The cohesive mechanical properties of a toughened epoxy adhesive as a function of cure level

Stewart, I.J., Chambers, A.R. and Gordon, T. (2007) The cohesive mechanical properties of a toughened epoxy adhesive as a function of cure level. International Journal of Adhesion and Adhesives, 27 (4), 277-287. (doi:10.1016/j.ijadhadh.2006.05.003).

Abstract

The cohesive performance of an epoxy adhesive as a function of cure applied is evaluated through the use of mechanical testing, thermal analysis and electron microscope techniques. These materials characterisation techniques allow a complete analysis of the reference material in terms of mechanical behaviour, surface topography and thermally induced events during cure. The effect of cure level within the adhesive was explored by examining all the material properties as a function of post cure duration and temperature. Post cure temperature and duration were found to be directly proportional to the amount of curing reactions taking place within the system, with increases in post cure duration found to lower the temperatures required to cure to a specific level. The mechanical properties of the adhesive varied as a function of post cure harshness with a number of mechanisms conteributing to the strength during post cure. The elastic modulus of the material was found to decrease with increases in post cure temperature, more so than with increases in post cure duration. Large increases in ductility were witnessed at certain cure levels for each mode of loading. As curing levels are increased the glass transition temperature increases until a point where the energy required to cause the transition falls and the Tg is lowered. The morphology of the toughener has been characterised with spherical elements ranging from 0.06 -0.75micron, and inter- phase spacing also noted along with the distribution of elements. basic mechanical testsing of the adhesives were carried out in the form of lap shear and t-peel testing on mild steel substrates, the correlation with glass transition temperature being stronger in these modes.

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