Fracture of Rubber-Toughened Adhesives: Viscoelastic Effects

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Abstract
In structural (or load bearing) applications of adhe sives, the system may be required to support loads over a wide range of temperatures for many years and thus even a small de pendence on temperature and rate (or time) can be very impor tant. For elastomer-toughened adhesives the high fracture energy is associated with a large crack-tip deformation zone and the optimum conditions are obtained when the bond thickness is approximately equal to the zone size. Increasing the loading rate or lowering the temperature shifts the optimum bond thickness to smaller values with little effect on the maximum fracture ener gy. Consequently, the fracture energy increases, decreases, or re mains relatively unchanged with increasing loading rate or de creasing temperature if the bond thickness is less than, greater than, or about equal to the optimum values, respectively. This result makes it possible to predict at least in a qualitative way the mode I failure properties of adhesive bonds as a function of load ing rate and temperature.