冲击载荷下天然纤维增强复合材料非线性粘塑性本构特性及断裂机理研究

More and more natural fiber replacing man-made fiber reinforced polymer composites are widely used in much industrial engineering. The study on dynamic mechanical behaviors of natural fiber reinforced polymer (NFRP) composites should be further strengthen. This project will design the NFRP composite of high strength and good toughness at first. The novel experimental technology of static and Hopkinson tests will be developed to obtain accurate and effective stress-strain information at different strain rates and temperatures. Based on the above experimental results, the macro dynamic constitutive response of NFRP composites will be investigated. The fracture of recovered specimens are analyzed using XRD, SEM, optical microscope and so on, the damage evolution equation and critical damage degree of the material will be determined. Based on micro structure of NFRP composites and the mechanical properties of component materials, the micro mechanical model considering strain rate, temperature and damage evolution are presented for applying the model to composites by combining theory with experiments and simulation of impact tensile tests of NFRP composites specimens. The fracture information is obtained by different stress state spalling tests under high strain rates and impact tensile failure tests at different strain rates and stress triaxialities. The dynamic fracture mechanism of NFRP composite will be studied in combining micro observation of recovered testing specimens with above results. The failure laws of NFRP composites depending on strain rate, stress triaxiality and Lode parameters are revealed by theory, numerical simulation using macro and micro constitutive model and experiments.

越来越多天然纤维代替人工纤维增强高聚物复合材料在工业工程中广泛应用，天然纤维增强高聚物（NFRP）复合材料相关动态力学响应研究需要进一步加强。本项申请首先设计韧性好、强度高的NFRP复合材料，并发展准静态及动态试验新技术，获得不同应变率、温度下精确有效的应力-应变信息，研究NFRP复合材料的宏观动态本构响应。通过NFRP复合材料试验不同应变回收试件的微细观分析，建立损伤演化方程并确定损伤度准则。基于NFRP复合材料的微观结构及各组分材料的力学性质，探讨建立适用于复合材料计及应变率、温度及损伤演化的微力学模型。通过高应变率下不同应力状态的层裂试验及不同应变率、应力三轴性的冲击拉伸断裂试验，获得材料的断裂信息，结合回收试件的微观分析结果，研究NFRP复合材料的动态断裂机理，揭示NFRP复合材料的断裂对应变率、应力三轴性及罗德角的依赖性。

1）优化设计了韧性好、强度高的天然纤维增强高聚物复合材料：考虑天然纤维与热塑性基体材料的不相容且在基体材料分散不均等特征，在基体材料中加入用硅烷修饰后定量天然纤维加入少量的经修饰的纳米粘土颗粒，天然纤维更容易均匀分散在基体材料中，且天然纤维与基体材料的粘结力也显著增强。在填料中加入少量的长玻璃纤维热熔到基体材料中得到了强度较高、韧性更好的复合材料。.2）开拓了天然纤维增强复合材料的冲击载荷拉伸、压缩的试验新技术：使用特制夹具在Hopkinson拉杆试验装置上进行板条试件的冲击拉伸致断裂试验，基于高速摄影记录图片，使用数字图像相关技术精确确定试件的变形信息，为研究天然纤维增强高聚物复合材料动态力学性能提供可靠的实验数据。.3）构建并验证了不同天然纤维增强高聚物复合材料的动态本构方程：基于DIC精确获得的应力-应变曲线，构建计及应变、应变率的分离多项式动态本构方程，使用所构建的动态本构方程数值模拟NFRP复合材料在不同应变率下的拉伸试验，并与试验结果进行比较。.4）提出一种适宜于天然纤维增强复合材料的动态断裂判据：根据NF增强PP复合材料在不同应变率下的拉伸试验结果、高速摄影记录的图像及断口形貌特征，理论、试验相结合的方法，基于动态应变能密度，提出一种依赖于应变率的天然纤维增强高聚物复合材料的动态断裂判据。