三维编织复合材料局部变幅疲劳原位实验及失效机理研究

The three-dimensional (3D) braided resin-based composites have a wide application in aerospace and other fields, due to their excellent comprehensive mechanical properties. The 3D braided composites have defects such as cracks and delamination during the process of preparation, which causes the material stress concentration, and the initial damage will occur when subjected to the external loading. Together with the high degrees of heterogeneity and anisotropy of the 3D braided composites, the local stress will be redistributed. Even though the external loading has a constant amplitude, the material is locally subjected to variable amplitude loading, which makes the fatigue failure mechanism very complicated. Therefore, it is urgent to study the damage evolution and failure mechanism of the 3D braided composites under fatigue loading, and establish a reliable fatigue life prediction model. In this project, the in situ fatigue experiments of unidirectional composites and 3D braided composites are carried out, and the fatigue damage process and failure mechanism are revealed by Micro-CT scanning. Based on the 3D geometric reconstruction method, the 3D geometric model of 3D braided composites is established. Considering the local damage of the material, the Gauss point is subjected to the variable amplitude fatigue loading, and a fatigue elastic-plastic damage model of 3D braided composites is proposed. The fatigue life prediction method is built, and the key factors of the fatigue life of 3D braided composites are investigated. The study of this project will provide theoretical and technical support for fatigue design and evaluation of 3D braided composites.

三维编织树脂基复合材料综合力学性能优异，广泛应用于航空航天等领域。三维编织复合材料制备过程中存在裂纹、分层等缺陷，会出现应力集中，造成初始损伤，加上编织材料高度的非均匀性和各向异性，在外载荷下局部应力将重分布，即使外载荷是等幅疲劳载荷，材料在局部承受的也是变幅载荷，使得疲劳失效机理非常复杂。因此，迫切需要研究三维编织复合材料在疲劳载荷下的损伤演化与失效机理，建立可靠的疲劳寿命预测模型。本项目首先进行单向复合材料和三维编织复合材料的原位疲劳实验，利用微CT扫描揭示其疲劳损伤过程和失效机理。基于三维几何重构建模方法建立三维编织复合材料的精细化三维几何模型，考虑材料的局部损伤使得高斯点承受变幅疲劳载荷和基体的塑性，建立三维编织复合材料疲劳弹塑性损伤的细观模型，提出疲劳寿命预测方法，并研究影响三维编织复合材料疲劳寿命的关键因素，为三维编织复合材料的疲劳设计和评价提供理论和技术支撑。

三维编织复合材料具有高度的非均匀性和各向异性，在使用和服役过程中不可避免地承受循环交变载荷，失效机理非常复杂，发展三维编织复合材料力学性能的原位实验及渐进损伤分析方法，对推动其在航空航天领域的应用具有重要的理论意义和实用价值。本项目针对三维编织复合材料提出了一种基于Micro-CT的精细化建模方法，通过编写程序从连续CT切片图像中识别并提取纤维束截面轮廓，对截面轮廓进行空间重构自动生成了真实的编织复合材料细观三维几何模型。搭建了基于Micro-CT的原位力学性能测试平台，建立了编织复合材料及结构力学性能的原位在线检测技术和方法，通过三维图像重构技术实时监测了编织复合材料与结构在加载过程中微-细观结构的损伤演化过程，得到了结构的破坏模式，揭示了其复杂的失效机理。在细观尺度下考虑纤维束内纤维的断裂、纤维间的开裂和基体断裂等多种破坏模式，并考虑基体的塑性与损伤耦合效应，建立了三维编织复合材料的弹塑性损伤耦合分析模型，并提出了三维编织复合材料宏-细-微观层级传递的多尺度弹塑性损伤分析框架，发展了基于数据驱动的自洽聚类分析方法（SCA方法），实现了三维编织复合材料力学性能的高效预报。基于组分材料的剩余强度曲线，考虑组分材料不同的失效模式，建立了三维编织复合材料的疲劳失效准则，模拟了三维编织复合材料在循环载荷作用下的损伤演化过程，预测了三维编织复合材料的S-N曲线和循环加-卸载曲线，阐述了材料复杂的疲劳失效机理。在基金的支持下，在《Composites Science and Technology》、《Composite Structures》、《力学学报》、《航空学报》等期刊发表了学术论文18篇，多次参加国际、国内学术会议，并作分会场邀请报告，培养博士研究生3人（其中1人已毕业），培养硕士研究生3人（3人均已毕业）。

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