碳纤维三维编织复合材料损伤变形场及渐进破坏实验研究

As the main load-bearing structure in service, research on the real time characterization and failure mechanism of the dynamic damage evolution process of three-dimensional braided composites is great challenges. In present reseach, the method for full-field deformation measurement, acoustic emission (AE) dynamic signals acquisition and statistical description based on the damage status will be conducted by using digital image correlation method (DICM) and AE complementary technology. The behavior of damage evolution of carbon fiber three-dimensional braided composites is investigated systematically by experimental research and theoretical analysis. First of all, the braided composite specimens with different types are designed and produced. The experimental test systems for synchronous implementation of damage deformation measurement and AE monitoring are established. Secondly, the uniaxial tensile experiments of the composite specimens are performed. The relationship between the damage factor and AE characteristics is to be determined using AE signals and the real-time deformation fields. The effects such as braided method, braiding angle, fiber volume fraction and random pore defects on the progressive failure of the composites will be analyzed. The correlation and phase of the multi-scale evolution and the physical mechanism of the damage state probability entropy evolution of the composites will be clarified. In the end, with the help of composite material damage mechanics theory, the failure criterion based on the characteristics of AE signals and damage deformation fields during failure process of carbon fiber three-dimensional braided composites is proposed, and the failure mechanism of the composites is revealed. The results lay the foundation for the nondestructive evaluation and damage prediction of three-dimensional braided composite structures.

三维编织复合材料损伤破坏动态演化过程的实时表征及机理研究是其作为主承力结构服役面临的挑战性课题。本项目结合数字图像相关方法和声发射互补技术，采用全场变形测量、声发射信号动态获取和基于损伤状态统计描述的方法，对碳纤维三维编织复合材料损伤演化行为进行系统地实验研究与理论分析。首先，设计并制备不同类型编织复合材料试件，建立同步实现损伤变形测量和声发射监测的实验测试系统。其次，对复合材料试件进行单向拉伸实验，通过声发射信号与实时变形场信息，提取损伤因子与声发射特征之间的关系，分析编织方式、编织角、纤维体积分数和随机孔隙缺陷等对复合材料渐进破坏的作用规律，阐明复合材料多尺度演化的相关性、阶段性及损伤状态概率熵演化的物理机制。最后，借助复合材料损伤力学理论，建立基于破坏过程声发射信号和损伤变形场特征的碳纤维三维编织复合材料失效判据，揭示其破坏的机理。为三维编织复合材料结构的无损评价和损伤预报奠定基础。

三维编织复合材料损伤破坏动态演化过程的实时表征及机理研究是其作为主承力结构服役面临的挑战性课题。本项目结合数字图像相关方法和声发射互补技术，采用全场变形测量、声发射信号动态获取和基于损伤状态统计描述的方法，对碳纤维三维编织复合材料损伤演化行为进行系统地实验研究与理论分析。首先，设计并制备了不同类型编织复合材料试件，建立同步实现变形测量和声发射监测的实验测试系统。其次，对复合材料试件进行单向加载实验，通过声发射信号的特征参数分析、聚类分析和统计分析结果与实时变形场信息，提取损伤因子与声发射特征之间的关系，分析编织方式、编织角、纤维体积分数和随机孔隙缺陷等对复合材料渐进破坏的作用规律，阐明复合材料多尺度演化的相关性、阶段性及损伤状态概率熵演化的物理机制。最后，借助复合材料损伤力学理论，建立基于破坏过程声发射信号和损伤变形场特征的碳纤维三维编织复合材料失效判据，揭示其破坏的机理。哨兵函数曲线上S2部分中的突然下降，表明复合材料失去储存应变能的能力。三维四向编织复合材料拉伸过程高应变区域沿纱线的横向和纵向发展，最终形成以编织纱线为受载主体的锯齿状应变集中带。三维五向编织复合材料引入轴向增强纱线，在损伤过程产生更多的声发射撞击，出现更明显的纤维损伤。随着三维五向编织复合材料纤维体积分数的增加，基体开裂和纤维断裂对应的声发射信号数量增加。三维五向编织复合材料的编织角从30°降至20°时，损伤过程产生更多的高频声发射信号。复合材料拉伸损伤声发射信号统计分析实现了复合材料损伤演化谱空间和概率空间的动态多尺度描述。为三维编织复合材料结构的无损评价和损伤预报奠定基础。