GFRP/Al-Li复合层板喷丸成形与服役过程的残余应力演变及对变形的影响机理

Fiber-metal super hybrid laminates has been treated as the crucial materials for skin structure of large aircraft owing to its excellent fatigue and impact properties. However, its application is limited by the difficulty in laminates forming as a result of the complicated interface structure and limited failure strain. This research investigates the residual stress evolution and its influence mechanism on the deformation behavior of GFRP/Al-Li super hybrid laminate in shot peen forming, serving for the large plane project of China. Firstly, the generation, evolution and distribution characteristics of the residual stress during the laminates forming are investigated, in view of the essential problem of “stress dominant deformation” in shot peen forming. Then, the deformation behavior of the laminates during shot peening is studied, focusing on the interactions and related mechanism between residual stress and defamation. Furthermore, considering the service characteristics of the aircraft skin, the residual stress evolution and its influence mechanism on the deformation behavior of GFRP/Al-Li laminates subjected to the alternating temperature also analyzed, as the residual stress of the laminate always varies with temperature. This project aims to reveal the shot peen forming mechanism of super hybrid composites, thus provide theoretical foundation for its deformation prediction and control, facilitating the shot peen manufacturing of GFRP/Al-Li super hybrid laminate and its application on large aircraft.

纤维-金属超混杂复合层板具有优异的抗疲劳和耐冲击性能，是大型飞机蒙皮结构的重要选材。但该类层板存在复杂的界面且纤维层的破坏应变小，成形难度大，是制约其应用的主要因素。本项目基于我国启动的大飞机工程，针对GFRP/Al-Li超混杂复合层板，研究其喷丸成形与服役过程的残余应力演变规律及对变形的影响机理。首先，围绕喷丸成形中“应力主导变形”的核心问题，探索喷丸应力的形成及演变机制，揭示残余应力的分布特征；并在此基础上，研究该层板在喷丸成形中的变形行为，着重探讨残余应力与变形间的作用机理。同时，结合该层板残余应力随温度而变化的特点，基于飞机蒙皮结构的服役特征，开展其在交变热场下的残余应力演变规律及对变形的影响机制研究。通过本项目的研究，将进一步揭示超混杂复合层板的喷丸成形机理，为该材料喷丸变形的预测与调控提供理论依据，对推进超混杂复合层板的喷丸成形制造及在大飞机上的应用具有积极意义。

纤维金属超混杂复合层板具有优异的抗疲劳和耐冲击性能，是大型飞机蒙皮结构的重要选材。但该类层板存在复杂的界面且纤维层的破坏应变小，成形难度大，是制约其应用的主要因素。本项目面向我国启动的大飞机工程，针对GFRP/Al-Li超混杂复合层板，研究了其喷丸成形与服役过程的残余应力演变规律及对变形的影响机理。首先，围绕喷丸成形中“应力主导变形”的核心问题，探索了喷丸应力的形成及演变机制，揭示了其固化及喷丸成形后的残余应力分布特征；在此基础上，研究了该层板在喷丸成形中的变形行为，着重探讨了残余应力与变形间的作用机理。同时，结合该层板残余应力随温度而变化的特点，基于飞机蒙皮结构的服役特征，开展了其在交变热场下的残余应力演变规律及对变形的影响机制研究。研究结果表明，结合X射线、去层腐蚀、光栅光纤监测等方法，可实现GFRP/Al-Li超混杂复合层板残余应力的有效评价。单个弹丸作用于金属层表面形成的局部塑性变形特征及形成的应力场受到纤维方向和固化残余应力的影响，且影响规律因弹丸大小和冲击能量而异。弹丸的动态冲击相比于准静态压入将会在层板表面金属层引入更大的残余应力。基于优化的有限元模型，通过模拟多弹丸动态冲击过程，可将喷丸变形量的预测误差缩小至20%以内，即基本建立了喷丸参数与喷丸变形间的关系。此外，由于金属及纤维层的应力变化使得层板内部产生附加弯矩，在100℃温度变化范围内，层板会出现1%以内的变形。经历1100次-55-100℃的热疲劳循环，GFRP/Al-Li层板内部残余应力发生松弛，层板产生微小变形，但弧高变形量最大值均在5%以内。通过本项目的研究，进一步揭示了超混杂复合层板的喷丸成形机理，为该材料喷丸变形的预测与调控提供了理论依据，对推进超混杂复合层板的喷丸成形制造及在大飞机上的应用具有积极意义。