Elastic Limit of the Adhesive

The elastic limit can be established by using the thick adherend shear test to determine the stress/strain relationship. This test uses steel adherends which are so thick that under the test conditions, their distortion is small and the influence on the data is acceptably low. A typical curve is shown in Fig. 10. 

The area below the stress/strain curve within the elastic region is a measure of the ability of an adhesive to absorb energy. High energy absorption means that the likelihood of bond failure is reduced. 

Thick adherend shear strength test piece 

It is important to establish the elashc limit of an adhesive. When an assembly is required to function for many years, it is crihcal that the maximum stress experienced by the joint does not exceed this value. If the apphed stress is higher involving the plashc behaviour of the adhesive, a limited life only can be expected. 

The thick adherend shear test also provides data on the modulus of the adhesive. If we use this data along with a knowledge of the modulus and thermal expansion of the two materials being bonded together, it is possible to compute the stress levels experienced by a simple lap joint. 

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