关键词： 机械臂   ADAMS仿真   运动空间   动力学分析  

摘要： 以架管机的三自由度机械臂为研究对象,建立了架管机三维模型以及D-H坐标系,求解得到了机械臂末端位置的运动空间;用ADAMS软件分析了架管机机械臂不同负载下的运动,得到相关曲线。结果表明:机械臂Z轴运动空间的最大值为2.6 m,可以满足淮南地区的实际架管需求;架管机小臂Z轴的最大质心速度为2 m/s,在周期内会产生不稳定速度波动;速度、加速度曲线变化趋势相吻合,θ_(2)、θ_(3)的最大值分别是120°和58°,其仿真结果为架管机实际模型的搭建奠定了基础。

关键词： Cu-Fe interface   Mechanical property   Dislocation evolution   Molecular dynamic simulation  

摘要： Molecular dynamics simulations have been conducted to find out the cohesion property, tensile strength, and ( ) dislocation evolution of several Cu-Fe interfaces. It is found that Cu 111 /Fe(110)-KS and Cu(111)/Fe(110)-NW interfaces are not only energetically favorable with lower interface energies, but also have higher strength than Cu-Fe interfaces with other interface orientations. Simulations also reveal that the formation of Cu-Fe interfaces has an important effect to increase the tensile strength of Cu under tensile loading along the directions parallel to the interface due to the block of the dislocation movement by the interface. On the contrary, the tensile strength of the Cu-Fe interfaces is smaller than that of Cu along the direction perpendicular to the interface as a result of the weak interface cohesion. The simulated results are in good agreement with experimental observations in the literature, and could provide a deep understanding of mechanical property and dislocation evolution of Cu-Fe interfaces.

关键词： 热能与动力   制造工艺学   教学讨论   课程思政  

摘要： 热能与动力机械制造工艺学课程内容与工业、科技与经济发展密切相关。当前,我国正从制造业大国向制造强国迈进,亟需培养高质量的人才为国家建设贡献力量。本文结合多年教学经验,针对课程教学困境,提出解决方案。通过教学改革与课程思政,能有效激发学生爱国热情,增加学习兴趣,增强学习动力,促进他们今后在工作中充分发挥自身才能,更好地为实现中华民族伟大复兴而奋斗。

关键词： PLGA   beta-TCP   Mechanical characteristics   In vitro degradation   Kinetics  

摘要： The interference screw made of bioabsorbable polymers has been widely used in bone tissue engineering. Among the various ranges of polymer materials, the composite of polylactic glycolic acid (PLGA) and beta-tricalcium phosphate (beta-TCP) exerts high performance of biocompatibility and bioabsorption for the knee fixation and reconstruction surgery. The purpose of this research is to first investigate the influence of screw thread geometry on the mechanical properties of the biocomposites interference screw made of PLGA/beta-TCP composite. Three biocomposite interference screws with different thread designs were compared in terms of the maximum insertion torque and pullout force via numerical analysis. It was found that the thread design with modified pitch failed to improve the ease of insertion into the bone tunnel and resistance of removal. Although the modified thread angle type enhanced the pull-out strength, the higher insertion torque and strain energy density (SED) exerted on the bone made it was easy to break during the insertion process and enlarge the bone tunnel. Then, based on the optimal design of the screw, in-vitro degradation experiment over 26 weeks was conducted to investigate the degradation kinetics and evaluate the mechanical properties of the PLGA/beta-TCP interference screw. The in vitro degradation analysis revealed that the molecular weight residual rate and degradation time presented a linear negative correlation within 0 to 16 weeks and the degradation rate was significantly accelerated after 16 weeks. However, it didn't exhibit any differences in mass loss with the degradation time, which indicated that the material can still keep the shape in half a year. In other words, the interference screw made of PLGA/beta-TCP composite can meet the requirements of clinical use and has a certain degree of safety. (C) 2020 Elsevier Ltd. All rights reserved.

关键词： Dielectric elastomers   ANCF   Flexible multibody systems   Generalized-alpha algorithm   Electrically-driven dynamics  

摘要： A computation methodology for studying the dynamics of flexible mechanical systems containing soft actuators of dielectric elastomers is originally proposed. The absolute nodal coordinate formulation (ANCF) is used to describe the rigid-body motions and large deformations of the flexible mechanical systems. A new viscoelastic solid element of ANCF is proposed for meshing the components of dielectric elastomers. The constitutive model of dielectric elastomers is deduced from the Helmholtz free energy according to thermodynamics, and embedded into the ANCF solid element. The proposed solid element is an 8-node hexahedra element with each node represented by 12 spatial nodal coordinates and 4 electrical nodal coordinates. Both the displacement and electric fields of the continuum system are discretized and described by the proposed element with high-order functions of interpolation. The element internal forces and their Jacobians are derived. Then dynamic equations of flexible multibody systems containing components of dielectric elastomers are established and solved numerically via the generalized-alpha algorithm of time integration. Finally, numerical examples are given to validate the proposed element and the computation methodology. The experimental test is also performed, and the test results are compared with the numerical results to further validate the proposed methodology. (C) 2020 Elsevier Ltd. All rights reserved.

关键词： Solid electrolyte interphase   Molecular dynamics simulations   Li-ion battery   Conductivity  

摘要： The influence of different amounts of Mn2+ contaminants on mechanical, dynamical, and structural properties of a solid electrolyte interphase (SEI) has been studied using atomistic molecular dynamics and Monte-Carlo simulations employing the many-body polarizable APPLE&P force field. Bulk SEI systems comprised of amorphous Li2CO3 with some fraction of cations replaced with Mn2+ ions have been investigated over a wide temperature range. Replacement of 5, 10, or 20% of positive charges with Mn2+ ions resulted in 3, 6, or 11% increase in density and leading to approximately a 20, 50, or 100 K increase in the glass transition temperature (T-g), respectively. Cations and anions showed similar dynamics at high temperatures, however at temperatures approaching T-g the CO32- and Mn2+ ions showed an expected divergent slowing down in dynamics therefore forming a glassy matrix in which Li+ ions continued to show significant movements, i.e. Li+ dynamics showed a decoupling from the dynamics of other ions. The Li+ conductivity values on the order of 10(-6) S/cm have been observed for all concentrations at room temperature. Addition of Mn2+ ions also resulted in an increase of the shear modulus leading to values higher than 8 GPa at room temperature, which is high enough to potentially suppress the Li metal dendrite growth.

关键词： Stress   Deformation   Chemical structure   Optimization   Carbon nanotubes  

摘要： Coiled carbon nanotubes (CCNTs) have increasingly become a vital factor in the new generation of nanodevices and energy-absorbing materials due to their outstanding properties. Here, the multiobjective optimization of CCNTs is applied to assess their mechanical properties. The best trade-off between conflicting mechanical properties (e.g., yield stress and yield strain) is demonstrated and the optimization of the geometry enables us to find the astonishing CCNTs with a stretchability of 400%. These structures have been recognized for the first time in the field. We derived several highly accurate analytical equations for the yield stress and yield strain by the implementation of multiobjective optimization and fitting a theoretical model to the results of molecular dynamics (MD) simulations. The optimized structures are highly resilient because of two distinct deformation mechanisms depending on the dimensions of CCNTs. For small CCNTs, extraordinary extensibility is mainly contributed by buckling and nanohinge-like deformation with maintaining the inner coil diameter. On the other hand, for large CCNTs, this is accomplished by the creation of a straight CNT-like structure in the inner-edge of the CCNT with a helical graphene ribbon twisted around it. Our work represents an important advance in the design of CCNT based mechanical nanodevices.

关键词： Nanocomposites   Molecular dynamics   Interfacial structures and mechanics  

摘要： The interfacial mechanism has always been a concern for silica reinforced rubber nanocomposites, which are widely used in green tires. In this work, the relationship between the structures and mechanical properties at the interface of silica/SBR was investigated via all-atom molecular dynamics simulation. The results illustrated that different grafting fractions of the KH550 influence the inter-and intramolecular interactions between SBR/silica, which affects the amount of adsorbed chains on the filler surface, the number and length of trains, loops and tails, the flexibility of the bulk and the mechanical behavior of the interfacial deformation. Especially, the introduction of the chemical bonding increases the interfacial tensile strength to 760 MPa at 300K, which is 4 times that of the system without any modifications. Meanwhile, the chemical bonding reduces the differences of the structure between the interface and the bulk, together with the anisotropy of the system.

关键词： Liquid crystalline elastomer   Grafted nanoparticles   Nanocomposites   Interface  

摘要： Synthesizing surface-grafted Au nanoparticles (grafted-AuNPs) for incorporation into a liquid crystalline elastomer (LCE) matrix yields high contents of nanoparticles that are chemically compatible and soluble in the matrix. To investigate the change in the internal microstructure by inserting grafted-AuNPs and the mechanical role of the interfaces in the LCE/Au nanocomposites, all-atom molecular dynamics simulations were conducted. The results suggest that the insertion of the grafted-AuNP disrupts the LCE mesogen arrangement, especially in the interfacial area. Additionally, the strain energy density distributed to each molecular component revealed that the grafted unit on the side of the LCE matrix forms a highly entangled network with a semi-rigid microstructure and enables high load transfer efficiency. By contrast, a ductile grafted layer formed on the side of the AuNP surface acts as a cushion, which allows the AuNP to exist in the unloading state. Furthermore, the curvature of the inserted AuNPs is crucial in changing the mechanical and structural properties of the LCE matrix phase.

关键词： Cells  

摘要： How does a cell self-organize so that its appendages attain specific lengths that are convenient for their respective functions? What kind of 'rulers' does a cell use to measure the length of these appendages? How does a cell transport structure building materials between the cell body and distal tips of these appendages so as to regulate their dynamic lengths during various stages of its lifetime? Some of these questions are addressed here in the context of a specific cell appendage called flagellum (also called cilium). A "time of flight" (ToF) mechanism, adapted from the pioneering idea of Galileo, has been used successfully very recently to explain the length control of flagella by a biflagellate green algae. Using the same ToF mechanism, here we develop a stochastic model for the dynamics of flagella in two different types of monoflagellate unicellular organisms. A unique feature of these monoflagellates is that these become transiently multi-flagellated during a short span of their life time. The mean length of the flagella in our model reproduce the trend of their temporal variation observed in experiments. Moreover, for probing the intracellular molecular communication between the dynamic flagella of a given cell, we have computed the correlation in the fluctuations of their lengths during the multiflagellated stage of the cell cycle by Monte Carlo simulation. (C) 2020 Elsevier B.V. All rights reserved.