考虑时变几何形貌与动态材料本构的船用发动机轴瓦磨合摩擦机理研究

The running-in process of marine engine bearing bush has a great influence on the tribological performance after service. The running-in process is in the state of mixed lubrication. The time-varying surface morphology induced by the wear and plastic deformation is an important feature. The temperature and strain rate in the contact zone undergo a two-dimensional space-time evolution, resulting in a dynamic change of the material constitutive. In order to study the friction mechanism of the bearing bush during the running-in process with time-varying geometrical morphology and dynamic material constitutive, this project constructs the molecular dynamics model of the crankshaft/bushing friction pair, which has the specific materials used in the marine engine, and reveals the dynamic wear mechanism of the bearing bush. The quantitative mapping relationship between wear and working parameters is also established. The law of the change of the bearing material constitutive with temperature and strain rate during the friction process is studied. A dynamic constitutive model suitable for the service environment of bearing bush is established, and the effect of the constitutive parameters on the contact plastic deformation on microscopic is investigated. Then the time-varying mechanism of surface morphology is revealed. A thermo-fluid-solid coupling micro-transient mixed-lubrication analysis method is established to investigate the coupling mechanism between the dynamic change of the three-dimensional topography, the material constitutive relation of the bearing bush and the mixed lubrication process during the running-in phase, and to analyze the sensitivity of the constitutive parameters to the effects of mixed lubrication characteristics. The experimental verification is carried out to provide theoretical model. This project can apply the guidance for improving the tribological performance of the bearing bush during the running-in process.

船用发动机轴瓦磨合过程对其服役后的摩擦学性能影响重大。磨合过程处于混合润滑状态，磨损和塑性变形诱发表面形貌时变是其重要特征，而接触区温度和应变率也在时间域和空间域内发生二维演变，导致材料本构关系随之动态变化。为阐释具有时变几何形貌、动态材料本构等特征的轴瓦磨合阶段摩擦机理，本课题构建船用发动机曲轴/轴瓦摩擦副特定材料的分子动力学模型，揭示轴瓦磨损的动态机制，并建立磨损与工况参数间的定量映射关系；研究摩擦过程中轴瓦材料本构关系随温度、应变率变化的规律，建立适用于轴瓦材料服役环境的动态本构模型，探究本构参数对微观接触塑性变形的影响；进而阐释表面形貌的时变机制。建立热-流-固耦合微观瞬态混合润滑分析方法，探究轴瓦三维形貌和材料本构关系动态变化与磨合阶段混合润滑过程之间的耦合作用机理，分析本构参数对混合润滑特性参数影响的敏感性，并进行实验验证。本课题可望为改善轴瓦磨合阶段摩擦学性能提供理论指导。

为进一步阐释船用发动机曲轴-轴瓦摩擦副磨合过程中摩擦学特性，本项目采用分子动力学方法探究了曲轴-轴瓦摩擦副特定材料微观摩擦学机理，从分子层面阐释了载荷、温度等不同条件对轴瓦摩擦学特性参数的影响规律，进而为获取后续混合润滑状态下固体摩擦系数及磨损系数等特征系数提供理论支撑；基于准静态拉伸试验和霍普金森压杆试验，分别测试轴瓦合金材料在不同温度和不同应变率下的真实应力应变曲线，获取轴瓦合金材料动态本构特征，并采用不同本构模型进行拟合，确定最适合描述轴瓦合金材料本构关系的模型；基于所确定的动态本构模型，建立微观合金微观接触模型，获取不同工况（速度、间隙）、不同本构模型参数下的接触温升、接触载荷、摩擦系数等接触特性参数的变化规律，进而为轴瓦合金材料本构模型参数优选提供理论支撑；耦合船用发动机曲轴-轴瓦摩擦副混合润滑过程中的实时磨损特征，考虑轴瓦表面形貌变化，形成了相应的混合热弹性流体动压润滑预测方法，并通过采用轴向变壁厚设计，减小边缘承载及过度磨损。该项目可深化对轴瓦磨合等不同阶段混合润滑状态的认识，提升对船用曲轴-轴瓦摩擦副润滑与磨损的定量预测能力。