自动钻铆多历史应力统一特征及损伤衍变的疲劳机理

Technologies producing long-life joints are badly in need for the manufacturing of the new generation of military aircraft. For that, it is becoming a trend the automatic drilling and riveting (ADR) technology taking the place of the traditional drilling and riveting method in the modern airplane manufacturing process. However, the application of ADR technology requires some new concerns for the fatigue properties of the rivet joint as it is distinguished with the traditional method. As a result, this project is dedicated to studying the influence of automatic drilling and riveting process on the fatigue properties of airplane structures. As the study of residual stress and its influence on fatigue properties are usually carried out separately for drilling and riveting in present works, the influence of drilling on riveting is treated idealized or ignored. Therefore, error is usually inevitable in these models. To perform a more reliable study, we come up with the idea to build a unified stress field model following the mainline of the change of residual stress during the ADR process taking into account the influence between each historical stage. The work is focused on three key points: residual stress model for drilling and riveting process, burr model for drilling based on the mechanism of cutting material, and the evolution of damage and strengthening effect during fatigue in the framework of unified residual stress field. In detail, the residual stresses resulted from different historical stages is to be studied by theoretical modeling and experimental test. After that, a unified stress field model is to be built taking into account the influence of stresses between different stages on the basis of constitutive relation and plastic deformation theory of the material. Finally, on the basis of characteristics of drilling-resulted burr, the stress-based damage mechanism of the material and the competitive mechanism between strengthening and weakening resulted from the beneficial and detrimental component of residual stress are to be investigated, leading to the final goal of this project which is to build a unified historical stress model and to predict the fatigue life of riveted structure upon a controlled drilling quality. The findings of this project will greatly add to the knowledge of ADR technology for process optimization and moreover, enhance the technical level of aircraft manufacturing in China.

针对我国新一代军用飞机制造领域对长寿命连接技术的迫切需求以及自动钻铆技术逐步取代传统手工钻铆所带来的新问题，本项目旨在系统深入地开展自动钻铆对飞机结构的疲劳特性影响机理研究。以自动钻铆过程中残余应力的变化为主线，研究制孔、装配过程中各环节导致的残余应力的理论分析方法和检测技术，以材料的本构关系和塑性变形理论为基础，考虑各阶段历史应力之间的互影响耦合关系，建立统一的应力场描述模型。重点解决钻铆过程应力场的描述模型、基于刀具与材料相互作用的制孔毛刺模型、多历史应力下损伤与强化特征衍变的结构疲劳特性等基础理论问题。在制孔毛刺特征的基础上，考察基于力的材料损伤衍变机理，研究残余应力有害分量与有益分量的损伤与强化竞争机制，解决基于可控的制孔初始质量的钻铆多历史应力统一性描述及结构疲劳寿命评估问题，为飞机自动钻铆工艺优化提供理论基础，提升我国飞机制造技术水平。

本项目针对我国新一代军用飞机制造领域对长寿命连接技术的迫切需求以及自动钻铆技术逐步取代传统手工钻铆所带来的新问题，探索了不同工艺条件下铆接装配结构的力学性能。基于塑性成形原理与弹塑性力学理论建立了铆接力与钉头成镦头尺寸关系模型，进一步建立了铆接力与初始配合容差共影响下的钉/孔变形力学模型；通过Abaqus有限元仿真软件建立了2D轴对称有限元铆接模型，分析了不同钉头尺寸以及初始配合条件下的带孔板应力/应变特征；基于3D有限元模型分析了多排铆钉搭接接头的铆接及拉伸作用下的应力特征，通过用户自定义单元编程实现了铆接残余应力与二次弯曲效应共同作用下的裂纹尖端应力强度因子的计算，并用其对裂纹的扩展速率进行分析；通过试验研究了不同工艺特征下铆接搭接接头裂纹萌生与裂纹扩展特征、断裂特征以及疲劳寿命，基于等效疲劳寿命的方法验证了Elber裂纹张开（闭合）应力模型对包含残余应力作用的铆接接头疲劳分析的有效性。本项目成果完善了自动钻铆质量评估体系，为我国新一代飞机长寿命连接的工业化应用提供工艺解决方案。