Effect of heating on the structure of an adhesive joint, as indicated by electrical resistance measurement

Heating from 20degreesC to temperatures as low as 25degreesC was found to cause a partly reversible effect on the structure of an adhesive (epoxy) joint involving steel adjoining (bonded) components with a surface roughness of 120 mum, as shown by monitoring the contact electrical resistivity of the joint during heating and cooling. The reversible portion was due to thermal expansion of the adhesive. The irreversible portion was due to an irreversible microstructural change in the adhesive. These structural changes decreased the extent of electrical contact between the adjoining surfaces at asperities, thereby increasing the contact resistivity.