In this paper, the fatigue life and damage mechanism of plain weave composites under biaxial tension–torsion combined fatigue loading (TTF) are experimentally investigated. A biaxial TTF loading spectrum is designed to consider different fatigue frequencies and amplitudes, and an automated multi-module loading method with synchronized acquisition of the digital image correlation (DIC) and the testing machine is proposed. A comprehensive analysis of the experimental results, including fatigue lives, strain distribution, temperature variation, stiffness degradation, and typical damage morphologies at different fatigue cycles, has been conducted by utilizing DIC, infrared thermography (IRT) and computed tomography (CT). It is observed that the superimposed torsional fatigue load results in a rapid reduction in fatigue lives of plain weave composites, accompanied by more significant residual strain, energy dissipation, temperature rise and stiffness degradation. Particularly, the superimposed torsional fatigue loads mainly promote matrix cracking and debonding around the fiber/matrix interfaces, which then accelerates the damage initiations and accumulations of fiber yarns, ultimately leading to a rapid reduction in TTF fatigue lives. This study can provide valuable references for the design and safe application of plain weave composites under TTF loading.

中文翻译：

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双轴拉扭联合疲劳载荷下平纹复合材料疲劳寿命及损伤机制实验研究


本文对平纹组织复合材料在双轴拉扭联合疲劳载荷（TTF）下的疲劳寿命和损伤机制进行了实验研究。设计了双轴TTF加载谱以考虑不同的疲劳频率和振幅，并提出了一种同步采集数字图像相关（DIC）和试验机的自动化多模块加载方法。利用DIC、红外热成像（IRT）和计算机断层扫描（CT）对实验结果进行了综合分析，包括不同疲劳循环下的疲劳寿命、应变分布、温度变化、刚度退化和典型损伤形貌。研究发现，叠加的扭转疲劳载荷导致平纹复合材料的疲劳寿命迅速缩短，并伴随着更显着的残余应变、能量耗散、温升和刚度下降。特别是，叠加的扭转疲劳载荷主要促进纤维/基体界面周围的基体开裂和脱粘，从而加速纤维纱线的损伤萌生和累积，最终导致TTF疲劳寿命迅速缩短。该研究可为TTF载荷下平纹复合材料的设计和安全应用提供有价值的参考。