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

© 2016, Editorial Office of Journal of Dalian University of Technology. All right reserved. 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.