Designing Adhesive Aging Studies

Aging of an adhesive bond

When designing aging studies of a bonded joint consider both the adhesive aging (cohesion) and the bond between both substrates (adhesion).  Several adhesive aging studies list the key factors are chemical, mechanical, physical effects, and time.

• Chemical effects on a bond joint can increase with concentration and temperature.
• Physical effects on a bond joint, like light and heat, can increase if mechanical and chemical factors are at play.  It is also significant to identify the speed at which the temperature changes and at what mechanical load the bond is under during that transition
• Mechanical effects like stress and load can differ with both chemical and physical effects.
• Time (or speed of change) can affect the bond more than it affects the adhesive.

For example, an adhesive bond that is exposed to an elevated temperature that is well within its service range may fail if it is cooled to the low end of the thermal range too quickly.  This is especially true when bonding dissimilar materials with different coefficients of thermal expansion.  The adhesive itself is designed to withstand the change, but the differential coefficients of thermal expansion are not always identified as a mechanical load.

Note that combinations of these effects can multiply the effects on the adhesive.

There are some instances where a product with a lower adhesive strength outperforms. Usually due to increased elongation and flexibility of the adhesive. This acts as a shock absorber during the thermal cycle.

ASTM has several standard methods for adhesive aging, which detail the test conditions and test procedures.