An adhesive is a substance that fastens or bonds materials using surface attachment. The strength of an adhesive joint depends on the strength of the attachment of the adhesive to the material surface (substrate) termed adhesion and strength of the adhesive termed cohesion. Adhesives can also provide a sealing function.
There are many advantages in using adhesives compared to other fastening methods as listed below.
- Fatigue - There are few, if any, stress concentrations associated with adhesive joints
- Surface Area - For a lap joint the stress is distributed over a relatively large area. This provides a strong joint with lower specific stresses.
- An adhesive joint can provide a sealing function in addition to a fastening function.
- For a high production process an adhesive joint can be extremely economical.
- Compared to welding there are no high temperatures required.
- Adhesives are available for attaching a wide variety of different materials.
- Compared to bolted joints and rivetted joints there is less need for machined holes, and additional machined components.
- The is no weight penalty associated with adhesive joints.
- The stresses developed in an adhesive joint are almost entirely imposed by the operating conditions.
- For softer materials adhesives are the only real engineering option.
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Theoretically an adhesive joint is the ideal joint for permanently /semi-permanently fastening components together. Limitations of adhesive joints are listed below.- Certain adhesives are vulnerable to attack by chemicals /water.
- For the best joints surface preparation is important.
- Some adhesives require time to achieve design strength.
- An adhesive joint is intuitively not considered a sound joint.
- Many adhesives have a temperature limitation.
- For mass production, reliable joints jigs and fixture are important.
- Many adhesives are toxic and require care when being applied.
- Adhesive joints are often vulnerable to localised high stress due to peeling effect.
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