基于热塑性层能分析的高速切削钢轨表面白层形成机理与预测

Thermo-plastic shear wave induced by adiabatic shear instability is a special propagation behavior of adiabatic shear evolution, which has a non-ignorable effect on the formation and transformation of surface hardened layer in high-speed machining. Aiming at the process of high-speed machining in this present research, through microscopic analysis of the interaction mechanism between the propagation of thermo-plastic shear wave induced by adiabatic shear instability and the formation of white layer in the region near to the tool-tip, the pressure and rate related sensitivity characteristics of thermo-plastic shear wave are investigated, and thus the effect mechanism of adiabatic shear on the formation of white layer in high-speed machining is revealed. Based on the thermo-mechanical coupling characteristic in the thermo-plastic shear region, the concept that wave front is treated as moving heat rescore in the propagation of thermo-plastic shear wave is proposed. Through the correlation analysis between the energy distribution on the wave front and its propagation law, the energy convergence characteristic in surface layer during the propagation of thermo-plastic shear wave is obtained and the analysis model of thermo-plastic surface layer energy is built. Considering high-speed machining of rail material under the actual working environment with large feed and high or low temperature, the cutting conditions of white layer formation are predicted and verified. The study results are helpful to promote the application of high-speed machining technology in the high-speed railway maintenance, which supply sufficient experimental and theoretical basises to improve the cutting tool life and the surface integrity.

绝热剪切失稳引发的热塑性剪切波是高速切削过程绝热剪切演化特有的传播行为，对表面硬化层组织的形成和转变所造成的影响不可忽视。本项目针对高速切削过程，通过刀尖附近区域的绝热剪切失稳引发热塑性剪切波的传播对表面白层形成相互作用的微观分析，研究热塑性剪切波对压应力和速率相关的敏感特性，揭示高速切削过程加工表面白层形成的绝热剪切作用机制。根据热塑性剪切区热力耦合的特性，提出波阵面作为移动热源的热塑性剪切波传播思想。通过波阵面能量密度分布与传播规律的相关性分析，获得热塑性剪切波传播过程中能量在表层组织汇聚的特性，建立热塑性层能分析模型。考虑钢轨材料大进给量高速切削过程，及高温高寒等实际作业环境，对白层组织形成的切削条件进行预测与实验验证。研究结果将促进高速切削技术在高速铁路养护过程中的应用，对刀具寿命的提高和表面完整性的改善奠定充分的实验和理论基础。

高速切削过程绝热剪切失稳引发的热塑性剪切波是绝热剪切演化特有的传播行为，直接影响加工表面白层组织的形成。通过高速切削实验和微观分析实验，获得了加工表面组织演化历程的金相显微照片，揭示了刀尖附近热塑性区的传播效应对加工表面白层形成的压应力和速率相关作用机制；提出了热塑性剪切波传播形成加工表面的基本思想，推导了加工表面白层形成临界条件的力学判据和白层组织转变程度的表达式，揭示了热塑性剪切波传播过程表层能量的梯度分布特性规律，构建了加工表面热塑性层能分析理论；考虑高速切削钢轨材料实际作业环境，根据热塑性层能分析理论、动态塑性本构关系、热塑性剪切变形条件与切削条件的耦合关系，建立了高速切削过程加工表面白层形成临界切削条件的预测模型。结果表明：加工表面白层形成的临界切削速度随刀具前角的增大、进给量的增大而增大。具有较高的密度、较大的比热容和导热系数、较高的热软化效应的材料，在负前角刀具和小进给量条件下越容易形成白层组织。本项目研究结果有助于深入理解绝热剪切演化行为对表面完整性的影响，为满足高速切削技术在铁路养护过程中的应用需求提供坚实的理论和技术基础。