钛合金航空紧固件冷镦塑性损伤形成机理研究

Aeronautical fasteners are used to connect the aircraft structure, which are one of the most important fundamental parts in the field of aerospace industry. Aeronautical fasteners of titanium alloy are formed by cold heading. There are many advantages such as: greatly improve the production efficiency and forming precision, and reduce energy consumption and the manufacturing cost. However, there are ductile damage and surface cracking on the aeronautical fasteners in the process of cold heading. These disadvantages weaken the application of the aeronautical fasteners formed by cold heading. As a result, research on the ductile damage evolution mechanism of titanium alloy aeronautical fasteners in cold heading has become an urgent and key basic problem to be solved. In order to solve the above-mentioned problems, based on the continuum damage mechanics theory, this project mainly considers two important parameters of ductile damage, stress triaxiality and lode angle parameter, to establish the multi-scale unified visco-plastic constitutive model of TC16 titanium alloy. In this modelling process, internal state variable model method was used to couple the evolution equations of individual physical variables: ductile damage, dislocation density, stress state, and etc. By using this unified visco-plastic constitutive model, the prediction system of microstructure and ductile damage for aeronautical fasteners will be developed to reveal the ductile damage evolution mechanism of TC16 titanium alloy in cold heading. At the same time, this project investigates the influence of process parameters on ductile damage evolution of TC16 titanium alloy in cold heading. By optimizing the process parameters in cold heading, aeronautical fasteners of high quality will be formed. The results of this research will provide theoretical support and technical guidance for the high efficiency and precision manufacturing of TC16 titanium alloy aeronautical fasteners.

航空紧固件用于飞机机体结构连接，是航空工业领域重要的基础零部件之一。冷镦成形钛合金航空紧固件可以大大提高生产效率与成形精度，并降低能耗与加工制造成本，但冷镦成形紧固件易产生塑性损伤和表面开裂，这严重限制了冷镦成形紧固件的应用。钛合金航空紧固件冷镦塑性损伤形成机理的研究已成为亟待解决的关键基础问题。本项目针对以上问题，基于连续介质损伤力学理论重点考虑塑性损伤两个重要参数（应力三轴度和Lode角参数），采用内部状态变量模型方法耦合塑性损伤、位错密度与应力状态等物理变量的演变方程，建立TC16钛合金多尺度统一粘塑性损伤本构模型，开发紧固件冷镦变形的微观组织与塑性损伤预测系统，揭示TC16钛合金冷镦塑性损伤的形成机理；研究工艺参数对TC16钛合金冷镦塑性损伤演变的影响规律，通过优化工艺参数成形高质量的钛合金航空紧固件。研究成果将为TC16钛合金航空紧固件的高效精密制造提供理论依据与技术指导。

航空紧固件用于飞机机体结构连接，是航空工业领域重要的基础零部件之一。冷镦成形钛合金航空紧固件可以大大提高生产效率与成形精度，并降低能耗与加工制造成本，但冷镦成形紧固件易产生塑性损伤和表面开裂，这严重限制了冷镦成形紧固件的应用。钛合金航空紧固件冷镦塑性损伤形成机理的研究已成为亟待解决的关键基础问题。本项目针对以上问题，基于连续介质损伤力学理论重点考虑了塑性损伤两个重要参数（应力三轴度和Lode角参数），采用内部状态变量模型方法耦合塑性损伤、位错密度与应力状态等物理变量的演变方程，建立了TC16钛合金多尺度统一粘塑性损伤本构模型，开发了一套钛合金冷镦成形航空紧固件的有限元预测系统，揭示了钛合金冷镦成形过程中塑性损伤的形成机制。提出了一套成形TC16钛合金航空紧固件的方案，实现对钛合金航空紧固件的成形精度和性能质量的精密控制，形成稳定的生产线。本项目关键数据包括：TC16钛合金有效断裂应变与应力三轴度、Lode角参数及应变速率的数据关系；钛合金紧固件不同部位塑性损伤形核长大与汇聚分数随变形量、变形速率的演变规律；控制钛合金航空紧固件精密成形的工艺参数。TC16钛合金航空紧固件的试制成功，实现了钛合金在常温下直接快速镦压成形且在不需固溶时效处理的条件下其抗拉强度达1200MPa以上的目标，改变了传统TC4钛合金需要加热后镦压成形与成形后需要固溶时效处理的工艺，起到了节省材料、降低能耗与提高效率及极大降低成本的目的，为铝合金、镁合金等轻质高强合金的研发提供理论参考。