微凹坑织构表面对脂润滑关节轴承摩擦特性的影响

为研究脂润滑下表面织构对关节轴承摩擦特性的影响,设计和制造了4组表面高度算术平均值相同、表面微凹坑面积占有率分别为7%、10%、15%和21%的关节轴承内圈表面形貌.使用Talysurf CCI Lite非接触式三维轮廓仪对试件表面进行测量,采用ISO25178定义的表面参数对试件表面形貌进行表征.在改造的HDM-20端面摩擦磨损试验机上,采用2#锂基脂润滑在不同载荷、转速条件下进行了一系列摩擦磨损试验,研究了表面形貌参数与摩擦系数的关系.在本试验中,选取表面高度算术平均值Sa和表面峰态Sku等表面高度参数、表面峰区平均材料体积Vmp、表面中心区平均空体体积Vvc和表面谷区平均空体体积Vvv等表面功能参数以及平均谷体积Sdv等表面特征参数对关节轴承表面形貌进行表征.结果表明:各表面参数对摩擦系数的影响不同,将表面高度参数、功能参数和特征参数这几种表面形貌参数结合对关节轴承表面形貌进行表征,更有利于脂润滑下关节轴承表面形貌的摩擦学设计.     

微纳米摩擦的弹性棘轮模型与形貌的尺度效应

建立了弹性棘轮模型并用于研究微观形貌参数对摩擦性能的影响,通过研磨和抛光的方法在硅材料表面进行形貌修饰,并采用原子力显微镜和自制微摩擦测试仪分别在纳米和微米尺度下进行摩擦力测量试验.结果表明：硅表面经过形貌修饰后,摩擦力不仅与粗糙峰的斜率有关,而且与接触副的等效曲率半径相关;在纳米尺度下,粗糙峰斜率对摩擦力的影响较大;在微米尺度下,等效曲率半径对摩擦力的影响较大;棘轮模型只适用于斜率影响为主导因素的情况,而弹性棘轮模型由于综合考虑了形貌斜率和等效曲率半径的影响,能够更好地描述不同尺度接触副的摩擦规律.     

CMP加工后芯片三维形貌表征参数体系

针对当前化学机械抛光(chemical mechanical polishing, CMP)后的芯片表面形貌的表征常常只停留在研究二维轮廓特征，无法完整地表达整个三维表面形貌信息，仅使用单一的评定指标来表征其表面的不平整程度等问题，建立了1个科学、全面的芯片表面形貌评定参数体系应用于工程表面粗糙度评定中，通过分析芯片表面形貌的幅值分布特征，结合芯片表面的统计特性，基于ISO 25178-2标准表征参数建立适用于芯片表面三维评定的表征参数体系. 仿真结果表明:CMP加工后芯片表面形貌的幅值近似服从高斯分布；分形维数D可以准确表征芯片表面形貌，反映其复杂程度；通过幅度参数、空间参数、混合参数和分形参数建立的芯片表面形貌评定体系能够从多方面表征芯片三维表面形貌特征，对芯片表面形貌参数评定具有一定的可行性.      

蠕墨铸铁／40Cr配副干摩擦三维表面形貌特征研究

采用探针式三维表面形貌仪考察了销－盘式干磨擦试验条件下蠕墨铸铁度销磨损表面的三维形貌特征。结果表明：度销磨损表面主要呈现犁沟型、孤岛型及二者的混合型３种形貌特征,其中具有孤岛型磨损表面形貌特征的试样的摩擦系数较高,磨损率较低;而具有犁沟型磨损表面形貌特征的试样的摩擦系数最低,磨损率最高,分析表面形貌参数发现：犁沟型表面形貌具有最大的表面高度偏差和表面空隙率及高负值的表面高度分布参数;而孤岛型表面形貌的表面高度偏差和表面空隙率最小,表面高度分布参数为高正值。     

蠕墨铸铁干摩擦表面形貌研究

运用三维表面形貌测试技术,分析了蠕墨铸铁的干摩擦表面接触形貌特征,并从传热学的角度分析了摩擦表面形貌特征与其干摩擦学特性的关系,结果表明：蠕墨铸铁干摩擦表面主要有犁沟型、弧岛型和犁沟－弧岛混合型３种特征形貌,犁沟型和弧岛型特征形貌沿垂直于摩擦表面方向不对称分布;而混合型特征形貌沿垂直于摩擦表面方向对称分布;犁沟型表面形貌的最大高度最大,空隙率最高,而弧岛型表面形貌的最大高度最小,空隙率最低;表面形     

粗糙薄层弹性体接触刚度分析

薄层弹性体功能结构表面在工程领域有着广泛的应用前景,薄层弹性体的接触特性分析对功能结构表面设计与应用非常重要.采用随机粗糙表面模拟生成技术和有限元分析技术建立了粗糙薄层弹性体表面的接触刚度确定性分析模型,研究了薄层弹性体的接触特性,对基于半数值确定性分析方法的粗糙层-基体层串联模型用于粗糙薄层弹性体接触刚度计算的适用性进行了讨论,进一步分析了粗糙薄层弹性体串联模型接触刚度的误差来源.研究结果表明:当薄层弹性体的基体层厚度小于10倍表面均方根粗糙度时,由传统粗糙层-基体层串联模型分析获得的粗糙薄层弹性体刚度误差将超过15%,误差主要来源于粗糙峰的大变形和基体层的局部变形不均匀的共同作用.     

砂轮约束磨粒喷射加工表面的分形及摩擦特性研究

对砂轮约束磨粒喷射精密光整加工(Abrasive Jet Precision Finishing,AJF)表面进行分形维数和摩擦磨损特性研究.试验在MB1332A外圆磨床上完成,加工式样为Ra为0.6μm左右的45#钢.加工表面形貌和微观几何参数用MICROMESVRE2表面轮廓仪测量;应用分形维数和功率谱密度函数评价磨削加工和光整加工表面的微观形貌特征;利用MG-2000型销盘式高速高温摩擦磨损试验机研究表面形貌和分形维数对摩擦系数和磨损性能的影响.试验结果表明:磨粒喷射精密光整加工使工件表面高度特性参数大幅度降低,轮廓波动平均间距减小,波纹细密性提高.随着加工循环的增加,Ra值由0.6μm下降到0.2μm左右.光整加工表面摩擦系数和磨损量与磨削加工表面相比明显降低,摩擦磨损试验结果和分形维数变化相吻合.     

粗糙磨损表面特征的双谱分析

采用双谱分析技术，结合表面粗糙度偏斜度评定参数的定义，给出了偏斜度函数的双谱表达式；在对工程粗糙表面的偏斜度进行理论研究的基础上，分析了精密车削和磨削加工试件磨损前后表面高度分布的偏斜度．结果表明，可以用双谱和偏斜度函数对粗糙磨损表面非对称高度分布进行直观和便捷的评价．     

基于多轴疲劳准则的齿轮点蚀寿命预测

综合齿轮动力学和弹性流体动力润滑理论，建立基于临界平面法多轴疲劳寿命预测模型.首先根据齿轮啮合特性获取齿面接触的时变参数，采用平均滤波方法模拟齿面磨合后的粗糙状态，并将齿面粗糙形貌带入油膜厚度计算，并基于量纲化差分方法建立齿轮的热弹流动力润滑模型；随后，通过润滑界面压力和摩擦力的分布计算近表面应力状态，确定接触近表面任意平面的应力与应变幅；最终，采用临界平面方法计算Smith-Watson-Topper(SWT)参数和最易萌生裂纹的平面，最终确定齿轮疲劳点蚀寿命，并试验验证模型有效性.结果表明：粗糙表面造成压力、油膜厚度和温度等波动较大，最大应力集中分布在表面，疲劳点蚀的微裂纹首先在表面萌生；齿轮疲劳点蚀数值模型可有效预测不同润滑条件下的疲劳点蚀寿命.     

机械密封织构化表面粗糙度效应的有限元模型与摩擦学特性分析

为研究粗糙度效应对机械密封织构化端面承载能力、摩擦学特性以及密封性能的影响，基于有限元法建立了机械密封的混合润滑模型，针对确定性非高斯随机分布粗糙表面，考虑润滑液膜的宏微观空化作用和粗糙峰的接触，研究了圆孔型织构化机械密封的摩擦学性能和密封性能. 结果表明:平衡状态下处于全膜润滑区间的非高斯型粗糙织构表面，在研究范围内均方根值越大的表面其减摩效果越好，且泄漏率越大，从混合润滑区到全膜润滑区转变的速度也随之增大；非高斯表面的偏态值和峰态值对密封表面的承载能力，润滑性能以及密封性能有影响，但无明显规律；在混合润滑区，圆孔织构具有增摩效果，而在全膜润滑区表现出减摩效果.      

5级人防口部粘钢封堵接头抗爆实验研究

通过粘钢实现一典型汽车库人防口部封堵的设计方案,并对原设计方案进行相似设计后,对粘钢接头结构实验模型在核爆炸压力模拟器中进行模爆实验,得到沿竖向支座钢板的位移和应变时程曲线,并和有限元数值解进行了对比,其结果均较吻合,通过沿竖向支座钢板的应变分布规律得到钢板-混凝土界面之间的粘结应力;检验了在5级人防爆炸冲击波作用下,混凝土墙与钢板间粘结面承载力的可靠性;分析了5级人防爆炸荷载作用下支座钢板沿竖向应力的分布规律,为确定混凝土墙与钢板之间粘结应力的计算方法提供了参考。     

Microstructure-based crystal plasticity modeling of cyclic deformation of Ti–6Al–4V

Ti–6Al–4V is a dual phase material with range of possible complex microstructures. It is well known that mechanical behavior of Ti–6Al–4V is significantly affected by its texture and microstructure morphology. A three-dimensional microstructure-based constitutive model for monotonic and cyclic deformation of duplex Ti–6Al–4V is developed and implemented. The model includes length scale effects associated with dislocation interactions with different microstructure features, and is calibrated using polycrystalline finite element simulations to fit the measured macroscopic responses (overall stress–strain behavior) of a duplex heat treated Ti–6Al–4V alloy subjected to a complex cyclic loading history. Representative microstructures are simulated using a three-dimensional finite element mesh with periodic boundary conditions imposed in all directions. The measured orientation and misorientation distributions of grains of this duplex Ti–6Al–4V are considered, and similar probability density distributions of the crystallographic orientations are assigned to the finite element mesh. The misorientation distributions are then fit using the simulated annealing method. Effects of microstructural features are examined and compared with the experimental data in terms of their influence on the material yield strength. The results are shown to be in good agreement with the experimental observations.     

超高强度平头圆柱形弹体对低碳合金钢板的高速撞击实验

为分析不同组分低碳合金钢板抗超高强度低碳合金钢弹体的高速撞击性能及破坏模式,以两种典型防弹特种钢SS、AS以及常见的Q235A钢为研究对象,通过静态拉伸、静态压缩及动态压缩测试,获得静态拉伸和压缩性能参数以及1 000~6 000 s-1应变率范围内的力学行为,分析了材料组分与力学性能的相关性。采用弹道枪加载撞击方法,获得了两种超高强度合金钢平头圆柱形弹体对3种钢板(14.5~15.9 mm厚)的弹道极限速度,通过分析获得了不同工况下的极限比吸收能,讨论了合金钢板在弹体高速撞击下破坏模式的差异,分析了材料力学性能与破坏模式的相关性。研究表明:3种合金钢板抗弹体撞击性能与材料屈服强度正相关,但其性能间的差异远小于屈服强度间的差异;在超高强度合金钢平头圆柱形弹体的高速撞击下,3种钢板的失效机制与其力学性能密切相关,Si和Mn含量高的AS钢呈硬脆性特征,其断裂失效主要取决于材料的剪切强度,而Si和Mn含量较低的SS钢和Q235A钢具有良好的塑性,其断裂失效主要取决于材料的压缩强度和剪切强度。     

基于逆复合二次径向基函数的对称复合材料层合板自由振动分析

利用逆复合二次径向基函数无网格配点法对Reddy的高阶剪切变形理论进行离散,预测了对称复合材料层合板的自由振动特性.将不同材料参数、几何尺寸和边界条件的层合板固有频率计算结果与相关文献中的结果进行对比,结果表明:逆复合二次径向基函数在对称复合材料层合板自由振动分析方面具有收敛性好及精度高等一系列优点.     

巨型型钢混凝土柱双向偏心受压校核分析方法

利用ETABS截面设计器对某超高层建筑巨型型钢混凝土柱截面进行了双向偏心受压校核分析.首先由ETABS截面设计器得到构件截面相关曲线数据,通过编制的拟合及绘图程序采用空间相关曲面法对构件进行校核分析,针对空间相关曲面法的不足进一步提出了等效平面相关曲线法加以改进.等效平面相关曲线法基于映射原理将空间相关曲面转换成等效平面相关曲线,同时将空间内力点转换成等效内力点,方法直观简便,可在一个图形中给出各工况的校核结果,并且能定量地给出构件受力的安全程度.最后,以一个巨型型钢混凝土柱截面为例给出了等效平面相关曲线法的校核结果,对比了考虑型钢作用及不考虑型钢作用两种情况对巨型柱受力性能的影响.文中提出的方法可为类似工程和建筑结构设计软件的开发提供借鉴.     

Prevention of thermal bending of multilayered beams and plates

A method is described to prevent bending in multilayered beams and plates of different isotropic materials with uniform and nonuniform temperature distribution through the thickness. The method involved the addition of an extra layer to the multilayered beams or plates. With the proper selection of the thermoelastic properties, the added layer would eliminate the curvature produced prior to this addition. A complete analysis for the determination of the various thermoelastic parameters of the extra layer was made. In addition, to ensure that the multilayered beams and plates actually remained straight, a thermoelastic analysis was performed for the solution of thermal stresses and strains in the laminate. The results gave assurance to the straightness of the laminate since the calculated strains have the same value throughout the thickness. The solutions are valid for any given uniform temperature change and for any given nonlinear temperature distribution through the thickness of the multilayered beams and plates. Several numerical examples are presented that illustrate the application of the method for various temperature distributions. A simple experiment was conducted that showed the validity of the analytical method. A brass strip was added to a bimetalic strip made of aluminum and steel at room temperature. The thickness of the brass strip was calculated from the theory to prevent bending. The trimetal strip was placed in a furnace and, as expected, it remained straight for varying temperatures.     

An examination of the competition between bulk behavior and interfacial behavior of ceramics subjected to dynamic pressure-shear loading

A grain level micromechanical analysis of ceramic microstructures subjected to dynamic compression-shear loading conditions is presented. The investigation consists of a combined experimental/numerical approach in which bulk and surface properties are examined by means of pressure-shear impact experiments for a ceramic plate in contact with steel plates. The model for the ceramic microstructure accounts for heterogeneities and randomness in grain orientation and composition. A cohesive zone model is included to capture inter-granular microcrack initiation and evolution as a natural outcome of the calculated material response. Surface roughness is also included in the analysis to capture the time-dependent frictional behavior of the various interfaces. The model for the steel anvil plate accounts for visco-plasticity, thermal softening and strain hardening. Representative volume elements of ceramic microstructure and anvil plates are considered to account for features observed in real experiments. Pressure-shear impact velocity histories are used not only to identify inelasticity, but also to determine dominant failure modes. Bridging between micro- and macroscales is achieved by using the developed model. Simulated velocity histories have been found to be in a good agreement with the experimental observations when bulk and surface features are included in the analysis. However, it is demonstrated that information gathered from these experiments is not sufficient to determine the mechanical behavior of the brittle material. Instead, the velocity histories provide important information on the time-dependent frictional behavior of the specimen-anvil interfaces.     

带槽平板的三维应力集中效应

本文提供了用电阻应变片方法测量一组不同厚度的带有对称圆槽的拉伸平板在应力集中部位的应力分布情况。实验结果表明,应力集中系数不仅与板平面的几何尺寸有关,而且与板的厚度有关。     

Compressive strength of fibre composites with random fibre waviness

The compressive strength of unidirectional long fibre composites is predicted for plastic microbuckling from a random two-dimensional distribution of fibre waviness. The effect of the physical size of waviness is addressed by using couple stress theory, with the fibre bending resistance scaling with the fibre diameter d. The predicted statistical distribution of compressive strength is found using a Monte Carlo method. An ensemble of fibre waviness profiles is generated from an assumed spectral density of waviness and the compressive strength for each such realisation is calculated directly by the finite element method. The average predicted strength agrees reasonably with practical values, confirming the hypothesis that microbuckles can be initiated by fibre misalignment. It is found that the probability distribution of strength is well matched by a Weibull fit, and the dependence of the Weibull parameters upon the spectral density of waviness is determined. For the practical range of fibre distributions considered, it is concluded that the strength depends mainly upon the root mean square amplitude of fibre misalignment, with the shape of the power spectral density function playing only a minor role. An engineering model for predicting the compressive strength is proposed, akin to weakest link theory for materials containing flaws. A specimen containing randomly distributed waviness is examined to locate regions of high-fibre misalignment. The strength of each of these weak regions is estimated from a look-up table derived from calculations with idealised circular or elliptical patches of waviness. The strength of the composite is given by the failure stress associated with the weakest such patch. For random distributions of waviness, the predictions using this engineering approach are in good agreement with the direct calculations of strength using the finite element method.     

Buckling load of seismic isolators affected by flexibility of reinforcement

Using the thinner steel reinforcing plates in the elastomeric multilayer isolators could reduce the weight of the isolators but would have a large effect on the buckling load of an isolator, which cannot be analyzed by the Haringx theory, a traditional approach on the stability analysis of rubber bearings. The buckling load of the isolators, which includes the effect of the flexibility of the steel reinforcing plates, is analyzed by a beam theory in which shear deformation and warping of the cross-section are considered. Pressure distributions in the elastomeric layer bonded to flexible reinforcements under compression force, bending moment and warping moment are derived from an assumed displacement field, from which the warping-related parameters used in the beam theory are established. The thickness of the steel reinforcement in the isolators is determined from the buckling load of the isolators, which is solved from a cubic equation established by the beam theory.