关键词： Molecular dynamics   Transition-state theory   Non-equilibrium structure   Thermophysical properties   Athermal thresholds  

摘要： The thermo-kinetic characteristics that dictate the activation of atomistic crystal defects significantly influence the mechanical properties of crystalline materials. Grain boundaries (GBs) primarily influence the plastic deformation of FCC metals through their interaction with mobile dislocation defects. The activation thresholds and atomic mechanisms that dictate the thermo-kinetic properties of grain boundaries have been difficult to study due to complex and highly variable GB structure. This paper presents a new approach for modelling GBs which is based on a systematic structural analysis of metastable and stable GBs. GB structural transformation accommodates defect interactions at the interface. The activation energy for such structural transformations was evaluated with nudged elastic band analysis of bi-crystals with several metastable 0 K grain boundary structures in pure FCC Aluminium (Al). The resultant activation energy was used to evaluate the thermal stability of the metastable grain boundary structures, with predictions of transition time based on transition state theory. The predictions are in very good agreement with the minimum time for irreversible structure transformation at 300 K obtained with molecular dynamics simulations. Analytical methods were used to evaluate the activation volume, which in turn was used to predict and explain the influence of stress and strain rate on the thermal and mechanical properties. Results of molecular dynamics simulations show that the GB structure is more closely related to the elastic strength at 0 K than the GB energy. Furthermore, the thermal instability of the GB structure directly influences the relationship between bi-crystal strength, temperature and strain rate. Hence, theoretically consistent models are established on the basis of activation criteria, and used to make predictions of temperature-dependent yield stress at a low strain rate, in agreement with experimental results. (C) 2016 Acta Materialia

关键词： Wave energy   Energy harvesting   Frequency up-converted   Impact  

摘要： This paper proposes a novel mechanical impact-driven frequency up-converted device for wave energy harvesting, which could bridge a gap between waves of frequency 0.03-1 Hz and electrical generators of operation frequency hundreds hertz. The device mainly consists of a cylindrical buoy, beams and teeth. A mathematical model for the dynamics of such a device is presented, which incorporates the fluid-structure interaction between the wave and the buoy, and the structural interactions between the beams and the teeth. The momentum balance method and the coefficient of restitution are employed, which give rise to piecewise nonlinear equations governing the motions of the buoy and the beams. Experimental tests carried out in a wave flume validate the model and prove the effectiveness of frequency up-converted method in wave energy harvesting. The characteristics of frequency up-converted transformation from buoy motion to beams oscillation for wave energy harvesting are probed, and the effects of beam Young's modulus, beam number, wave period and wave height on strain power of the beams are explored. (C) 2016 Elsevier Ltd. All rights reserved.

关键词： MOLECULAR dynamics   ORGANIC semiconductors   POISSON'S ratio   GLASS transition temperature   DODECYL phosphocholine  

摘要： The ability to predict the mechanical properties of organic semiconductors is of critical importance for roll-to-roll production and thermomechanical reliability of organic electronic devices. Here, we describe the use of coarse-grained molecular dynamics simulations to predict the density, tensile modulus, Poisson ratio, and glass transition temperature for poly(3-hexylthiophene) (P3HT) and its blend with C-60. In particular, we show that the resolution of the coarse-grained model has a strong effect on the predicted properties. We find that a one-site model, in which each 3-hexylthiophene unit is represented by one coarse-grained bead, predicts significantly inaccurate values of density and tensile modulus. In contrast, a three-site model, with one coarse-grained bead for the thiophene ring and two for the hexyl chain, predicts values that are very close to experimental measurements (density = 0.955 g cm-3, tensile modulus = 1.23 GPa, Poisson ratio = 0.35, and glass transition temperature = 290 K). The model also correctly predicts the strain-induced alignment of chains as well as the vitrification of P3HT by C-60 and the corresponding increase in the tensile modulus (tensile modulus = 1.92 GPa, glass transition temperature = 310 K). We also observe a decrease in the radius of gyration and the density of entanglements of the P3HT chains with the addition C-60 which may contribute to the experimentally noted brittleness of the composite material. Although extension of the model to poly(3-alkylthiophenes) (P3ATs) containing side chains longer than hexyl groups nonyl (N) and dodecyl (DD) groups correctly predicts the trend of decreasing modulus with increasing length of the side chain measured experimentally, obtaining absolute agreement for P3NT and P3DDT could not be accomplished by a straightforward extension of the three-site coarse-grained model, indicating limited transferability of such models. Nevertheless, the accurate values obtained for P3HT and P3HT:C-60

关键词： Fullerene- araldite LY 5052   Aradur HY 5052 epoxy resins   Thermo-mechanical properties   Molecular dynamics simulation  

摘要： A comparative study was conducted to determine the effects of fullerene on the thermo-mechanical properties of Araldite LY 5052/Aradur HY 5052 cross-linked resin epoxy by molecular dynamics simulations. Different from ordinary epoxy resins, Araldite LY 5052/Aradur HY 5052 cross-linked resin epoxy is composed of four compounds that provide different thermal and mechanical properties. The thermo-mechanical properties of three different Araldite LY 5052/Aradur HY 5052 cross-linked resin epoxies, of which one has no fullerene and two have weight fractions of 8.64% (LY/HY/C60 (1) epoxy system) and 15.9% (LY/HY/C60 (2) epoxy system), were comparatively studied. Simulation results indicated that the glass transition temperature (T-g) has slight variations for different fullerene-containing epoxy systems and that the coefficients of thermal expansions decrease by adding fullerene to the resin epoxy system. Furthermore, mechanical properties such as Young's, bulk, and shear moduli, as well as Poisson's ratio and density, show considerable improvements after the addition of fullerene to the epoxy systems. The best mechanical properties were obtained for the weight fractions of 8.64%;this result was in agreement with the experimental results. For example, the Young's modulus of the LY/HY epoxy system increases by 19.5% and 7.5% in the LY/HY/C60 (1) epoxy system and LY/HY/C60 (2) epoxy system, respectively. The evolution of the local structures of the different fullerene-containing epoxy systems were also investigated by studying the radial distribution functions. (C) 2016 Elsevier Ltd. All rights reserved.

关键词： PIMD集成技术   轨行机械   通用化设计   集成化设计  

摘要： 介绍了一种应用于轨行机械的新型集成技术—PIMD技术,阐述了集成设计理念和方法,运用有限元分析工具对设计结构进行了多方面分析。展示了PIMD技术的先进性以及在轨行机械行业广阔的应用前景。

关键词： 六自由度   柔性关节   动力学   拉格朗日方程   神经网络反演法  

摘要： 大多数的机器人都是在刚体动力学假设的基础上进行运动控制设计的,因此其在实际操作中的精度和效率受到一定的限制,而柔性机械臂可以很好地解决此类问题。首先给出了六自由度的柔性关节机械臂的简化模型,利用拉格朗日方法建立其动力学方程;然后以单自由度柔性关节机械臂为例,基于神经网络反演法对其控制率进行了设计;最后基于Simulink验证了控制器设计的有效性。

关键词： Polypropylene   Carbon fiber   Graphene   Molecular dynamics   Interfacial strength  

摘要： This study investigates the interfacial strengths between polypropylene (PP)/carbon fiber (CF) composites through experimental observation as well as using molecular dynamics (MD) simulation to determine optimal chemical functionalization groups for four PP/CF composites. First, the structures of PP/CF, PP-graft-maleic anhydride (PP-MAH)/CF, PP-MAH/CF-NH2 (2%) and PP-MAH/CF-NH2 (5%) were constructed to obtain stable interface structures by the simulated-annealing procedure, and these structures were further used to evaluate the interface bonding strength. The study found that the degrees of crystallinity of PP and PP-MAH at the interfaces are significantly improved when compared to those of the pristine structure. The results show, through the interaction energy per unit area and the tensile simulation mechanical strength, that the strengths of the modified PP/functionalized-CF are higher. Finally, the MD simulation results of the modified PP and functionalized-CF composites are demonstrated to provide an economical and quick approach to examine the mechanical properties of a polymer composite system before conducting an experiment. Such MD results can be utilized to guide both the design of polymer/carbon fiber composites and to select proper functionalized groups. (C) 2015 Elsevier B.V. All rights reserved.

关键词： 动力机械   减震设计   性能预测  

摘要： 减震技术在动力机械中的应用能够减少机械的磨损,增加机械的使用寿命。由于科学技术的不断进步,隔振技术也出现了很大的发展,原有的单层隔振技术已经提高为双层隔振,甚至出现了浮筏隔振技术。本文研发可以进行隔振、吸振计算的软件,目的是准确预测船舶动力机械的减振设计是否合理,是否能产生良好的减振效果。

关键词： 工程机械   橡胶悬置   MOONEY-RIVILIN   静刚度  

摘要： 以某挖掘机动力总成的橡胶悬置为对象,运用abaqus软件建立其有限元模型。基于橡胶标准样片单轴拉伸试验数据,通过数据拟合得到橡胶材料本构模型MOONEY-RIVILIN性能常数C10和C01,并完成了悬置CAE仿真分析。通过静刚度仿真与试验与对比,仿真结果与试验偏差在5%之内,CAE分析仿真可信。该仿真方法可为悬置结构优化提供设计依据。