotong UniversityLanzhou 730070China CSCEC AECOM Consultants Co. ltdLanzhou 730000China National and Local Joint engineering Laboratory of Road and Bridge engineering Disaster Prevention Technology Lanzhou Jiaotong UniversityLanzhou 730070China

Moraines,characterized by the accumulation of rock and soil debris transported by glacial activity,present unique challenges for tunnel construction,particularly in portal sections,due to prevailing geographical and climatic conditions that facilitate freeze-thaw *** these challenges,there is a dearth of studies investigating the influence of freeze-thaw action and water content on the mechanical properties of moraines,and no research on calculating surrounding rock pressure in moraine tunnels subjected to freeze-thaw *** this study,direct shear tests under freeze-thaw cycles were conducted to examine the effects of freeze-thaw cycles and water content on the mechanical properties of frozen moraine.A comprehensive parameter K,integrating the number of freeze-thaws and water content,was introduced to model cohesion *** on Terzaghi Theory,we propose an improved algorithm for calculating surrounding rock pressure at the portal section of moraine *** a tunnel as a case study,surrounding rock pressure was calculated under various conditions to validate the Improved Algorithm's *** results show that:(1)Strength loss exhibits a linear trend with the number of freeze-thaw cycles at water content levels of 4%and 8%,while at 12%water content,previous freeze-thaw cycles induce more significant damage to the soil.(2)Moraine saturation peaks between 8%and 12%water *** repeated freeze-thaw cycles,moraine shear strength initially increases before decreasing with varying water content.(3)The internal friction angle of moraine experiences slight reductions with prolonged freeze-thaw cycles,but both freeze-thaw cycles and water content significantly influence cohesion.(4)Vertical surrounding rock pressure increases after the initial freeze-thaw cycle,particularly with higher water content,although freeze-thaw cycles have minimal effect on it.(5)Freeze-thaw cycles lead to a substantial increase in lateral surrounding rock pre

关键词： Moraines Freeze-thaw cycles Direct shear test Surrounding rock pressure

Hybrid 3D printed three-axis force sensor aided by machine learning decoupling

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International Journal of Smart and Nano Materials 2024年第2期15卷 261-278页

作者： Guotao liu Peishi Yu Yin Tao Tao liu Hezun liu Junhua Zhao Jiangnan Key Laboratory of Advanced Food Manufacturing Equipment and Technology School of Mechanical EngineeringJiangnan UniversityWuxiPR China Jiangsu Province engineering Research Center of Micro-Nano Additive and Subtractive Manufacturing Institute of Advanced TechnologyJiangnan UniversityWuxiPR China

Identification of magnitude and orientation for spatially applied loading is highly desired in the fields of not only the machinery components but also human-machine *** the fact that the 3-axis force sensor with different structures has been proposed to measure the spatial force,there are still some common limitations including the multi-step manufacturing-assembly processes and complicated testing of decoupling ***,we propose a rapid fabrication strategy with low-cost to achieve high-precision 3-axis force *** sensor is designed to compose of structural Maltese cross base and sensing *** is directly fabricated within one step by a hybrid 3D printing technology combining deposition modeling(FDM)with direct-ink-writing(DIW).In particular,a machine learning(ML)model is used to convert the strain signal to the force *** of a mount of calibration tests,this ML model is trained by sufficient simulation data based on programmed batch finite element *** sensor is capable of continuously identifying a spatial force with varying magnitude and orientation,which successfully quantify the applied force of traditional Chinese medicine physiotherapy including Gua Sha and *** work provides insight for design and rapid fabrication of multi-axis force sensors,as well as potential applications.

关键词： Hybrid 3D printing 3-axis force sensor machine learning nonlinear decoupling

STUDY ON SINGULAR CONFIGURATIONS AND COMPUTER SIMULATION OF 6R ROBOT

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Chinese Journal of mechanical engineering 2004年第2期17卷 177-180页

作者： Zhang Kai Hu Dejin liu Chengliang school of mechanical engineering,Shanghai Jiaotong University,Shanghai 200030, China school of mechanical engineering Shanghai Jiaotong University 上海 200030

When robot is at singular configuration, the limited hand velocity wouldrequire some joints with infeasible speeds so as to lead unsafely of the system. A method of solvingthe approximate velocity of joint near singular configuration point by adding damped vector isproposed and a modified algorithm is provided. With the analysis of J^(-1) the singularconfigurations of 6R robot are divided into structure boundary singularity , boundary singularity ,inner singularity and wrist singularity. The conditions of singularities of the robot have beenascertained. The computer simulations of the singularities of the robot are developed, which havemany advantages over previous description methods of the singular configurations of robot. With thehelp of boundary singularity analysis, a application in welding trajectory planning checking of therobot has been carried out and the simulation result proved visualized and useful.

关键词： Robot Singular configuration Computer simulation