冲击载荷下CFRP干涉螺接构件拉剪损伤演变机理研究

Light-weight design is an important topic in the development of aircrafts, especially large aircrafts. Hence, carbon fiber reinforced polymer (CFRP) is widely used in aviation field. Bolted joining techniques are the dominant joining methods currently used in composite structures. However, due to the poor dynamic resistance and possible damage, CFRP bolted joints have restricted the improvement of aircraft failure behaviors in a crash situation. Interference fit is proved to significantly increase the fatigue life and static strength of CFRP bolted joints, however, the effects of interference fit on the dynamic damage behaviors of CFRP bolted joints are still unknown. Therefore, the bearing and shear damage evolution mechanism of CFRP interference fit bolted joints under dynamic loading are studied in this project. The testing method based on electromagnetic dynamic force is firstly developed, and the damage mechanism and damage accumulation progress of CFRP interference fit bolted joints are investigated. The effects of micro damage on the macro mechanical responses are also discussed. Then, the damage prediction model considering strain rate and inertial effects is developed, and the stress distributions caused by interference fit and dynamic loading are studied with different interference sizes and loading rates. Moreover, the relationships between the dynamic damage behaviors and the stress distributions are presented. Finally, strengthening strategies to improve the dynamic damage resistance of CFRP bolted joint are given through the study results, which can provide a reliable basic theory and useful design method for the improvement of aircraft failure behaviors in a crash situation.

轻量化是飞机尤其是大型飞机研制的重要主题，为此碳纤维增强复合材料（CFRP）被广泛应用。螺接是飞机CFRP结构最主要的连接方式，但CFRP螺接构件抗冲击性能差、易损伤，成为制约飞机复合材料结构可靠性提升的瓶颈。干涉连接能显著提高CFRP螺接构件疲劳寿命和静强度，但对冲击损伤行为的抑制机理尚不清楚。因此，本项目以CFRP干涉螺接构件为研究对象，开展冲击载荷下拉剪损伤演变机理研究：发展脉冲电磁力加载的拉剪冲击力学性能实验方法，揭示构件物理损伤特征及积累演变机理，理解宏观力学响应的微观物理损伤影响机制；结合理论探索，建立考虑应变率和惯性效应的损伤预测模型，分析加载速率和干涉量耦合作用下的应力场分布及变化规律，掌握应力场对损伤行为的影响关系，探索冲击损伤的干涉连接影响规律及作用机制；基于研究结果，提出构件抗冲击损伤性能强化策略，为飞机复合材料结构抗冲击损伤性能评估和优化提供可靠的理论支持和方法。

轻量化是飞机尤其是大型飞机研制的重要主题，为此碳纤维增强复合材料（CFRP）被广泛应用。螺接是CFRP结构最主要的连接方式，但CFRP抗冲击性能差、易损伤，其螺接构件冲击损伤是飞机结构可靠性提升的瓶颈。干涉连接能显著提高CFRP螺接构件疲劳寿命和静强度，但对冲击损伤行为的抑制机理尚待研究。为此，本项目以CFRP干涉螺接构件为研究对象，开展冲击载荷下拉剪损伤演变机理研究。首先，发明了基于脉冲电磁力加载的构件冲击力学性能测试方法和装置，建立了脉冲电磁力与关键放电参数的映射关系，提高了冲击加载的加载精确度和可控性。随后，开展了构件冲击力学性能测试，发现层板冲击失效过程表现出明显的局部碎化特征，其破坏主要由局部高水平冲击应力引起，钛合金连接孔和螺栓冲击变形程度低于准静态加载。干涉配合通过改善螺栓与连接孔的实际接触状态，进而优化了试件实际局部冲击应力承载分配和分布特征，具有明显的抑制冲击损伤的产生和提高挤压强度的效果，并与冲击速度一起对试件最终失效模式产生影响。然而，干涉配合对构件冲击失效强度改善不明显。最后，建立了构件渐进损伤力学模型，有限元建模研究发现干涉配合对提高接头刚度具有较大影响，但随着干涉量的增加影响的边际效用下降。干涉配合通过降低构件局部应力集中，对裂纹萌生和扩展具有抑制作用。然而，干涉配合本身在孔周引入了残余应力，干涉量过大反而对裂纹萌生和扩展具有促进作用。因此，0.4%及以下的小干涉配合可以更好利用裂纹抑制作用，同时尽量规避了大干涉配合的裂纹促进作用。本项目研究结果可为飞机复合材料结构抗冲击损伤性能评估和优化提供理论支持和方法。