To achieve optimal adhesive strength for applications that involve bonding dissimilar substrates, many factors must be considered. Some include service conditions, joint design, curing, thermal, electrical and mechanical properties, and more. When bonding substrates with widely different thermal expansion coefficients (CTE) it is essential to consider these issues before choosing an adhesive system, to ensure that specific requirements are met.
Commonly Bonded Dissimilar Substrates
Adhesive Systems for Dissimilar Substrates
To enhance resistance to thermal cycling, shock and vibration, it would be best to choose an adhesive that exhibits a “give” or flow upon pressure applications. This will also minimize the potential of failure from fatigue or hysteresis due to the forces generated in the joint. These cases require specially formulated compositions so that the adhesive produces a toughened, rather than an entirely anodized bond.
Toughened two part systems comprise a major amount of a traditional high strength rigid epoxy and a smaller amount of an elastomer modified epoxy. This combination is designed to accommodate thermal and/or mechanical shock and vibration induced stresses which would negatively impair the rigid phase.
There is another approach when there is a wide difference between the CTEs. One can consider more flexible compounds via the incorporation of flexible epoxies, blocked urethanes or polysulfide type polymers. These systems typically have higher peel strength and lower shear strength.