由于摩擦磨损过程的复杂性，传统的检测方法很难实时在线表征摩擦接触区的局部特性和微观机制。声发射检测技术是一种在线动态无损的检测技术，可用于检测和表征材料损耗的微观特性和机制，因此该技术已被用于摩擦磨损状态检测，然而现有研究多使用声发射对摩擦过程进行定性描述，对摩擦过程的声发射机制认识不足。本文对典型金属材料划痕过程中的声发射特性进行系统研究，探索划痕过程中金属材料形变和损伤的声发射机制，为基于声发射技术的摩擦磨损状态在线检测和机理研究奠定了基础。主要研究工作和结果如下： 为有效分析和挖掘划痕过程中的声发射信号特性，采用遗传算法对Morlet小波参数进行优化，研究并改进了基于Morlet小波的连续小波变换尺度谱分析方法，显著提高了小波尺度谱的时频分析能力；其次针对辨识和分离声发射信号中瞬态成分的需求，对比研究了多种谱峭度计算方法，获得了适用于分析和挖掘声发射瞬态特性的谱峭度分析方法，为后续研究中辨识和分离不同特性的声发射信号提供了新的有效手段。 根据不同的塑脆性能，选择四种典型金属材料Cu、Ni、Mo和W作为研究对象。通过划痕实验，对比分析了摩擦系数和声发射参数表征载荷及速度的有效性，结果表明声发射参数比摩擦系数更灵敏，更能体现接触区的微观变化。 通过划痕实验对Cu和Ni划痕形变的声发射特性进行了研究，发现了对于声发射典型塑性金属材料存在特征应变速率的规律：当应变速率低于特征应变速率时，声发射强度与应变速率呈正相关，当应变速率高于特征应变速率时，声发射强度与应变速率呈负相关。并基于位错运动理论，对上述规律进行了深入分析，揭示了其机理，研究结果印证了接触区闪温对材料性能和摩擦特性的影响，同时也为基于声发射进行的摩擦磨损机理研究提供了依据。 此外，本文研究了Mo和W不同划痕损伤的声发射特性，通过小波尺度谱方法分析了声发射信号的时频特性，辨识了划痕损伤过程中的声发射源。结果表明，Mo划痕过程中的冲击信号是由断裂产生的，而连续信号是由塑性撕裂产生的；W划痕过程中的声发射信号只包含由断裂产生的冲击信号。该研究结果对基于声发射的划痕损伤形式及形成机理研究具有重要意义。

Due to the complexity of tribological phenomena, the understanding of friction and wear process is currently insufficient, and many problems concerning friction and wear are far from resolution. In this way, monitoring friction and wear process is highly significant and provides critical information regarding friction. For this reason, a new method of providing a direct and unambiguous indication of friction and wear condition would be extremely valuable. Acoustic emission (AE) is a non-destructive and on-line testing method, which has been widely used in fault diagnosis. AE signals detected in friction and wear process include a large amount of information related to tribological phenomena. This is because AE is directly caused by the deformation and fracture of machine parts. Most of the current researches give some qualitative results, but the AE mechanisms in the friction and wear process still need to be further studied. In this work, the AE characteristics in scratching of typical metals are systematically investigated, and the AE mechanisms of the scratch deformation and scratch damage are also explored. The main work and achievements of this paper are shown as follow: The wavelet scalogram of the continuous wavelet transform is studied with simulation experiments, the Morlet wavelet is selected to be the wavelet base, and the parameters of Morlet wavelet are optimized by genetic algorithm (GA), which significantly improves the time-frequency performance of the wavelet scalogram analysis. The calculation methods of spectral kurtosis are introduced, and the ability of different spectral kurtosis methods to describe the transient characteristic of AE signal are investigated. The spectral kurtosis method provides a new way for the identification and separation of different AE characteristics.According to the different plastic and brittle properties, four typical metal materials Cu, Ni, Mo and W, are selected as the research objects. The validities of the friction coefficient and acoustic emission to characterize the load and velocity are compared and analyzed. The results show that the acoustic emission parameters are more sensitive to the scratch process than the friction coefficient.The scratch tests are used to study the plastic deformation and AE characteristics during the scratch process of Cu and Ni. It is found that the typical metals have a characteristic strain rate, when the starin rate is lower than this characteristic strain rate, the AE intensity is positively correlated with strain rate, and when the starin rate is higher than this characteristic strain rate, AE intensity is negatively correlated with strain rate. A dislocation motion model is constructed to describe the released energy from dislocation motion under the effect of stress and strain rate. Based on the theory of dislocation motion, the variation of AE with the strain rate are analyzed, and its mechanism is also revealed. These research results confirm the effect of flash temperature in the contact area on the mechanical properties and friction characteristics of the material, and also provide a theoretical basis for the condition monitoring of friction pairs using AE method.The AE characteristics of Mo and W with different scratch damages are also studied. The results show that the typical AE signals from Mo are composed of continuous waveforms and bursts, the continuous waveforms are generated due to the ductile tears, while the bursts are generated due to the cracks. The typical AE signals from W only have bursts, which are generated due to the cracks. AE signals can identify the different scratch damage types of Mo and W, and these results have important significance for the monitoring of friction damage using AE method.