Epoxy adhesives fracture mechanics

In a contribution from B. F. Goodrich, Drake and Siebert extensively review the journal and patent literature since 1975 on reactive butadiene/acrylonitrile liquid and solid elastomers used in formulating epoxy structural adhesives. Areas reviewed include the preparation of elastomer-modified epoxy resins, the characterization of rubber-toughened epoxy resins, fracture mechanics and adhesive formulation and testing. 

Fracture mechanics characterisation tests have been performed to determine the mixed mode fracture envelope of an epoxy bonded glass/epoxy composite. Analysis of lap shear, and L-stiffener geometries has shown that for this relatively brittle adhesive reasonable first estimations of failure loads can be obtained for both cracked and uncracked specimens. An image analysis technique has been developed which enables failure mechanisms to be... 

In contrast to polyethylene and EVAs, Epoxide adhesives are thermosets and are much stiffer and less ductile. The adhesion fracture energy (Gc, see Fracture mechanics), between both unmodified and rubber-toughened epoxies (see Toughened adhesives) and several metals has generally been found to be much higher when microfibrous surfaces were involved (Table 2) ... 

Some authors have refused to accept the role of interfacial adhesion on the toughening of thermoset resins. Lavita and co-workers [190] reported that non-reactive rubber can toughen BPA-modified epoxy, but the mechanism was not fully discussed. Huang and co-workers [194] showed that when the second phase consists of micron-size rubber particles, the interfacial bonding has only a modest effect on the fracture properties of blends. 

Of particular interest is whether there is a lower limit to the applied stress below which no environmental attack is observed and this has been investigated in some detail using a fracture mechanics approach [36,45,136,137]. The TDCB geometry (see Table 7.1), consisting of aluminium alloy beams bonded with an epoxy adhesive, has been widely employed and the commonly used experimental technique has been to place this specimen under an applied load in the environment of interest and monitor the rate and locus of crack growth. The typical observation is that the cohesive in adhesive starter crack does not... 

Ural A, Zehnder AT, Ingraffea AR (2003) Fracture mechanics approach to face sheet delamination in honeycomb measurement of energy release rate of the adhesive bond. Eng Fract Mech 70( 1 ) 93-103 Xiao GZ, Shanahan MER (1997) Water absorption and desorption in an epoxy resin with degradation. J Polym Sci B 35 2659... 

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. 

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