关键词： Elastic moduli  

摘要： Through coarse-grained molecular dynamics simulations, the effects of nanoparticle properties, polymer-nanoparticle interactions, chain crosslinks and temperature on the stress-strain behavior and mechanical reinforcement of polymer nanocomposites (PNCs) are comprehensively investigated. By regulating the filler-polymer interaction (miscibility) in a wide range, an optimal dispersion state of nanoparticles is found at moderate interaction strength, while the mechanical properties of PNCs are improved monotonically with the increase of the particle-polymer interaction due to the tele-bridge structures of nanoparticlesviapolymer chains. Although smaller-sized fillers more easily build interconnected structures, the elastic moduli of PNCs at the percolation threshold concentration where a three-dimensional filler network forms are almost independent of nanoparticle size. Compared with spherical nanoparticles, anisotropic rod-like ones, especially with larger aspect ratio and rod stiffness, contribute exceptional reinforcement towards polymer materials. In addition, the elastic modulus with the strain, derived from the stress-strain curve, shows an analogous nonlinear behavior to the amplitude-dependence of the storage modulus (Payne effect). Such a behavior originates essentially from the failure/breakup of the microstructures contributing to the mechanical reinforcement, such as bound polymer layers around nanoparticles or nanoparticle networking structures. The Young's modulus as a function of the nanoparticle volume fraction greatly exceeds that predicted by the Einstein-Smallwood model and Guth-Gold model, which arises primarily from the contribution of the local/global filler network. The temperature dependence of the Young's modulus is further examined by mode coupling theory (MCT) and the Vogel-Fulcher-Tammann (VFT) equation, and the results indicate that the time-temperature superposition principle holds modestly above the critical temperature on the short-time

关键词： chlorpropamide   polymorphic interconversion   in situ mechanical Raman spectroscopy   tableting   deformation  

摘要： The objective of this study is to achieve a fundamental understanding of polymorphic interconversion during the tableting process, including during compaction, dwell, decompression/unloading, and ejection using an in situ mechanical Raman spectroscopy. The fit-forpurpose in situ mechanical Raman spectroscopy developed herein can provide simultaneous measurement of Raman spectra and densification for the powder compacts. Chlorpropamide (CPA), an antidiabetic drug, was selected as a model pharmaceutical compound because of its mechanical shear-induced polymorphic conversions. The results confirm that CPA polymorph A (CPA-A) was transformed to CPA polymorph C (CPA-C) under different compaction stresses. We also observed that the converted polymorph CPA-C could be reverted to the CPA-A due to the elastic recovery of powder compacts as detected during dwelling and unloading. This study is the first depiction of the dynamics of CPA polymorphic interconversion during compression, dwell, unloading, and ejection. Mechanistically, this study illustrates a correlation between the change in the powder compact's relative density and polymorphic interconversion of the drug substance in different solid-state forms. The present research suggests that the process-induced polymorph conversion is a complicated dynamic process, which could be affected by the compaction pressure, the elasticity/plasticity of the material, the level of elastic recovery, and the dissipation of residual stress. In summary, this study demonstrates that the in situ mechanical Raman spectroscopy approach enables the simultaneous detection of mechanical and chemical information of the powder compact throughout the tableting process.

关键词： 电池包   有限元   模态分析   挤压   机械冲击  

摘要： 电池包在整车行驶过程中会受到挤压和冲击载荷的作用,在产品设计开发阶段,基于正确的有限元仿真分析可以有效地考察电池包箱体和零部件是否满足机械性能要求。建立了电池包精细化有限元模型,通过对比电池包扫频实验和有限元模态分析结果,可以获得准确的有限元模型,并利用有限元仿真分析手段分别对电池包进行了两个水平方向的挤压和竖直方向机械冲击分析。

关键词： 七自由度冗余机械臂   动力学   ADAMS  

摘要： 针对七自由度冗余机械臂动力学建模正确性及动力学仿真问题,首先,基于Solid-Works建立七自由度冗余机械臂模型,采用牛顿-欧拉法建立机械臂动力学模型.然后,给定实际工况下的角速度并将机械臂模型导入ADAMS中,进行动力学仿真,得到机械臂各关节力矩随时间变化的曲线.最后,从动力学仿真轨迹中取一组瞬态关节角,将其角速度和角加速度带入动力学方程求出各关节力矩,对比理论计算与仿真结果并根据曲线分析机械臂动力学特性.仿真结果验证了动力学建模的正确性,同时得出机械臂运动时各关节力矩存在耦合影响,为机械臂的后续控制研究和轨迹规划提供了试验基础.

关键词： 材料成型及控制工程   能源与动力工程   机械制造及其自动化   机械电子工程   卓越工程师教育培养计划   国家特色专业   机械设计制造及其自动化   三峡大学  

摘要： 2014年1月原机械与材料学院更名为机械与动力学院,学院现设有机械设计制造及其自动化、机械电子工程、材料成型及控制工程、工业工程、能源与动力工程、核工程与核技术六个本科专业,其中机械设计制造及其自动化为国家特色专业、第二批卓越工程师教育培养计划专业和省本科品牌专业,材料成型及控制工程为第三批卓越工程师教育培养计划专业。

关键词： 机械臂   RV减速器   齿侧间隙   关节摩擦   动力学  

摘要： 为了探究减速器间隙及关节摩擦对医用机械臂动力学特性的影响,提高医用机械臂控制及摆位的精度,课题组以医用机械臂为对象,利用拉格朗日方程建立了包含RV减速器中心轮与行星轮之间的时变啮合刚度、啮合阻尼、齿侧间隙及关节铰接摩擦的动力学模型。仿真分析结果表明:由于时变啮合刚度、啮合阻尼、齿侧间隙的出现,医用机械臂角加速度出现非周期波动,且随着间隙的增加,波动幅值增大,而关节摩擦可以降低加速度波动的幅值,但会造成系统能量损失;同时,时变啮合刚度、啮合阻尼和齿侧间隙使医用机械臂末端在同一时刻到达位置出现偏差,运动出现时间上的延迟,关节摩擦使末端轨迹的误差进一步增加。

关键词： Bilayer film   Deformation   Mechanical properties   Interface   Molecular dynamics  

摘要： The deformation and mechanical properties of Cu/Ni bilayer films with and without an interfacial defect, void, or asperity under tensile and shear tests are studied using molecular dynamics simulations based on the manybody embedded-atom potential. These properties are investigated in terms of atomic trajectories, the dislocation extraction algorithm, common neighbor analysis, shear strain distribution, and the stress-strain curve. The simulation results show that during the tensile test, defect-free bilayer films have higher ultimate strength and strain than those of bilayer films with a void or asperity. The bilayer films with an interfacial void cause dislocation and crack nucleation at the void. For a given defect size, a void has more influence than that of an asperity on the ultimate stress and strain of bilayer films under tension. The presence of an asperity increases the shear deformation resistance of bilayer films.

关键词： 地电波   牛顿欧拉法   动力学   控制器  

摘要： 基于Simulink仿真研究了地电波检测机械臂的动力学建模、仿真和分析。针对动力学建模问题,采用牛顿-欧拉法将地电波检测机械臂的各连杆质量、质心位置、惯性张量、连杆长度等带入,得到了其逆动力学方程,然后将计算好的动力学方程改写成状态空间方程的形式。基于地电波检测机械臂动力学模型设计了控制器,并在Simulink环境下进行了仿真,达到了良好的控制效果,为接下来更先进的控制器设计打下了基础。

关键词： 动力分离器   聚丙烯装置   机械密封   改造   干气密封  

摘要： 聚丙烯装置A301动力分离器机械密封使用寿命短,严重影响装置的长周期运行。将动力分离器机械密封改造为干气密封,改造后,解决了动力分离器的密封故障问题,延长了装置的运行周期。