表面黏附导致的接触行为转变

应用大规模分子动力学方法, 模拟了具有不同原子级粗糙形貌的两种刚性球形探头与弹性平面基体的黏附接触行为. 研究了载荷与真实接触面积、接触界面排斥力与真实接触面积, 以及黏附力与真实接触面积之间的关系. 分子模拟得到的载荷与真实接触面积的关系, 与连续力学接触理论预测很好地定性一致. 无论是原子级光滑探头还是粗糙探头, 黏附接触下的排斥力与真实接触面积的关系, 都与无黏附接触时的规律相一致, 即黏附力对接触行为的影响作用, 可以等效为附加在真实外载荷基础上的虚拟载荷, 将对黏附接触行为的分析转变为无黏附接触分析. 两种探头的黏附力随真实接触面积都呈幂函数形式的增长, 但是, 原子级光滑探头的幂指数大于1, 而原子级粗糙探头的幂指数小于1. 关键词： 接触行为 表面黏附 分子动力学模拟     

AgO_x界面插入层对GZO电极LED器件性能的影响

采用磁控溅射的方法在p-GaN上制备了GZO透明导电薄膜,通过在p-GaN和GZO界面之间插入AgOx薄层来改善LED器件的接触性能。研究结果表明:氮气退火后,采用界面插入层的AgOx/GZO薄膜电阻率为5.8×10-4Ω.cm,在可见光的透过率超过80%。AgOx界面插入层有效地降低了GZO与p-GaN之间的接触势垒,表现出良好的欧姆接触特性,同时使LED器件的光电性能获得了显著的提高。在50 mA的注入电流下,相比于常规的GZO电极LED器件,AgOx/GZO电极LED器件的正向电压由9.68 V降至6.92 V,而发光强度提高了13.5%。     

模切触超代数偶部到奇部的导子(英文)

本文研究了K模Wˉ1中K的非负偶次数的1上圈问题.利用计算导子在其生成元上作用,获得了简约定理和K模W1ˉ中K的非负偶次数的1上圈,推广了模切触超代数偶部导子.     

纸基食品接触材料中4-肉桂苯酚和水杨酸对叔丁基苯酯向干性食品模拟物TenaxTA的迁移

以纸基食品接触材料中的4-肉桂苯酚(CP)和水杨酸对叔丁基苯酯(TBS)为模拟迁移物,对其向干性食品模拟物Tenax TA中的迁移规律采用超高效液相色谱结合荧光检测(UPLC-FLR)方法进行了研究。在不同温度下对CP和TBS的迁移动力学进行了考察,并对其在封闭环境和敞开环境下的迁移率进行对比研究。通过设计不同质量的Tenax TA接触直径为3.5 cm圆片样品的迁移试验,探索了迁移试验中合适的模拟物质量/接触材料面积比条件。系列试验结果表明,迁移物迁移时间越长,迁移温度越高,相应的迁移率就越高;在高的迁移温度下,迁移物在Tenax TA上的解吸会导致迁移率的下降;在封闭条件下CP和TBS的迁移率要高于敞开条件下的迁移率;迁移试验中,4.16 g/dm²的模拟物质量/接触材料面积比是利用干性食品模拟物进行食品接触材料暴露评估的合适的迁移试验条件。密闭条件下市售的8种食品接触材料干性食品模拟物迁移实验研究表明,TBS存在于用于包装坚果类食品的包装纸中,含量为15.54 mg/kg。     

空气电晕辐照对聚酯薄膜表面组成及形貌的影响

分析了聚酯薄膜经空气电晕等离子体辐照处理后,其表面组成和形貌的变化。 结果表明,聚酯薄膜表面的活性基团在亲水环境中更倾向于迁移至表面,而不是向次表面或者基材本体内迁移。 薄膜表面C=O和O-H的引入量随电晕辐照强度的增加而增大,XPS结果表明,C-O、C=O和O-C=O的总含量增大,O1s谱图中新峰的结合能为532.49 eV,对应于聚酯薄膜表面过氧化物的-O-O-键。 原子力显微镜研究表明,聚酯薄膜经电晕辐照后,表面形成离散的球状颗粒,表面粗糙度变化范围在10 nm左右。     

盘-销摩擦系统摩擦接触力测试与特性分析

测量分析动态摩擦接触力是研究摩擦振动与噪声发生机理的关键.本文中建立了盘-销系统摩擦尖叫试验台架,成功再现了摩擦尖叫.采用三向力传感器对有无摩擦尖叫条件下的动态摩擦接触力进行了测量,并利用小波信号分解、概率密度函数、功率谱密度函数、时频分析等方法进行了分析和讨论.研究发现:在发生摩擦尖叫时,动态摩擦力和法向力发生高频波动,是系统噪声的激励源;无摩擦尖叫时的摩擦力和法向力的动态分量为典型的白噪声随机过程,呈非高斯分布;有摩擦尖叫时的摩擦力和法向力为窄带高频类谐波信号,摩擦力呈非高斯分布,而法向力近似为高斯分布;模态耦合是导致盘-销系统发生动态接触力高频波动以及摩擦尖叫的原因.     

Molecular dynamics studies on spreading of nanofluids promoted by nanoparticle adsorption on solid surface

Spreading of nanofluids on solid substrate was studied via molecular dynamics simulations. Simulation models for two immiscible fluids (oil and water based nanofluids) confined in a slit between two planar solid walls were set up. The influence of the volume concentration of the nanoparticles on the three-phase contact line motion was investigated. We found that the larger volume concentration results in more visible nanoparticle adsorption on solid surface. This effect further induces an advancing displacement of the contact line compared with the meniscus profiles in low concentration case and that with the absence of nanoparticles. These findings are consistent with the previous experimental and theoretical results and provide the atomic-scale understanding on nanofluid spreading.     

Stabilized interface methods for mechanical joints: Physics-based models and variationally consistent embedding

This paper presents the application of a new method for interfacial modeling utilizing a merger of continuous Galerkin and discontinuous Galerkin concepts to simulate the behavior of mechanical joints. The interfacial flux terms arising naturally from the discontinuous Galerkin treatment provide a mechanism to embed friction models in a variationally consistent fashion. Due to the unbiased implementation of the interface, facilitated by avoiding the master–slave concept, the deformation of the two interacting surfaces conforms to the local material and geometric attributes of the surfaces. This results in a better preservation of physics in interface mechanics. Additionally, the method is incorporated into a Variational Multiscale framework that comes equipped with a built-in error estimation module, providing numerical estimation of convergence and distinguishing discretization errors from modeling errors. A series of quasi-static numerical simulations of a lap joint under fretting conditions are conducted to compare the performance of two friction models: (i) classical Coulomb friction model and (ii) physics-based multiscale model. Hysteresis study of a three-dimensional double-bolted lap joint for the two friction models is also presented and the computed results are shown to be consistent between conforming and nonconforming meshes.     

Frictional moving contact over the surface between a rigid punch and piezomagnetic materials – Terfenol-D as example

A general theory of the frictional moving contact of piezomagnetic materials indented by a flat or cylindrical punch is set up. The rigid punch moves at a constant speed and the Coulomb friction law applies inside the contact region. Terfenol-D with high magnetostriction and coupling is chosen. Employing the Galilean transformation and Fourier transform, Cauchy integral equations of the second kind are obtained and solved exactly. Closed-form expressions of physical quantities on the surface in terms of elementary functions are given. Numerical analyses are conducted to reveal the effects of the friction coefficient and moving speed of the punch on various surface stresses and magnetic induction. The singularity, discontinuity and spike of the surface magnetic induction may be important factors to explain why surface damage occurs for piezomagnetic materials.     

大直径SHPB实验中的高温加载技术及其应用

为研究材料的高温动态力学行为,提出一套由自主设计的温控系统和100 mm SHPB装置组成的高温SHPB实验系统,采用ANSYS软件对界面热传导及其对实验结果的影响进行了计算分析,论证了该实验技术的可靠性,并对混凝土的高温动态力学性能进行了研究。结果表明:在大直径合金钢材质SHPB装置上对混凝土等热惰性材料进行高温冲击实验,冷接触时间临界值为1.00 s,本文中提出的高温加载技术可将冷接触时间控制在0.50 s以内,实验技术可靠;同一加载速率下,随着温度从常温升到1 000 ℃,高温混凝土的动态应力应变曲线呈现出塑性变化趋势,动态抗压强度先提高后降低,动态峰值应变则不断增大。