关键词： TO2-SiO2 hybrid nanoparticle   Response surface methodology   Mechanical properties   Molecular dynamics simulation  

摘要： In this research, experimental and theoretical method are used to improve and optimized the thermo-mechanical properties of hybrid Epoxy/TiO2/SiO2 nano-Composites. For investigation of the influence of weight percentage of Silica toward Titana in TiO2-SiO2 hybrid nanoparticles on tensile properties of epoxy, the composite was optimized by surface methodology. Thirteen experiments were designed by using design expert commercial software totally. The TiO2-SiO2 hybrid nanoparticles were synthesized by sol-gel method. Then, epoxy/TiO2-SiO2 nanocomposites were prepared by direct mixing method. Four factors as elongation at break (EAB), yield strength (sigma y), ultimate strength (sigma u) and elastic modulus (E) were investigated by using tensile test device. The optimization results showed that the best (EAB), (sigma y), (sigma u) and (E) outcomes are 29.3, 17.72, 17.43 and 4.34% respectively with 14.64% weight percent of Silica in total amount of TiO2-SiO2 0.73% hybrid nanoparticles. In order to investigate the chemical and thermo-mechanical properties of nanocomposite as tensile tests, TGA, XRD, FT-IR, SEM, EDX and DRS analysis were performed. In addition, due to the high reliability in predicting the reaction among different materials and comparing with the results of experimental work, which is based on polymer-nanoparticle interaction energy, molecular dynamics simulation (MD) were used. The simulations were performed by using materials studio (MS) software. The numerical and analytical results show that the presence of small amount of Silica beside Titanium creates a strong interaction between fillers and epoxy resin.

关键词： electro-responsive materials   multiphysics   polyampholytes   smart materials   stimuli-responsive polymers  

摘要： Multifunctionality in polymers facilitates their application in emerging technologies. Electrical fields are a preferred stimulus because of the speed and ease of application to bulk polymers. While a wide range of electrically triggered actuators are developed, and electrically controlled adhesion between gels is demonstrated, modification of bulk mechanical properties via electrical stimuli remains elusive. Polymers with covalently incorporated ionic charge (polyelectrolytes) should be well suited to achieving this goal since the mechanical properties depend on electrostatic interactions and these charges are intrinsically susceptible to electric fields. Molecular dynamics simulations are utilized here to investigate whether electric fields can modulate the mechanical properties of polyelectrolytes and to understand the governing mechanisms. Mechanical property modulation by electric field is found to be sensitive to the charge distribution-charges must be tightly attached to the polymer backbone, and responsivity is greater if a single backbone contains both positive and negative charges. The dominant mechanisms are reorientation and stretching of the polymer chains, which also elongate the ionic clusters to maintain strong electrostatic interactions throughout deformation. These insights are critical for future experimental realization of polymers with electric field regulated mechanical properties.

关键词： mechanical seal   gap   microgrooves   two-phase flow   pressure distribution   leakage   deformations  

摘要： This paper presents the numerical methods for calculating the hydrodynamic characteristics of a mechanical seal, taking into account the possibility of a phase transition in its gap. In the numerical model, the solutions are used for the flow of both liquid and gas in the microgap of compaction obtained using the finite volume method. Regularities of the influence of the size and taper of the gap, the depth of the microgrooves, the pressure drop and the value of the saturated vapor pressure on the hydrodynamic characteristics of the seal are revealed. A method has been developed for calculating leaks, the stiffness of the lubricant layer, and the friction power in the seal gap, taking into account vaporization and thermal deformations of the sealing rings. Recommendations for the selection of the geometric parameters of the seal are offered. The cause of pulsating seal leakage has been identified. The developed technique is applicable both for cryogenic liquids and for water.

关键词： Thermo-mechanical   Microbeam   Two-dimensional functionally graded   Vibration   Moving load  

摘要： Due to the multi-functional requirements, more and more multi-dimensional functionally graded structures are reported, while their thermo-mechanical performances are still unclear. This paper aims at theoretically examining the thermo-mechanical behaviors of two-dimensional functionally graded (2D-FG) microbeam excited by a moving load. The formulation is established in the framework of the modified couple stress theory in combination with Hamilton's principle, and this problem is numerically solved through the finite element method (FEM). The material properties of the 2D-FG microbeam are treated as temperature-dependent parameters that vary smoothly along with both the axial and thickness directions, and three different thermal loads including the uniform, linear, and nonlinear temperature rises are taken into account. Both the fundamental frequency and the dynamic transverse deflection are analyzed with consideration of different axial and thickness gradient indexes, thermal load types, temperature rise amplitudes, and small scale parameters. The conclusion obtained in this paper can serve as a guideline for assessing the thermal performance of microstructures subjected to a moving load.

关键词： Azo dye   Providencia rettgeri   Cosubstrate   Whole-genome sequencing   Biodegradation mechanism  

摘要： Azo dyes pose hazards to ecosystems and human health and the cosubstrate strategy has become the focus for the bioremediation of azo dyes. Herein, Brilliant Crocein (BC), a model pollutant, was biodegraded by Providencia rettgeri domesticated from activated sludge. Additional ethanol, as a cosubstrate, could accelerate P. rettgeri growth and BC biodegradation, as reflected by the Gompertz models. This phenomenon was attributed to the smaller metabolites and greater number of potential pathways observed under the synergistic effect of ethanol. Genomic analysis of P. rettgeri showed that functional genes related to azo bond cleavage, redox reactions, ring opening and hydrolysis played crucial roles in azo dye biodegradation. Furthermore, the mechanism proposed was that ethanol might stimulate the production of additional reducing power via the expression of related genes, leading to the cleavage of azo bonds and aromatic rings. However, biodegradation without ethanol could only partly cleave the azo bonds.

关键词： adhesion   interfaces   mechanical properties   molecular dynamics   Nanocomposites  

摘要： Molecular dynamics (MD) simulations were adopted to compare the enhanced mechanical and tribological properties of nitrile rubber composites reinforced by different functionalized graphene sheets. Functional groups such as hydroxyl (-OH), carboxyl (-COOH), and ester (-COOCH3) were adopted. The constant strain method was applied to measure the mechanical properties of graphene/nitrile rubber composites. Sandwiched molecular models were developed to investigate the tribological properties of graphene/nitrile rubber composites by applying a shear load. The MD simulation results showed that the incorporation of functionalized graphene enhanced the Young's modulus, bulk modulus, and shear modulus of the nitrile rubber matrix. In addition, the coefficient of friction and abrasion rate of the functionalized graphene/nitrile rubber composites decreased. The mechanisms for the interfacial interactions between the functionalized graphene and nitrile rubber matrix were determined by calculating the mean square displacement of rubber chains, binding energy, and the radial distribution function between functional groups and polar atoms in the rubber matrix, respectively. The results of the atomistic simulations indicated that stronger interfacial interactions and better stability and dispersion of graphene in rubber matrices can be obtained by introducing functionalized graphene. Owing to the combination of hydrogen bonding and strong van der Waals interactions, the COOH-functionalized graphene behaves the best effect on the enhancement of mechanical and tribological properties of the nitrile rubber composites.

关键词： 同步性   稳定性   密实机理   非线性   混凝土颗粒流  

摘要： 对于激振器自同步理论,前期工作大多集中于单频驱动自同步振动系统的研究,缺乏外负载特性(如物料颗粒流效应)对单频及双频机械系统本身的影响分析。另外,在国家“一带一路”以及“十四五”规划政策驱动下,装配式建筑作为新型建筑工业化代表在全国各地得到大力推广。但到目前为止,混凝土预制构件作为装配式建筑主体材料,在生产中依然存在诸多缺陷,如密实不均匀,成型周期长等问题。究其原因,主要在于缺乏对预制构件制造设备系统动力学特性与密实机理的深入研究。为提高预制构件密实质量与效率,促进振动密实设备的大型化发展,本文考虑外负载颗粒流效应,将四机驱动振动系统与密实机理相结合,提出“四机驱动单频及双频机械系统的动力学特性及其振动密实机理”研究课题,在研究系统振动同步稳定性等基础上,展开对密实机理的深入研究。具体内容如下:(1)建立四机反向驱动单质体非线性机械系统动力学模型与数学模型,考虑混凝土颗粒流效应,研究系统实现单频及双频同步运转的理论条件、动力学特性及振动密实机理。考虑混凝土质量系数影响,基于平均法和Hamilton原理,渐近法和劳斯判据,分别得到系统实现单频及双频同步稳定的理论判据。依据微元法,研究并分析混凝土颗粒流的密实机理。针对前述理论结果,在数值上定性分析关键参数对系统动力学与运动学特性的影响,然后运用Runge-Kutta算法,对系统进行定量仿真验证。在上述理论与数值研究基础上,利用EDEM对混凝土密实效果进行离散元分析,以此揭示单频及双频条件下混凝土颗粒流在振动密实过程中的状态变化情况。最后,将单频与双频条件下的研究结果进行对比,总结出有利于混凝土密实的最佳系统参数匹配规则。(2)以配置限位装置的四机驱动双质体非线性机械系统动力学模型为研究对象,研究其同步理论、动力学特性与密实机理。首先应用渐近法,对非线性间隙橡胶弹簧刚度进行等价线性化处理。基于平均法与Hamilton原理,得到系统的同步性判据以及稳定性判据,然后利用微元法,揭示混凝土颗粒流的振动密实机理。在数值方面,对上述理论进行数值定性分析,并基于Runge-Kutta法和离散元法,进行振动定量仿真验证和离散元仿真分析。同时对混凝土颗粒流的运动状态进行矢量表达,提出混合均匀度的概念,对混凝土颗粒在振动过程中的运动状态以及混合程度进行详细分析,并界定出该振动系统的理想工作区域与条件。(3)考虑混凝土颗粒流的非线性效应,以四机分置驱动三质体动力学模型作为研究对象,对该系统进行有关同步稳定特性与密实机理的理论、数值定性分析与仿真研究。相较之前的研究,本部分采用激振器分置驱动方式。在理论上,推导出满足系统实现同步稳定运行的两个理论条件,并在满足系统实现竖直方向直线运动前提下,对混凝土颗粒流的密实机理进行理论分析。最后通过数值方法,对上述理论结果进行定性分析并做出仿真定量分析验证,最后得到实现较好密实效果所对应的系统最佳参数匹配区域。最后,对全文工作做出总结,同时指出未来仍需研究的问题。

关键词： 软体机械臂   动力学建模   约束环境  

摘要： 传统机器人刚性大、精度高,在工业、服务、医疗以及特种工作等诸多领域有着广泛的应用,但是高结构刚度也限制了机器人对环境的适应能力。软体机器人本体由柔性材料制成,容易实现连续形变,理论上具有无限被动自由度,能够根据周围环境改变自身的形状。与环境的接触能够提升软体机器人的适应能力,有效发挥软体机械臂的柔顺性特征,同时依靠环境接触也能获得更大的工作空间和端部稳定能力。但环境的接触增加了软体机器人的分布载荷,给软体机器人的建模和控制带来了巨大困难,因此对软体机械臂的动力学建模以及环境接触状态下的运动分析是非常重要的。针对实验室提出的水压驱动型软体机械臂,本文首先分析了柔性水压肌肉间耦合作用,推导了软体机械臂的内耦合静力学模型。其次,对传统变曲率模型进行改进,在环境约束点对离散单元进行二次分割,采用牛顿-欧拉递推方法建立了软体机械臂的动力学模型,解决了软体机械臂在约束环境下的姿态预测问题。最后,搭建了软体机械臂六自由度水压驱动试验系统,对所提出的数学模型进行了验证。本文的主要研究内容如下:(1)对单段软体单元进行内耦合影响分析,首先将单段软体单元的三个驱动单元分别独立进行分析,分别考虑不同驱动单元的受力,然后从单段软体单元内的驱动单元曲率恒定以及顶端固定件受力平衡的角度建立其内耦合作用模型。(2)建立约束环境下软体机械臂的运动学以及动力学模型。在分段常曲率模型的前提下,当软体机械臂与环境产生交互时,基于外部环境与机械臂的接触点,将其前后再分割为两段曲率连续但不同的圆弧。结合环境接触点的位置约束,得到软体臂的静力学姿态。基于牛顿——欧拉动力学,由内而外递推得到各离散段软体单元的运动参数,再由外而内递推得到各段离散软体臂的受力,最终求得动力学普遍方程。(3)搭建用于软体机械臂的试验系统,通过水压驱动系统控制软体臂按照预期目标进行驱动,同时利用Kinect传感器捕捉软体臂的姿态,与仿真结果进行对比,验证模型准确性。

关键词： 内燃机   直线发电机   结构设计   有限元仿真   电动力特性  

摘要： 永磁活塞机械-电力发动机是一种集成传统活塞式内燃机和直线发电机结构原理于一体的新型双元动力装置,保留了传统内燃机的曲轴连杆机构,加入了直线发电机的电磁结构,克服了传统内燃发电机组结构体积大、传递路线长、工作不协调、仅能输出单一能量等问题。本文通过仿真模拟与试验研究对永磁活塞-机械电力发动机的电动力结构与性能进行了研究,为结构优化设计提供理论依据。完成了整机动力学建模与结构匹配设计。依据传统内燃机和直线发电机的分析方法,建立了永磁活塞机械-电力发动机的系统动力学模型、电动力学模型和损耗模型,得到了动子组件的运动规律、受力平衡方程以及电机电磁解析式,提出了5个系统性能指标;基于168F汽油发动机的结构进行了改进设计,确定了动子组件和定子组件相关尺寸参数,完成了整个永磁活塞机械-电力发动机的几何建模。完成了电动力结构的三维有限元建模与分析。利用ANSYS Maxwell电磁仿真软件,建立了永磁活塞机械-电力发动机的三维有限元模型,以永磁体200℃的磁性能为基础对直线发电机部分进行了电动力仿真研究。对比分析了不同定子设计、不同充磁方向下的静磁场特性和额定工况(油门开度100%、转速3600r/min、负载电阻5Ω)环境下不同充磁方向的电动力特性,发现采用有铁芯的定子设计和轴向充磁的永磁体具有更好的电性能,依此进行了负载特性分析,得到了负载电流、负载电压和电磁推力的时域曲线,当负载电阻为5Ω时,负载电流有效值约为1A,电输出功率约为5W。对比168F汽油发动机的整体性能参数,发现虽然机械输出功率有所减少,但增加了电能输出,实现了双元动力输出。在不同工况环境下进行参数化仿真分析,得到了负载电阻和运动频率对负载电流、负载电压和电磁推力的影响规律,进一步计算得到了系统性能指标的规律曲线。随着负载电阻增加,电输出功率先增大后减小,而其它性能指标均增大;随着运动频率增加,电效率保持不变,机械效率先增大后减小,而其它性能指标均增大。当负载电阻为8Ω,运动频率为60Hz时,电输出功率最大为5.11W,此时电效率为65.84%,机械输出功率为3698.33W,机械效率为83.24%,热效率为33.88%,比原发动机仅减小了0.04%。依据数学模型,设计了一台永磁活塞机械-电力发动机的试验样机,利用电动机的机械能进行电动力匹配试验,得到了负载电压信号,与仿真数据较为接近,验证了有限元模型的准确性和结构原理的可行性。

关键词： 18650锂离子电池   机械滥用   热失控   失效模式   钻孔泡沫铝  

摘要： 新能源汽车因在运行过程中无尾气排放、绿色环保的优点不断被推广应用,但近年来出现了许多电动汽车因发生挤压碰撞造成安全事故,引发了人们对电动汽车安全的担忧。电动汽车的推广受到安全问题的制约。动力电池作为电动汽车的核心部件,对它的安全做全面研究至关重要。由于电动汽车碰撞事故的不确定性,碰撞的形式、碰撞的速度以及电池单体的荷电状态(State of Charge,SOC)都影响电池的安全性能。本文以18650圆柱形锂离子电池为研究对象,探究了不同加载工况、SOC、加载速度对电池安全性能的影响,研究了钻孔的闭孔泡沫铝结构对电池防护的效果。锂离子电池的失效过程复杂,包含了载荷、电压、温度三者的变化。在加载过程中,利用数字示波器和红外热像仪同步记录电池的电压和温度变化,分析电池在加载过程中的失效行为。主要有以下研究内容:(1)在径向平板压缩实验中,探究SOC和加载速率对电池单体安全性能的影响。在实验选取的准静态加载速度范围内,SOC为100%的电池在平板压缩过程中均出现剧烈的热失控现象,载荷最大值、温度骤升几乎同时发生。在实验选取的SOC范围内,以SOC为60%的电池为界限,SOC≤60%的电池失效时没有发生热失控而SOC>60%的电池发生了喷火爆炸剧烈热失控现象,高SOC电池热失控时温度有明显的传递过程。峰值载荷并不是简单随着SOC单调递增,峰值载荷的大小与电池是否发生热失控也有关系。由于平板压缩中高SOC电池热失控触发就在一瞬间,将名义模量的转折点作为电池失效的预测点。不同SOC电池的名义模量-位移曲线的变化趋势也相同,名义模量的峰值出现在载荷最大值之前。压缩后的电池经机械切割,发现电池在径向压缩下的剪切破坏和局部屈服失效。(2)在径向压痕实验中,探究了不同加载速度下电池的安全性能,比较了径向平板压缩和径向压痕两种工况下电池的安全性能。在所选准静态速度范围内,电池的载荷-位移曲线变化趋势一致,在压缩位移为4.3 mm附近,存在载荷-位移变化的转折点,后期变化速度较快,将该转折点作为电池失效的预测点。电池在径向压痕实验下载荷最大值、温度骤升几乎同时发生。分析电池在压痕实验下的失效过程,发现径向压痕下的电池因电池发生剪切破坏失效。与径向平板压缩相比,径向压痕实验是对电池局部加载,径向平板压缩是对单体电池整体进行加载,这两种工况下电池均出现起火爆炸等剧烈的热失控现象,但径向压痕下电池的最大载荷远低于径向平板压缩下的电池。(3)在电池轴向压缩实验中,研究了加载速度和SOC对电池安全性能的影响,分析轴向压缩载荷下电池的失效过程,讨论了电池在轴向加载和径向平板压缩下的异同。在实验选择的准静态加载速度范围内,电池的载荷-位移曲线类似;在实验采用的SOC取值范围内,电池在轴向压缩过程中电压均出现台阶式下降,直至完全短路。峰值载荷随着SOC的增大而略微增高。电池在轴向压缩下的失效均是侧面首先发生环形褶皱,然后发生破裂,破裂的位置均靠近正极。正极端的凹槽结构会诱导电池在轴向压缩下从靠近正极处开始破坏。与径向平板压缩相比,轴向压缩没有剧烈的热失控现象,轴向压缩电池的最大载荷也远低于径向平板压缩的,且轴向压缩电池电压具有特有的台阶式下降现象。电池轴向加载实验是沿极片的面内方向,加载过程中极片易出现褶皱式屈曲,而电池径向加载试验是沿着垂直于极片卷绕叠层的方向,加载过程中极片会出现压实。(4)在电池的防护试验中,进行了钻孔泡沫铝防护结构(利用泡沫铝做电池的防护材料,取形状为长方体的泡沫铝在其某截面钻圆形通孔,该通孔恰能放置电池)和内嵌电池单体的钻孔泡沫铝结构的平板压缩实验,从热量扩散和吸能变形两个方面讨论钻孔泡沫铝结构的防护效果,比较了有、无防护结构电池的失效。在内嵌电池的钻孔泡沫铝结构的径向准静态压缩实验中,SOC为80%的电池单体均发生热失控,泡沫铝防护结构能阻隔高温喷射物及火焰,很大程度上阻断了热量向邻近电池的传播。有、无防护结构电池均有层间断裂和局部屈曲弯折失效,有防护结构的电池层间断裂的层数较少,有防护结构的电池局部屈曲弯折多在外壳及其邻近极片,而无防护电池的局部屈曲弯折在电池内部。