Graphite fiber composites fracture

Russell, A.J. and Street, K.N. (1987). The effect of matrix toughness on delamination static and fatigue fracture under mode I and II shear loading of graphite fiber composites. In Toughened Composites. ASTM STP 937 (N.J. Johnston ed.). ASTM, Philadelphia, PA, pp. 257-294. 

Finally, the basic Adhesive B formulation was toughened using the MEAc core-shell polymer and used as the matrix for an epoxy-graphite fiber composite. The mode II interlaminar fracture toughness, GIIc, was increased from 500 J/m2 to 890 J/m2 by the presence of the acrylic core-shell toughener. 

Figure 12.14. Fracture toughness of PPO composites, (a) PPO resin (b) 20% A-1100 glass-fiber composite (c) 20% glass-fiber composite (d) 20 % graphite-fiber composite (e) 20 % glass-bead composite (f) 20 % A-llOO glass-bead composite. The term A-llOO refers to the silane used as a coupling agent. (Trachte and DiBenedetto, 1971.)...

SEM analysis of both polished and fractured specimens. Applications of microscopy to the study of glass, carbon or graphite fiber composites will be explored, especially relating to the effects of processing, fiber length and interfacial bonding. 

Madhukar, M.S. and Drzal, L.T. (1992b). Fiber-matrix adhesion and its effect on composite mechanical properties IV. Mode 1 and Mode II fracture toughness of graphite/epoxy composites. J. Composite Mater. 26, 936-968. 

To detect EE from interply failure, the newly-formed fracture surfaces have to be exposed to the detector, requiring a change of sample and testing configuration. Such a study is currently underway, with unidirectional composites made from Hercules AU (untreated) and AS4 (surface treated) graphite fibers. 

Figure 12. EE from the interlaminar fracture of graphite/epoxy composites made with (a) untreated, and (b) surface treated fibers (Epon 828/mpda).

Conductive reinforcements in thermoplastics are a new application of composites [2891. High temperature resistant thermoplastics, such as PPS, PEI, PPO and liquid crystal polyesters, have been combined with conductive fibers, generally chopped graphite and nickel coated graphite. Fiber distribution, orientation and fracture morphology were determined by optical and SEM techniques. Poor bonding in the nickel coated graphite composite, as observed in SEM tensile fractures, resulted in lowered tensile and impact properties. 

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