纤维金属层板铆接湿-热-力-微动耦合行为与疲劳寿命关系的研究

Fiber metal laminates (FMLs) can be machined and riveted like conventional metal mateirals. However, more complicated interface edges among metal layer,fiber layer and rivet exist in riveted joints of FMLs than in those of metal plates. Fretting wear exists between rivets and other materials, and between FMLs and frameworks,both bonded interface and fretting interface exist in these interface edge configerations, so that the mechanical behavior near the interface edges are difficult to predicted. Under coupled hydrothermal, mechanical and fretting contact loading, fatigue breakage is prone to happen at the interface edges because the material properties and geometries are discontinous. In this project, the complicated rivet joints of FMLs are taken as the study object. Firstly, hydrothermal-mechanical-fretting behavior of interface edge among metal, fiber reinforced composites and rivet materials are analyzed by fracture mechaics method, and a kind of super interface edge element is established based on local solutions of stress and displacement fields and the generalized variational principle; Secondly, the effects of hydrothermal- mechanical-fretting loading, geometry type, physical dimension, fit types and friction coefficients on strengthes of local stress and displacement fields are solved by the super interface edge element, and empirical equations of generalized stress intensity factors (GSIFs) versus these influence factors are predicted; Thirdly,The relational expressions between fatigue crack initiation life and GSIFs, and between early crack propagation ratio and GSIFs are established to predict the fatigue life of rivet joints in FMLs; Finally, physical dimensions, riveting types, materials properties and processing technic are optimized to improve local mechanical environment and fatigue resistance, and suggestions for long life rivet joint design are offered according to the optimization results.

纤维金属层板铆接孔和铆钉之间形成了比单一金属板铆接更复杂的界面端-金属层/纤维层/铆钉界面端。其中既存在接合界面、又存在微动界面，力学行为非常复杂。由于材料和几何不连续，在交变湿热效应、力(远场载荷、钉载和钉孔配合力)和微动接触共同作用下，界面端极易发生疲劳破坏。本项目以纤维金属层板铆接界面端为研究对象，在湿-热-力-微动接触耦合作用下，建立界面端邻域应力场强度力学分析模型，并基于变分原理建立杂交应力单元；确定湿-热-力-微动载荷、结构几何、钉孔配合和微动参数等影响因素对界面端局部力学行为的影响规律、适应范围和依赖关系；确定界面端广义应力强度参数，并建立其与各影响因素之间的经验关系式；结合试验，确定基于应力强度参数且适用于层板铆接界面端的疲劳裂纹萌生和早期扩展寿命预测模型；通过优化界面端干涉情况来，来约束界面端力学行为，提高微动疲劳抗力，为复杂服役环境中纤维金属层板铆接结构设计服务。

纤维金属层板铆接孔和铆钉之间形成了比单一金属板铆接更复杂的界面端-金属层/纤维层/铆钉界面端，层板极易发生损伤和疲劳。.本项目研究以下内容：.(1) 复合材料界面端应力场分析技术研究.分别建立了机械载荷下界面端奇异性应力场数值特征解求解模型、热-力载荷下界面端奇异性应力场数值特征解求解模型和三维圆柱界面端奇异性应力场特征解解析和数值求解模型。基于广义变分原理建立界面端超级奇异单元，与传统有限元单元模型组装，建立复合界面端耦合力学行为分析的高等有限元模型。.(2) 复合材料界面端应力场强度的研究.(a) 纤维夹杂界面端局部应力场强度研究.将复合材料纤维截面视为多边形夹杂，利用界面端高等有限元模型分析夹杂局部力学行为，求解夹杂角部广义应力场强度因子，并基于单胞模型研究复合材料中多夹杂干涉情况下的奇异性应力场强度问题，最终确定纤维增强复合材料夹杂/基体界面角部局部破坏影响因素。. (b) 纤维金属层板铆接损伤理论体系构建.建立了纤维金属层板铆接部位耦合损伤理论体系：采用Johnson-Cook失效准则预测金属层损伤、采用三维Hashin损伤准则预测复合材料层损伤、采用脱层失效理论预测层间开裂。通过损伤预测模型考察层板铆接部位损伤演化和刚度退化，为FMLs铆接设计提供可行性建议。.(c) 金属导线层弹性延展性研究.建立基于最大主应变和半宽度塑性容限强度准则，预测柔性基体上无屈曲互连导线层的延展性，并探索无屈曲互连高延展性设计。.(3) 纤维金属层板接触微动疲劳寿命预测技术的研究.基于应变能的多轴疲劳理论建立微动疲劳寿命控制参数求解理论体系，并建立广义疲劳强度参数变程与疲劳裂纹萌生寿命之间的关系，从而建立湿热-力-微动接触耦合情况下复合材料/铆钉材料界面端疲劳裂纹萌生寿命和扩展寿命预测模型。.(4) 纤维金属层板铆接微动疲劳寿命预测.以纤维金属层板铆接接触界面端为研究对象，根据应变能密度准则建立纤维金属层板铆接部位疲劳裂纹萌生寿命预测模型，通过实验验证了模型的有效性。