多轴向经编织物及其涂层织物在有限变形下的本构建模及破坏机理研究

The Multi-axial Warp Knitted fabrics (MWK) have much higher initial stiffness than traditional woven fabrics due to the non-woven yarns and are usually used as reinforcements for composites. MWK coated fabrics have been widely applied to aerospace engineering, civil engineering and other industries. However accurate constitutive models for MWK fabrics with and without coating are not available in the literature because of the difficulties to model the materials’ deformation mechanisms such as the slippages between yarns in fabrics. In this proposed project, 2 sets of 2-camera Digital Image Correlation (DIC) system are utilized to measure the deformation and failure mechanisms at meso-scale (yarn scale) and macro scale simultaneously. The meso-scale unit cell models are then developed for the fabrics based on the experimental observations to capture the correct deformation mechanisms such as the slippages between yarns. The ultimate strength of the yarns obtained in the experiments is introduced to the meso-scale models to simulate the progressive failure of the fabrics. The meso-scale models can be validated by comparing their predictions with the experimental observations at both the meso scale and the macro scale. After that, the macro-scale constitutive models and failure criteria for the fabrics are derived from the meso-scale models based on the continuum mechanics. The research will not only promote the design optimization and applications of MWK fabrics in industry, but also pave the way for mechanical modeling of other types of fabrics.

多轴向经编织物因其纱线无卷曲而具有初始刚度高的优点，经常被用作复合材料的增强骨架，其涂层织物已广泛应用于航空航天、土木建筑等领域，但因难以描述其纱线之间的滑移等困难导致目前没有准确的相关本构模型。本项目计划使用两套双相机全场变形测量系统（数字图像相关（DIC）系统）同时定量观测织物在纱线层级介观结构变形和宏观变形与破坏，建立材料的单胞介观模型，充分考虑纱线之间的滑移等变形机理。在介观模型中引入试验所测得的纱线断裂强度，可模拟织物材料的逐步破坏，通过数值模拟把介观模型预测的结果和试验结果在介观和宏观两个尺度上相比较来验证模型。基于连续介质力学理论由单胞介观模型推导出织物及其涂层织物的宏观本构模型和破坏准则，为多轴向经编织物及其涂层织物的设计、制造和应用提供理论基础。这种试验、介观/宏观理论建模和数值模拟相结合的方法也可推广到其它类型织物的力学研究。

多轴向经编织物具有初始刚度高、可设计性和可加工性强等优点，被用作复合材料的增强骨架，同时由于其涂层织物具良好的延展性，已被广泛应用于工程领域。但由于其结构和变形的复杂性以及几何和材料的非线性，导致目前仍然难以准确预测多轴向经编织物及其涂层织物的宏观力学性能。同时，由于在实际应用中其受载情况的多样性和复杂性，导致很难分析其受载过程的变形机理和破坏模式。本项目通过将单轴拉伸和双轴拉伸加载系统与数字图像相关（Digital Image Correlation, DIC）系统相结合，对多轴向经编织物及其涂层织物的变形过程进行了实验测试研究，总结分析了其变形机理和破坏模式。建立了多轴向涂层织物的单胞介观模型，在小变形下对其弹性参数进行了理论预测，对相应变形过程的变形机理进行了理论分析，并采用代表性体积单元（Representative Volume Element, RVE）进行了数值验证。在有限变形下，通过充分考虑纱线之间的滑移等变形机理，建立了多轴向经编织物桁架形式的介观模型，通过引入应力梯度概念，基于连续介质力学理论解释了滑移的产生机制。本项目的研究成果为多轴向经编织物及其涂层织物的设计、制造和应用提供理论基础。