【作者】 胡兆稳；

【导师】 刘焜；

【作者基本信息】 合肥工业大学 ， 机械设计及理论， 2013， 博士

【摘要】 塑性变形界面广泛存在于金属塑性成形中，此时工件、模具和润滑剂构成了一个复杂的摩擦学系统。论文研究了混合润滑状态下塑性变形界面微凸体平坦化行为，以期更好地理解塑性成形中工件表面形貌的演化和界面摩擦行为，为产品表面质量和界面摩擦性能的控制提供理论依据。基于机械流变模型和ISO25178三维表面参数，研究了微凸体平坦化引起的表面形貌变化的表征问题。运用图像数学形态学处理技术，有效地实现了封闭润滑油坑特征和基于机械流变模型的三维表面形貌参数的提取，以及真实接触面积比的确定。采用有限元法，建立了模具与工件粗糙表面接触模型，分析了接触压力、基体塑性应变、界面摩擦和微凸体角度等因素对微凸体平坦化的影响。结果表明，真实接触面积比随着基体塑性应变和接触压力的增加而增加；界面滑动摩擦有利于微凸体平坦化，但其促进效应无法与基体塑性应变和接触压力相比；微凸体平坦化阻力随着其角度的增加而增加，但增加趋势逐渐减缓。铝材压缩实验结果证明了有限元模拟的有效性。分别在有、无润滑条件下进行了不同表面纹理结构的1050铝材平面应变压缩实验；对表面形貌进行了测量和分析，研究在不同载荷和基体应变条件下微凸体平坦化行为和表面形貌结构的变化；基于封闭润滑油坑演化和微凸体平坦化行为的关联性分析，来理解静态有润滑接触条件下表面纹理结构对微凸体平坦化行为的影响；采用ISO25178三维表面参数和基于机械流变模型的三维表面参数，对工件表面形貌进行了表征，来描述微凸体平坦化引起表面形貌的变化。在自制的塑性成形摩擦测试装置上进行了带材拉伸实验，来研究滑动接触条件下不同纹理结构表面的微凸体平坦化行为、表面形貌结构变化以及界面摩擦特性。实验结果显示，摩擦系数表现出压力和速度的依赖性，且与封闭润滑油坑的演化相关联。研究了算术平均偏差、最快衰减自相关长度、表面纹理特征比、表面展开面积比和表面均方根斜率等三维表面参数随名义接触压力和拉伸速度的变化。基于机械流变模型，分析了润滑机制、微凸体平坦化引起表面形貌变化、载荷承载机理和界面摩擦特性间的内在联系，从而揭示了微凸体平坦化行为对界面摩擦的影响；并探讨了最大封闭空面积比表征界面摩擦性能的有效性。在考虑塑性变形界面封闭润滑油坑中润滑剂陷入和逃逸行为的条件下，分别建立了静态和滑动有润滑接触过程中规则表面微凸体平坦化的理论模型，分析了接触条件对微凸体平坦化的影响，并初步验证了微凸体平坦化模型的有效性。提取封闭润滑油坑特征，并分析封闭润滑油坑的演化和三维表面形貌参数与混合润滑状态下微凸体平坦化行为的关联性，是本论文的主要创新之处。论文研究结果对产品表面质量和界面摩擦性能的控制有理论指导意义。更多还原

【Abstract】 The plastic deformed interface widely exists in metal forming process, at which the surfacetopography of workpiece and tool, lubricant form a complex system. In this dissertation, in order togain a better understanding of the evolution of workpiece surface topography and to provide atheoretical basis for the control of surface quality of products and the interfacial friction, thebehaviour of asperity flattening of workpiece surface at plastic deformed interface in mixedlubrication regime is studied.Based on mechanical-rheological model and the three dimensional surface parameters definedin ISO25178, the characterization of the changes of surface topography resulting from asperityflattening is investigated. Using mathematical morphology image processing technology, theextraction of closed lubricant pockets features and the three dimensional surface parameters derivedfrom mechanical-rheological model and the assessment of real contact area ratio are achievedeffectively.A finite element model for rough surface contact between tool and workpiece is developed.Theeffects of the contact pressure, bulk plastic strain, interfacial friction and asperity angle on asperityflattening are analysed in detail. The results show that the real contact area ratio increases with thecontact pressure and bulk plastic strain. The contribution of interfacial sliding friction to asperityflattening is not comparable to that of bulk plastic strain as well as contact pressure. The resistanceof asperity to flattening increases with increasing asperity angle, but the increasing rate decreases.The experimental results of compression tests on aluminium samples show the validity of the finiteelement simulation.A series of plane strain compression tests on aluminium1050sheet specimens with differenttypes of texturing topographies are conducted with lubricantion and without lubricantionrespectively. Measurement and alalysis of the surface topagraphy of the specimens are performed toinvestigate the asperity flattening behaviour and variations of surface microstructure for variousloads and bulk strains. Based on the correlation analysis between the evolution of the closedlubricant pockets and the behaviour of asperity flattening, the effect of surface topography on theasperity flattening in static contact process is discussed. By using the three dimensional surfaceparameters defined in ISO25178and derived from mechanical-rheological model respectively, thecharacterization of surface topography is achieved to describe the changes of surface microgeometryinduced by asperity flattening. In order to investigate the asperity flattening behaviour and the changes of surfacemicrostructure as well as the frictional performances at plastic deformed interface in sliding contactprocess, a novel metal forming tribometer is built up and used to perform a series of strip drawingtests.It is found that the coefficient of friction shows a dependence on contact pressure and drawingvelocity when drawing velocity and contact pressure remains constant respectively, which can berelated to the evolution of closed lubricant pockets. The variations of surface microstructure withnominal contact pressure and drawing velocity are characterized by such three dimensional surfaceparameters as arithmetical mean height, the fastest decay autocorrelation length, texture aspect ratio,developed interfacial area ratio and root mean square slope of the surface. Based onmechanical-rheological model, the internal relationship between the lubrication regime, thevariations in the surface microstructure, the load bearing mechanism and the interfacial friction isstudied to reveal the influnce of asperity flattening on the interfacial friction. The applicability of themaximum closed void area ratio for a description of the friction performances in metal formingprocess is analyzed.Considering entrapment and escape of liquid lubricant in closed lubricant pockets at plasticdeformed interface, theoretical models for asperity flattening of workpiece surface with a regulararray of wedges for static contact and sliding contact respectively are developed. The effects ofdifferent contact conditions on surface asperity flattening are analyzed in detail. The validity of thetheoretical models of asperity flattening proposed is verified primarily.An important innovation in this dissertation is to extract the closed lubricant pockets featuresand to relate three dimensional surface parameters and the evolution of closed lubricant pockets tothe behaviour of asperity flattening at plastic deformed interface in mixed lubrication regime. Studyresults will be beneficial to improve theoretically the control of surface quality of products andinterfacial friction.更多还原