Characterization of Fracture Properties of Nanographene Reinforced EPON 862 Polymer and Their Carbon Fiber Composites

Abstract

This paper describes the increase in Mode I fracture properties (stress intensity factor and energy release rate) of a thermosetting polymer EPON 862 and its nanographene reinforced counterpart. Low (0.1 and 0.5) weight percent nano-graphene platelets (NGP) were mechanically dispersed in EPON 862 and compact tension (CT) fracture experiments were conducted at quasi-static strain rates. Significant enhancement in fracture toughness (190%), and energy release rate (570%), was observed for nano-graphene reinforced matrix for only 0.5 wt% of graphene platelets. Fractography analysis of the fracture surface using SEM was performed to qualitatively visualize and understand the mechanism(s) responsible for the enhancement in these properties. Evidence of crack deflection (i.e., crack tilting and/or twisting) leading to increased surface roughness, graphene platelet pullout, and plastic deformation of the matrix caused by filler-matrix debonding corroborated by the presence of voids on the surface from SEM. AFM was employed to quantify the magnitude of surface roughness changes between the NGP reinforced and unreinforced fracture specimens, and correlate surface roughness changes to increased fracture toughness. Mode I Double Cantilever Beam (DCB) experiments were carried out to measure the delamination fracture toughness of carbon fiber reinforced laminates with NGP reinforced epoxy matrices. An enhancement of 42% in the fracture toughness was obtained for only 0.1 wt% NGP matrix laminates and a higher resistance behavior (Rcurve) to crack propagation was observed for the NGP matrix laminates in comparison to the baseline matrix counterparts.