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Load History Dependence of Fracture in Rubber-Toughened Epoxies



Donald L. Hunston, J He, R Raghavan, D Hoffman


It is well know that the most common toughening mechanisms in structural adhesives are viscoelastic processes so the fracture energies for bulk adhesive specimens and bonded joints vary with loading history. The work here examines this effect by measuring fracture energies for bulk specimens at a wide range of constant cross-head speeds and a series of more complex loading histories. The results for the constant cross-head speed experiments are consistent with previous studies in that decreasing the loading rate produced an increase in toughness. For most rates, the behavior was approximately linear elastic with little or no r-curve behavior. Below a critical rate, however, there was a transition to ductile failure with a very high fracture energy, a large r-curve, and significant permanent deformation that clearly violated the linear elastic approximation. With the more complex loading histories, the toughness increased with the time a sample was held at high loads prior to fracture. This was attributed to growth of the crack-tip deformation zone before the failure point was reached.
Adhesion Society


adhesion, adhesives, epoxy, fracture, r-curve, rheology, toughening, viscoelasticity


Hunston, D. , He, J. , Raghavan, R. and Hoffman, D. (2000), Load History Dependence of Fracture in Rubber-Toughened Epoxies, Adhesion Society, [online], (Accessed April 20, 2024)
Created December 31, 1999, Updated October 12, 2021