磨粒图象纹理分形特征的研究

机械设备在运转过程中,发生各种各样形式的摩擦磨损,其磨损颗粒的数量、尺寸大小都随着运转过程而逐渐增加,在颗粒表面留下了与摩擦磨损机理相关的痕迹。这对磨粒的表面纹理特征进行分析,通过求取特征值,作为判断出机械装置的寿命、故障机理等指标的重要参数。     

TC4钛合金磨削机理和仿真研究

Ti-6Al-4V(TC4)钛合金属于航空航天构件中广泛应用的难加工的材料,其磨削加工表面质量具有较高的要求,磨具与钛合金表面的接触过程十分复杂.为探索其微观磨粒磨削中的切削力、切削温度、切屑形态等变化,开展TC4钛合金三维单颗磨粒磨削加工机理及仿真技术研究.基于磨削基础理论及钛合金材料性能,分析建立单颗磨粒磨削加工物...     

基于图像分形计算的磨粒定量参数识别研究

磨粒分形研究是磨粒分析技术中的热点.为了得到有效的磨粒分形定量特征,介绍了分形原理和磨粒的分形特性,在计算机和图像处理技术基础上,研究了磨粒分形参数提取.通过探寻磨粒边缘轮廓及纹理分形两种分形维数的计算方法,对大量典型磨粒分形维数进行了定量计算和统计分析,得出了相应的分布范围.给出了计算的一般方法和实例,提供磨粒分析的新的定量特征参数,是磨粒识别的一种有效途径,为最终解释磨损的机理提供了前提.     

基于分形特征的磨粒图像分割

磨粒图像分割是磨粒图像分析的关键一步,分割结果的准确性将直接影响磨粒的最终识别和分类。分形理论在表征磨粒的轮廓特征和表面特征方面得到了广泛应用。结合磨粒图像的分形特征和自组织特征映射神经网络,提出基于分形特征的磨粒图像分割方法。首先,计算磨粒图像的分形维数,多重分形维数,结合图像的灰度信息,共得到图像的8个特征;然后,利用自组织特征映射神经网络的自组织、自学习特性,实现磨粒图像的分割。磨粒图像分割的结果表明,该算法是可行的、有效的。     

基于磨损机理的磨粒图像识别仿真

机械设备磨损过程中产生的磨粒,可以利用智能识别技术进行识别。通过对切削磨粒、球状磨粒、疲劳磨粒以及严重滑动磨粒的磨损机理的研究,提出了能够识别各类磨粒的显著特征,将特征参数进行量化表征,并以特征参数为输入向量,建立支持向量机分类器模型,运用层次法对分类器进行训练,优化分类器的参数,最后利用分类器模型对磨粒图像进行识别以验证识别方法的可行性。实验结果表明,支持向量机分类器识别磨粒类型准确率较高,可以用于磨粒图像的识别。     

基于LabVIEW的机械密封端面真实接触面积数值模拟

机械密封端面的真实接触面积对端面间的摩擦磨损特性和密封性能有着重要的影响;依据分形理论,考虑摩擦作用的影响,建立了机械密封端面无量纲真实接触面积的计算模型;基于LabVIEW编制了机械密封端面真实接触面积数值模拟程序,通过数值模拟计算得到了NHM70型机械密封端面间的无量纲真实接触面积Ar与端面比载荷Pg、端面分形维数D及特征尺度系数G的关系曲线;研究表明,真实接触面积随着端面比载荷的增大而单调地非线性增大;随着特征尺度系数的增大先急剧减小,而后缓慢减小;随着分形维数的增大先增大,后减小,即存在一最佳分形维数,使密封端面间的真实接触面积最大.     

滚动接触疲劳载荷对铁轨表面接触疲劳裂纹应力强度系数的影响

为研究轮轨滚动接触疲劳(Rolling Contact Fatigue,RCF)载荷对铁轨表面裂纹应力强度系数的影响,以UIC60铁轨轮廓尺寸为依据建立轮轨接触的三维有限元模型,通过改变RCF载荷大小、轮轨表面摩擦因数和接触中心位置等轮轨接触的输入参数,计算铁轨表面接触裂纹尖端的应力强度系数,分析RCF载荷对铁轨表面接触疲劳裂纹的影响.结果表明RCF载荷作为控制铁轨表面接触裂纹的重要因素,其变化直接导致裂纹尖端应力强度系数的变化,从而改变裂纹的扩展状况.为减缓铁轨表面裂纹的扩展,可以针对载荷采取均匀分布载重量、使用润滑剂降低轮轨摩擦因数等相应措施.     

滚动接触疲劳载荷对铁轨表面接触疲劳裂纹应力强度因子的影响

为研究轮轨滚动接触疲劳（Rolling Contact Fatigue,RCF）载荷对铁轨表面裂纹应力强度因子的影响,以UIC60铁轨轮廓尺寸为依据建立轮轨接触的三维有限元模型,通过改变RCF载荷大小、轮轨表面摩擦因数和接触中心位置等轮轨接触的输入参数,计算铁轨表面接触裂纹尖端的应力强度因子,分析RCF载荷对铁轨表面接触疲劳裂纹的影响. 结果表明RCF载荷作为控制铁轨表面接触裂纹的重要因素,其变化直接导致裂纹尖端应力强度因子的变化,从而改变裂纹的扩展状况;为减缓铁轨表面裂纹的扩展,可以针对载荷采取均匀分布载重量、使用润滑剂降低轮轨摩擦因数等相应措施.     

基于图像处理的输电线路导线表面损伤特征研究

导线表面损伤是影响架空输电导线力学性能和电气性能的重要因素,研究导线表 面损伤特征对输电导线耐久性设计和安全性评估具有重要意义。为此选取不同地区实际输电线 路中截取的不同电压等级的典型导线 (钢芯铝绞线) 作为研究对象,利用图像处理技术提取了 不同导线损伤表面图像信息。针对传统像素点覆盖法的不足提出一种改进的像素点覆盖算法, 给出了导线表面损伤特征与分形维数间的关系。研究结果表明,导线表面形貌具有明显的分形 规律,分形维数能够度量架空输电导线表面的损伤特征。导线表面损伤程度越低,二维分形维 数越小;导线表面不平整度的增加将使得三维分形维数增加。导线表面损伤特征为伤痕时,二 维分形维数介于1.5~1.7 之间;损伤特征为磨损时,二维分形维数介于1.2~1.4 之间;损伤特征 为锈蚀时,二维分形维数介于1.4~1.5。     

基于粒子群优化算法的金刚石砂轮磨粒边缘提取

为了实现对金刚石砂轮磨粒边缘的有效提取,将基于粒子群优化算法的Canny 算 子应用在金刚石砂轮磨粒的边缘检测上。用最大类间方差作为目标函数,优化Canny 算子的阈 值,实现边缘的有效提取。分别对实测的单颗磨粒和多颗磨粒进行了边缘提取,实验结果显示 该算法可以较好地提取金刚石砂轮磨粒边缘。该方法不需要人为设定阈值,可以实现阈值的自 动获取和优化。最后,利用四连通成分和八连通成分与像素总数的比值,将阈值可优化设定的 Canny 算子与传统的Canny 算子以及最大类间方差的方法做对比,结果表明所应用的方法有效 地提高了检测的准确性。     

Continuum damage mechanics analysis of strip tearing in a tandem cold rolling process

Strip tearing during tandem cold rolling is one of the manufacturing issues in the rolling industry that can significantly increase production costs. In this paper, an explicit finite element code coupled with the improved Lemaitre damage model is developed to predict strip tearing in a five-stand tandem rolling mill. The simulation results are validated using experimental data from an industrial rolling mill, and there is good agreement between the numerical and experimental results. Some factors related to strip tearing, such as friction coefficient variations, thickness difference between two welded strips and reduction schedule, are introduced, and their influence on the damage evolution through the strip during the process is investigated by using damage-coupled finite element simulations.     

Simulation of media behaviour in vibration assisted abrasive flow machining

Abrasive flow machining (AFM) is an abrasive-based precision finishing process used for achieving surface finish in micro and nano-level. The AFM polishes surfaces by extruding a visco-elastic media in contact with the workpiece. The media, also called a ‘flexible tool’, plays a key role in the performance of the process. Ultrasonic assisted abrasive flow machining (UAAFM) is a new variant of the AFM process in which the workpiece is subjected to mechanical vibration orthogonal to the media flow direction. In this process a high frequency, in the range of about 5–20 kHz, is given to the workpiece with the help of a piezo actuator and a specially designed fixture. The present work highlights on the possible behaviour of the tool (media) during UAAFM and its effect on the machining process through a computation based approach. Commercially available simulation tool was used to study the effect of the media in response to different set of machining conditions. The responses were evaluated in terms of changes in the fluid pressure, velocity profile of the fluid, temperature distribution in the working fluid and the possible wall shear on the work surface. A three-dimensional model was constructed for simulating the UAAFM process. The simulation shows that the abrasive particles tend to hit the target surface at an angle ‘θ’ which significantly affects the basic mechanisms involved and enhances the effectiveness of the process. The computed wall shear explains that the process will have higher finishing rate and hence the performance. The enhanced interaction of abrasive media in UAAFM while compared to simple AFM could be explained by the resultant pressure–velocity phenomena. Results show that while changes in the amplitude of applied vibration (10 μm and 50 μm) significantly affect the wall shear, the media velocity and pressure profiles are only marginally sensitive to this parameter. The simulation results also confirm that the rise in temperature during the process will not affect the media stability. Results have been discussed vis-a-vis the basic mechanism of the process through suitable illustrations.     

聚氨酯橡胶摩擦轮有限元及疲劳寿命分析

针对汽车滑板输送机聚氨酯橡胶摩擦轮的开裂问题,对摩擦轮与滑板之间的相互作用进行预压紧力和接触摩擦驱动有限元分析,获得摩擦轮的应力和变形分布等结果. 在获得摩擦轮周向应力分布的基础上,根据疲劳裂纹扩展公式对聚氨酯橡胶部分进行疲劳寿命分析,验证是否满足设计要求. 分析过程和结果能为聚氨酯橡胶摩擦轮的详细设计提供参考.     

An analysis method for atomistic abrasion simulations featuring rough surfaces and multiple abrasive particles

We present a molecular dynamics (MD) model system to quantitatively study nanoscopic wear of rough surfaces under two-body and three-body contact conditions with multiple abrasive particles. We describe how to generate a surface with a pseudo-random Gaussian topography which is periodically replicable, and we discuss the constraints on the abrasive particles that lead to certain wear conditions. We propose a post-processing scheme which, based on advection velocity, dynamically identifies the atoms in the simulation as either part of a wear particle, the substrate, or the sheared zone in-between. This scheme is then justified from a crystallographic order point of view. We apply a distance-based contact zone identification scheme and outline a clustering algorithm which can associate each contact atom with the abrasive particle causing the respective contact zone. Finally, we show how the knowledge of each atom’s zone affiliation and a time-resolved evaluation of the substrate topography leads to a break-down of the asperity volume reduction into its components: the pit fill-up volume, the individual wear particles, the shear zone, and the sub-surface substrate compression. As an example, we analyze the time and pressure dependence of the wear volume contributions for two-body and three-body wear processes of a rough iron surface with rigid spherical and cubic abrasive particles.     

聚氨酯橡胶摩擦轮有限元及疲劳寿命分析

针对汽车滑板输送机聚氨酯橡胶摩擦轮的开裂问题,对摩擦轮与滑板之间的相互作用进行预压紧力和接触摩擦驱动有限元分析,获得摩擦轮的应力和变形分布等结果.在获得摩擦轮周向应力分布的基础上,根据疲劳裂纹扩展公式对聚氨酯橡胶部分进行疲劳寿命分析,验证是否满足设计要求.分析过程和结果能为聚氨酯橡胶摩擦轮的详细设计提供参考.     

On the adaptive finite element method of steady-state rolling contact for hyperelasticity in finite deformations

In this paper, we present an adaptive finite element method for steady-state rolling contact in finite deformations along with a residual based a posteriori error estimator for rolling contact problem with Coulomb friction. A general formulation of rolling contact geometry is derived from the point of view of differential geometry. Solvability conditions for the rolling contact problems are discussed. We use Newton's method to solve variational equations derived from a penalty regularization of the finite element approximation of the rolling contact problem. We provide a numerical example to illustrate the method.     

船舶高能搁浅外部动力学的数值仿真研究

基于Simonsen的假设,提出了船舶高能搁浅外部动力学的简化计算公式,并对船舶高能搁浅外部动力学过程进行了数值仿真研究。研究表明,在船舶高能搁浅动力学过程中,有相当部分的初动能转化为旋转形式的动能,包括纵摇、横摇和艏摇;不同于某些船舶碰撞问题,摩擦的影响不能忽略不计;对于船艏高能搁浅的情况,损伤路径会向船体外侧偏离,船舶与礁石之间的接触由剧烈的冲击逐渐过度到侧向挤压和滑动摩擦;相比于简化解析法,数值仿真法可以得到详细的动力学时历结果以及船体结构损伤变形图。     

On the Modeling of Friction and Rolling in Flexible Multi-Body Systems

This paper is concerned with the dynamic analysis of flexible, nonlinear multi-body systems undergoing contact involving friction and rolling. A continuous friction law is used to model the friction forces between contacting bodies. This avoids the numerical problems associated with the discontinuity inherent to Coulomb's friction law and eliminates the need for different sets of equations modeling sliding and rolling as distinct phenomena. On the other hand, continuous friction laws eliminate specific physical phenomena implied by Coulomb's friction law. The condition of vanishing relative velocity between two contacting bodies is not possible: sticking or rolling are replaced by creeping with a small relative velocity. Discrete events such as transition from slipping to rolling or rolling to slipping are eliminated, together with the high frequency phenomena they are likely to cause. The computational issues associated with the continuous friction law and with the enforcement of the non-holonomic rolling constraint are addressed in this paper. This work is developed within the framework of energy preserving and decaying time integration schemes that provide unconditional stability for nonlinear, flexible multi-body systems undergoing contact involving friction and rolling.     

Analysis of demolding in micro metal injection molding

In this paper micro metal injection molding (μMIM) is being studied to produce 316L stainless steel microstructures. Experimental work showed that demolding failure was a serious hindrance to the success of μMIM as a suitable technology to produce small microstructures. Thus, a theoretical analysis of microstructure demolding in μMIM is needed in order to understand the demolding behavior theoretically and how to avoid demolding failure in μMIM. In this paper, theoretical analysis of the demolding of 24×24 (totally 576) microstructures was conducted with the help of Abaqus finite element analysis software. The analysis was involved in two factors that possibly lead to demolding failure: one is the shear stress during ejection of the microstructure due to contact pressure between the microstructure and the microcavity, the other is thermally-induced stress due to cooling of the microstructure. The analysis shows that the following factors have significant influence on the demolding: aspect ratios of the microstructure, the coefficient of friction between the microstructure and the microcavity, demolding temperature and holding pressure. And the microstructure that is farther away from the centerline of the round part with microstructures undergoes higher stress and more easily subject to breakage. The moment when the microstructure is the most possibly subject to breakage during demolding is always the onset of ejection.     

Sensitivity analysis of important parameters affecting contact pressure between a respirator and a headform

Respirator comfort and fit are two important parameters for respirator design, usage, and standard development. The contact pressure (as measured between a respirator and the wearer) plays an important role in comfort and fit. This work attempts to investigate the contact mechanism and factors that affect the contact pressure. This paper focuses on mechanical factors such as strap tension, strap orientation, strap location, friction, and seal material. A finite element (FE) model-based method was developed to assess the contact pressure. The FE models for both the headform and the respirator have multiple layers. The headform is a medium size headform developed by the National Institute for Occupational Safety and Health (NIOSH) and the respirator is an MSA Affinity Ultra respirator. The results show that the positive Z directional force of strap tension that forces the respirator to move towards the headform is the most important parameter for measuring pressure distribution. Other factors such as strap orientation, friction, strap location, and softness of the seal material were found to affect the contact pressure distribution in this study. Strap orientation and friction coefficient have no significant effect on maximum pressure and maximum shear stress. The dispersive strap location increased the contact pressure on the nose-bridge area of the wearer, while concentrated location had no considerable effect on contact pressure. A softer seal material causes larger deformations and transfers the location of the maximum pressure from the nose-bridge to the tip of the nose.

Relevance to industry

This study investigates the effect of important parameters on contact pressure between a respirator and a headform. The sensitivity analysis can provide insights of the interaction between a respirator and a headform. The findings are critical to respirator designers, users, and standard developers to ensure maximal respirator fit and comfort.