平面磨削金属结合剂金刚石节块的实验研究

本文研究了一种铁基结合剂金刚石节块的氧化铝砂轮平面磨削。通过在线测量水平和垂直方向磨削力，研究了氧化铝砂轮平面磨削加工金刚石节块过程中的法向力、切向力、力比以及磨削比能变化特征。观察了磨削后的金刚石节块表面特征。比较了逆磨和顺磨条件下的磨削特征。结果表明，顺磨条件下的法向力、切向力以及磨削比能均高于逆磨，但是切向力与法向力的比值在两种磨削方式下基本相同。     

金刚石砂轮平面磨削花岗石的实验研究

研究了花岗石的金刚石砂轮平面磨削.通过在线测量水平和垂直磨削力,研究了金刚石砂轮平面磨削加工两种天然石材过程中的法向力和切向力变化特征.建立了单颗磨粒承受平均切向和法向负荷与单颗磨粒最大切削厚度之间的对应关系.结合扫描电镜观察结果,探讨了两种花岗石的去除机理.     

锯切用节块中镀膜金刚石的效果评价

通过测量节块抗弯强度、节块在锯切过程中的耐磨性能以及锯切力比,研究了金刚石表面镀覆Ti-Cr合金对节块性能的影响.研究表明,相对于不镀覆的金刚石,镀覆金刚石使节块的抗弯强度和耐磨性能均有不同程度的提高.但是节块的抗弯强度与耐磨度并无单调对应关系.由于金刚石表面镀覆改善了结合剂对金刚石的把持和金刚石的出露状态,切削阻力降低,切向力与法向力的比值减小.     

微观天然橡胶摩擦性能研究

采用分子动力学方法模拟了刚性探头在天然橡胶基底表面滑动摩擦过程,利用模型体积随温度变化关系求得玻璃化转变温度(Tg)。重点讨论了探头与基底作用方式、温度以及滑动速度对摩擦过程的影响。结果表明,相比于强排斥作用,强黏着作用下基底对探头存在黏着力,在探头受到相等载荷时会获得更大的压入深度,加剧磨损,同时阻碍了探头切向运动,需要增大切向力平衡;温度低于Tg时,温度越低磨损程度越大,摩擦力变化趋势正相反;温度高于Tg时,摩擦力随温度升高而下降,磨损加剧;滑动速度增加,基底形变阻力增大,接触区域摩擦热无法及时释放,材料硬度降低,摩擦力小幅上升,表面磨损加剧。     

HDO共聚改性PET的流变性能及可纺性研究

为研究1,6-己二醇(HDO)对共聚酯流变性能以及熔融纺丝性能的影响规律，采用原位合成法制备了不同HDO含量的共聚改性聚对苯二甲酸乙二醇酯(PET)树脂。通过毛细管流变仪考察了共聚酯的流变性能，系统研究了HDO含量对共聚酯熔融纺丝性能的影响规律。结果表明，不同HDO含量的改性PET共聚酯属于典型的切力变稀型非牛顿流体，其流动方式为假塑性流动。共聚酯的黏流活化能随HDO含量的增加而下降，对温度敏感度下降，有利于纺丝；非牛顿指数n随温度的升高而增大，随HDO含量的增加而增大；共聚酯的结构黏度指数Δη随HDO含量增加而下降，说明熔体可纺性和稳定性较好。HDO改性PET共聚酯纤维与PET相比，各项性能指标未见明显差异，可纺性良好。     

连二亚硫酸钠遇水放热表观规律研究

连二亚硫酸钠具有遇湿易燃和遇热分解等性质，水解放热是其主要危险因素。本研究分别在绝氧和耗氧状态下实验确定了不同质量的连二亚硫酸钠在固定量水中的表观放热规律。结果表明连二亚硫酸钠遇湿耗氧放热量远远高于绝氧放热量，其遇水后耗氧总温升随水／连二亚硫酸钠质量比的增加呈对数减小。在固定空气流量下，单位质量连二亚硫酸钠的遇水放热功率随水／连二亚硫酸钠质量比的增加而线性升高。实验所得的连二亚硫酸钠表观遇水放热规律可为其火灾扑救提供参考依据。     

均匀橡胶弹性体隔声量的理论计算

由于材料在水声介质中的隔声性能的测试方法和测试设备较复杂，目前还没有在水声介质中的隔声量的标准测试方法。笔者从理论上研究了材料在水声介质中的隔声性能(隔声量)的计算方法，利用该方法计算了所合成的材料在不同厚度下的隔声量。计算结果表明：随着厚度的增加，材料的隔声量增加，但在低频下，当厚度增加到40mm以后，隔声量随厚度的增加而变化得很缓慢，在低频下不符合厚度每增加一倍，隔声量增加6dB这一规律。     

温度记忆型有机PTC导电材料发展概况

温度记忆型有机ＰＴＣ非线性导电材料，即材料特性如电阻率在一定温度范围内随温度循环具有良好重现性且随温度升高而增加并偏离欧姆规律的一种复合型导电高分子材料。对这一领域的国内外实验及理论、科研及开发应用研究现状做了综述；对该材料的一些典型性能与工艺问题进行了较全面的论述。     

敏化温度区奥氏体材料性能分析

分别对在不同超温温度、时间下,奥氏体材料的力学性能指标(冲击韧性、屈服强度、抗拉强度)和塑性指标(延伸率)的变化规律进行了分析.研究发现,随超温时间的增大,材料力学性能和塑性指标均下降,采用负对数曲线拟合了各温度下材料性能与超温时间的关系,得到了材料在对应超温条件下的寿命变化规律.     

聚氨酯复合泡沫塑料的动态压缩力学性能

针对几种不同密度、不同玻璃微珠填充比的聚氨酯复合泡沫塑料进行了动态压缩实验，研究了这类材料的宏观动态力学性能。结果表明，动态应力-应变曲线与准静态压缩加载下的应力-应变曲线具有相同的特征，也分为弹性区、平台区和致密区；在较大的应变率范围内，复合泡沫塑料的应变率效应是明显的，高密度复合泡沫塑料的屈服强度随应变率的增加而增加，而中、低密度材料的屈服强度则先随应变率的增加而提高，然后在某一高应变率下强度反而下降，材料表现出软化现象。     

Behaviors of time-dependent and time-independent adhesion forces revealed using an AFM under different humidities and measuremental protocols

Adhesion forces between a tipless cantilever and a silicon wafer were measured on an atomic force microscope (AFM) at two relative humidities (RH). Experimental results show that the behaviors of the adhesion force are largely influenced by the RH and measurement protocols. The capillary contribution to the measured adhesion force is time-dependent at low RH (31±1%) and time-independent at high RH (52±1%) due to different equilibrium times of water bridges. The time-dependent adhesion force increases logarithmically with contact time until saturation is reached. The effects of loading force, approach velocity, retraction velocity and measurement number on the adhesion force can be explained by the logarithmic contact time dependence of the adhesion force. However, the time-independent adhesion force decreases with dwell time, and increases with retraction velocity. No dependence of the adhesion force on loading force and approach velocity is found. The adhesion force by consecutively measurements on the same location shows fluctuations, and the trend is unpredictable.     

Influence of a Tangential Force on the Fracture of Two Contacting Elastic Bodies

The problem of fracture initiation at two elastically contacting structural components, subject to applied normal and tangential forces, was analyzed. The fracture initiation load was predicted to depend sensitively on the magnitude of the applied tangential force and the interfacial friction coefficient, and to exhibit important dependencies on the fracture toughness, elastic modulus, and curvature of the contacting bodies. Experimental results obtained on glass and Si₃N₄ conform with the trends predicted by the analysis.     

ROTATIONAL DISSIPATION DURING MICROSPHERE IMPACT

In this study the dissipative effects due to microsphere rotation in the presence of adhesion during contact were investigated by means of mathematical analysis and numerical simulation. Three sources of rotational moments were considered: a moment about the mass center of the tangential contact force, a moment associated with the material rolling deformation and another with the peeling of the adhesion bond. The latter two are couples proximate to the contact region. A numerical model based on the results of the mathematical analysis was used to simulate the two-dimensional normal and oblique impact of a microsphere. The results show that the magnitude of rolling deformation and adhesion bond peeling moments are proportional to a power of the contact radius. Consequently, because of the small radius of microspheres, the effect of rotational dissipation due to these moments can be neglected. For example, when predicting microsphere rebound during impact, only the moment of the tangential force needs to be considered when considering microsphere rotation.     

Geckos’ foot hair structure and their ability to hang from rough surfaces and move quickly

Geckos generate the necessary adhesion force through their foot hair. The direction of the gecko's foot hair is not perpendicular to its finger surface, giving compliance to the hair. The effect of this compliance on the adhesion force is analysed and expressed theoretically in terms of contact mechanics. We conclude that the compliance of the foot hair is sufficient to generate the large adhesion force necessary for adhesion to rough surfaces, and that the structure of the seta with the spatulae allow the normal adhesion force to be controlled, allowing the gecko to make quick steps.     

Nano-scale friction of polystyrene in air and in vacuum

Using atomic force microscopy (AFM), we measured friction between an AFM tip and a polystyrene surface at 25 °C, as a function of the sliding velocity and the applied normal load, both in air and under vacuum conditions. The objective was to analyze the influence of humidity on the frictional behavior of polystyrene. Our experimental results as a function of sliding velocity revealed a logarithmic increase of the friction force in air whereas a logarithmic decrease of this force is found in vacuum. Our comparative results unveil that two different dissipation mechanisms are dominating the frictional behavior of polystyrene in air and in vacuum. We propose a tentative explanation.     

Temperature dependence of microscale adhesion force between solid surfaces using an AFM

The adhesion force between two solid surfaces is of great interest with the rapid development of micro–nanodevices and instruments. The effect of temperature on the microscale adhesion force has been studied by recording force–displacement curves with an atomic force microscope. A flat tip with a diameter ~1.73 μm was used to prevent wear. The adhesion force measurements were carried out under ambient conditions and in a nitrogen-filled glove box. The substrate temperature was varied between 30 and 200 °C. The results show that when the temperature is <200 °C, the influence of temperature on the normal spring constant of the cantilever can be ignored. In this temperature range, the adhesion force distribution for each temperature exhibits a Gaussian-like distribution under both situations. Under ambient conditions, the mean adhesion force first increases with the increase in temperature and reaches the maximum at ~100 °C. Then the adhesion force begins to decline slightly. At about 150 °C, the adhesion force decreases dramatically, and remains relatively stable at high temperatures. The increase in adhesion force is associated with the capillary force. The elevated temperature leads to larger and more numerous liquid bridges. The capillary nucleation, the diffusion of water molecules, and the flow of thin water film are all enhanced with the elevated temperature. However, in dry nitrogen, the mean adhesion force decreases with the increase in temperature. This trend is attributed to the broken van der Waals bonds.     

陶瓷轴承外圈内圆磨削力与表面质量研究

为了探究陶瓷轴承外圈内圆(简称外圆)磨削力以及磨削力对表面质量的影响机制,通过磨削实验首先获得了不同磨削参数对外圆磨削力的影响规律,其次得出了旋转磨削力与表面粗糙度和表面去除方式的关系。结果表明,随着砂轮速度减小,进给量和工件转速增加,陶瓷外圆磨削法向与切向磨削力均增加,且法向磨削力是切向磨削力的3倍左右;当磨削力增大,磨削表面由塑性去除向脆性去除转变,表面粗糙度值增大,表面质量变差。在陶瓷轴承外圆磨削时可适当选用较高的砂轮速度、较小的进给量和工件转速以保证表面加工质量和加工效率。     

Evolution and level behavior of adhesion force by repeated contacts of an AFM colloid probe in dry environment

Adhesion forces between a colloid probe and some samples were consecutively measured at a single location with an atomic force microscope (AFM) in a dry environment. The outcomes show that the adhesion force depends considerably on material, contact history, and number and distribution of asperities within the contact zone. Generally, there are four different stages for the adhesion force with increasing measurement number: random behavior for the first several or tens of contacts, then increasing monotonically, later remaining stable, and finally decreasing. Usually, the measured data points are grouped into several levels. Moreover, the adhesion force jumps frequently between different levels and is more inclined to jump to a neighboring level. The level behavior was attributed to the fact that the real contact region is not exactly the same between successive measurements. The differences in the adhesion force between two neighboring levels are almost the same for one location. The adhesion force in some levels usually increases or decreases discontinuously after jumping to other levels and then jumping back. The magnitude and fluctuations of the adhesion force and the number of levels depend on the number and distribution of asperities in the contact zone.     

Interactions Between Micron-sized Glass Particles and Poly(dimethyl siloxane) in the Absence and Presence of Applied Load

A technique using a scanning electron microscope to view a fine particle in contact with a flat substrate whilst under load and during its removal is described. The particle is attached to an atomic force microscope cantilever so that the magnitude of the load can be estimated directly from the imaged deflection. Interactions between 5 to 60 μm spherical glass particles and cross-linked poly(dimethyl siloxane) were studied in the presence and absence of load. W_A was estimated to be 74 mJ/m² from the size of the contact area in the absence of load. Using highly flexible cantilevers to apply load resulted in large shear displacements and forces, which distorted the contact area and assisted in particle removal. These shear effects were eliminated by using a more rigid cantilever to measure a normal pull-off force for which the interface toughness, G_c , exceeded 950 mJ/m². The large adhesion hysteresis indicated the presence of chemical bonding, presumed to occur between silanol and siloxane groups. The mode of particle detachment varied significantly with the choice of cantilever, showing evidence of both cohesive failure and interfacial crack propagation. The relevance of these results to the interpretation of AFM data is discussed.