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活塞环-缸套系统摩擦润滑过程产生的声发射信号是湮没在强背景噪声下的非稳态弱信号,特征难以提取和分析.为了有效抑制强噪声,提出一种基于信号物理特征的自适应阈值小波包降噪算法.根据小波包时频分析确定摩擦声发射的最佳特征提取频段,构建基于活塞速度廓形曲线的自适应小波包阈值函数,实现了对表征摩擦润滑的声发射信号的有效提取.将该算法用于分析发动机燃烧试验测得的声发射信号.使用三种不同润滑油(10W30、15W40和旧机油)验证算法的有效性.结果 表明,该算法能有效地抑制由阀门开关、燃烧和喷油过程产生的大幅值的噪声.声发射特征值随着润滑油的黏度增大而增大,含有颗粒物的旧机油的声发射特征值随着转速的增大而明显增大.为实现在线监测和诊断活塞环-缸套系统健康状态进而评估润滑油的品质提供了可行的方法. 相似文献
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利用声发射技术监测螺栓工作过程中的状态变化,对声发射检测信号进行时域、频域及小波分析。结果表明,螺栓由于塑性变形和断裂引起的声发射频率明显区别于振动、撞击、摩擦等所产生的频率,验证了声发射技术用于连接螺栓状态辨识的可行性。 相似文献
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金属切削过程中产生丰富的声发射。用声发射技术监测切屑状态是一个很有潜力的新方法。本文通过实验研究了车削时切屑状态和声发射信号间的相互关系,结果表明:1.声发射DC包络信号脉冲能准确反映断屑情况;2.声发射加权计数率波形和包络信号均值能反映切屑形状和异常切屑状态;3.不同类型切屑的形成过程具有不同的声发射信号波形。 相似文献
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声发射(Acoustic Emission)是固体材料在塑性变形及开裂过程中以弹性波的形式释放应变能的一种物理现象。这种现象已成功地在无损检测中用以检测构件或材料内部的缺陷。在磨削加工中,当砂轮与工件接触时,由于砂粒与工件的摩擦和金属的塑性变形与剥离也产生强烈的高频声发射信号,其频率在50kHz到1MHz之间。信号的时域和频域结构与砂轮和工件的接触状况、砂轮表面形貌和磨削过程有关。利用声发射信号进行磨削过程控制和机理研究具有灵敏度高、不受低频振动干扰的优点。通过磨削过程的声发射信号研究,揭示其相关性,可以为磨削过程控制提供一种新的途径。 相似文献
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The friction and wear behaviors of polyamide 66 (PA 66) and rubber-filled PA 66 (PA 66/SEBS-g-MA) composites were investigated on a block-on-wheel model friction and wear tester under dry sliding and water lubricating conditions. In order to further understand the wear mechanisms, the worn surfaces and scraps of samples were analyzed by scanning electron microscopy (SEM) and differential scanning calorimeter (DSC). The experimental results indicated that the wear mass loss and the friction coefficient of PA 66 decreased with the addition of rubber particles. The friction coefficients of PA 66 and PA 66/SEBS-g-MA composites under water lubricating condition are lower than those under dry sliding condition, but the wear mass losses are higher than those under dry sliding condition. The main wear mechanisms under dry sliding condition are the plastic deformation and mechanical microploughing. Whereas the main wear mechanisms under water lubricating condition are the mechanical microploughing and abrasive wear. 相似文献
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The initial scratching of soft metals by relatively hard metallic asperities involves considerable plastic deformation and wear of the harder metal. Thus the penetration effect on friction is reduced successively as sliding proceeds, leading to the shearing type of friction. Such a transition state of sliding can be defined as a quasi-scratch friction process because ploughing precedes the steady sliding condition.The deformation and wear behaviour at a friction junction was investigated using model experiments between a mild steel conical rider and a flat copper surface. Changes in geometry of the rider and pile-up of the flat metal were examined metallographically and with a microscope. It was found that a stable value of the friction force is determined from the geometric shape of the junction attained after the completion of transient sliding and the effect of initial asperity shape on the friction force becomes insignificant. 相似文献
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In the analysis of metal forming processes, a knowledge of friction is important, especially when the microstructure evolution and criteria for limiting phenomena are predicted by numerical simulation. The friction wave model has been studied by several researchers. Their analyses are mainly based on the assumption that there is no plastic deformation of the bulk material. However, it is necessary to clarify the influence of bulk material deformation on the surface asperity deformation. This paper deals with the development of a friction wave model by considering the influence of bulk material on the surface asperity deformation. The situation of rough tool—smooth workpiece (RT—SW) contact during forming process has been investigated. Based on this condition, an admissible velocity field is constructed for the upper bound analysis. The relationship between the normal pressure and the sliding resistance is established over a large range of pressure. The role of surface roughness, bulk displacement and bulk strain on metal forming friction is analysed. 相似文献
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Eui Gyun Na Kanji Ono Dong Whan Lee 《Journal of Mechanical Science and Technology》2006,20(2):197-204
The purpose of this study is to evaluate the AE characteristics for the basemetal, PWHT (post-weld heat treatment) and weldment
specimens of SA-516 steel during fracture testing. Four-point bending and AE tests were conducted simultaneously. AE signals
were emitted in the process of plastic deformation. AE signal strength and amplitude of the weldment was the strongest, followed
by PWHT specimen and basemetal. More AE signals were emitted from the weldment samples because of the oxides, and discontinuous
mechanical properties. AE signal strength and amplitude for the basemetal or PWHT specimen decreased remarkably compared to
the weldment because of lower strength. Pre-cracked specimens emitted even lower event counts than the corresponding blunt
notched specimens. Dimple fracture from void coalescence mechanism is associated with low-level AE signal strength for the
basemetal or PWHT. Tearing mode and dimple formation were shown on the fracture surfaces of the weldment, but only a small
fraction produced detectable AE. 相似文献
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L. V. Zolotukhina A. Ya. Zapevalov S. V. Zhidovinova I. G. Arefyev B. R. Gel’chinskii 《Journal of Friction and Wear》2011,32(2):107-112
It is demonstrated that the wear rate of tribocouples can be reduced significantly with the use of lubricating compositions
obtained by added super- and nanodispersed zinc or Cu-Sn powders to the Lithol-24 plastic grease. When the superdispersed
powders of copper alloys interact with tribosurfaces, the copper and tin diffuse into the base metal, producing secondary
composite superdispersed structures. The alloyed elements penetrate into the base metal more deeply if the powder contains
the nanodispersed fraction. The films of polyfluorinated oligomers based on particles of zinc and copper alloy powders with
functional substitutes reduce substantially the friction coefficient of kinematic couples when they are lubricated with these
lubricating compositions and expand the temperature range of application of plastic greases. 相似文献
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模具粗糙度对板材拉延件摩擦特性的影响 总被引:3,自引:0,他引:3
金属板材拉延是一个复杂的塑性变形过程,广泛应用在各种大型汽车覆盖件等零件生产中。介绍了金属带料弯曲拉伸试验机的工作原理和试验方法。该试验机能很好地模拟凹模圆角区的摩擦场变化规律;通过选用不同的模具表面粗糙度,改变带料拉伸力、变形速度和成形头平均面压,测出摩擦因数的变化规律,用以研究模具表面粗糙度等对板材拉延件摩擦特性的影响。研究表明,适当降低模具表面粗糙度,有利于发展边界润滑,减少摩擦热的产生和作用。该研究方法把拉延过程中的摩擦、磨损和润滑有机地结合起来,为优化拉延件加工的摩擦条件奠定了理论基础。 相似文献
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The friction characteristics of lubricated electrical sliding contacts are considered. Data are presented concerning the effects of the current, the lubricant properties, the velocity and the load on the friction and wear behaviour of the contacts. In light-current electrical contacts the effectiveness of the lubricant does not depend on its conductivity but on its ability to prevent the formation of a non-conductive film by lubricating action. Under semifluid lubricating conditions the heavy current acts by discharge through the lubricant film, and the lubricant conductivity generally determines the friction and wear characteristics of the contact. Colloidal metal particles produce additional conductivity in the clearance between the contacting surfaces, prevent electrical erosion and, in some cases, form plastic films which decrease the coefficient of friction and the wear rate of the contact. 相似文献
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Md. Sayem Hossain Bhuiyan Imtiaz Ahmed Choudhury Nukman Yusoff 《The International Journal of Advanced Manufacturing Technology》2012,61(5-8):465-479
The industrial demand for automated machining systems to enhance process productivity and quality in machining aerospace components requires investigation of tool condition monitoring. The formation of chip and its removal have a remarkable effect on the state of the cutting tool during turning. This work presents a new technique using acoustic emission (AE) to monitor the tool condition by separating the chip formation frequencies from the rest of the signal which comes mostly from tool wear and plastic deformation of the work material. A dummy tool holder and sensor setup have been designed and integrated with the conventional tool holder system to capture the time-domain chip formation signals independently during turning. Several dry turning tests have been conducted at the speed ranging from 120 to 180?m/min, feed rate from 0.20 to 0.50?mm/rev, and depth of cut from 1 to 1.5?mm. The tool insert used was TiN-coated carbide while the work material was high-carbon steel. The signals from the dummy setup clearly differ from the AE signals of the conventional setup. It has been observed that time-domain signal and corresponding frequency response can predict the tool conditions. The rate of tool wear was found to decrease with chip breakage even at higher feed rate. The tool wear and plastic deformation were viewed to decrease with the increased radius of chip curvature and thinner chip thickness even at the highest cutting speed, and these have been verified by measuring tool wear. The chip formation frequency has been found to be within 97.7 to 640?kHz. 相似文献
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A. N. Bolotov V. V. Meshkov O. V. Sutyagin M. V. Vasiliev 《Journal of Friction and Wear》2013,34(1):1-5
A method for the engineering calculation of the critical loads that govern the origination and development of plastic deformation during the contact of a spherical indenter has been proposed as applied to the friction of metals and solid lubricating coatings. The available approaches to the investigation of elastoplastic contact deformations have been verified using the finite element method. The effect of a low-modulus coating on the origination of plastic deformations of the base has been shown. 相似文献