具芳纶短纤维增韧界面的碳纤维夹芯结构性能、机理和分析

碳纤维夹芯结构常用作航空航天、交通车辆等运载工具的主承力结构,这类结构在服役过程中容易发生界面开裂,继而引发大面积脱粘、面板局部屈曲等破坏模式,严重影响结构的安全.使用芳纶短纤维对碳纤维夹芯结构的面-芯界面进行增韧,在夹芯结构制备过程中,在界面加入低密度芳纶短纤维薄膜,通过芳纶短纤维的桥联作用,提高界面的粘接性能.首先通过弯曲和压缩实验,对比了增韧和未增韧夹芯结构的荷载-位移曲线、破坏模式等响应,发现芳纶短纤维界面增韧可以大幅提高碳纤维夹芯结构的各项力学性能.其次,基于非对称双悬臂梁实验和扫描电镜观测,分析了芳纶短纤维的增韧效果和增韧机理.最后,基于均匀弹性材料裂纹的奇异性解和界面裂纹尖端的位移震荡解,建立了考虑界面裂纹尖端复杂应力场的扩展有限元单元,模拟了碳纤维夹芯试件的界面开裂过程.以上研究工作有助于揭示芳纶短纤维增韧界面的断裂机理,建立界面增韧参数设计方法,提高碳纤维夹芯结构的力学性能,并为结构的健康诊断和工艺改进提供科学依据.

Properties, mechanisms and their analysis of carbon fiber sandwich structures with short-aramid-fiber interfacial toughening

Carbon fiber sandwich structures are widely used as load-bearing structures in aerospace, automobile and other vehicles. Interfacial fracture, which frequently occurs in these structures, could lead to large-area debonding, face-sheet buckling and significantly affect the structural safety. Short-aramid-fibers were selected to toughen the interface of carbon fiber sandwich. Low density tissue of short-aramid-fibers were inserted at the interface during the manufacturing of sandwich structures, and the interfacial toughness was enhanced by bridging effect of short-aramid-fibers. The load-displacement curves and failure modes of toughened and plain sandwich specimens were firstly compared through bending tests and compressive tests. The experimental results indicate that various mechanical properties are all reinforced by short-aramid-fiber toughening. Then, the toughening effect and mechanism of interleaved aramid fibers were examined by asymmetric double cantilever beam test and scanning electron microscopy respectively. Finally, based on the singularity solution of uniform elastic material crack and displacement shock solution of crack tip of interface, an extended finite element model (XFEM), which considered the complex stress field at the crack tip of interface, was proposed for simulation of interfacial fracture of carbon fiber sandwich structures. This study will benefit the disclosing of fracture mechanism of short-aramid-fiber toughened interface, establishing the method of designing interfacial toughening parameters, increasing the mechanical properties of carbon fiber sandwich structures, and providing scientific basis for health monitoring and manufacturing of this kind of structure.