Debonding occurs when an adhesive stops sticking (adhering) to an adherend or substrate material. The adhesive does not have to be an organic, polymeric material; it could be an inorganic coating, for instance. Debonding occurs if the physical, chemical or mechanical forces that hold the bond together are broken, perhaps by a force or environmental attack.
Delamination is failure in a laminated material, often a composite, which leads to separation of the layers of reinforcement or plies. Delamination failure can be of several types, such as:
- fracture within the adhesive or resin
- fracture within the reinforcement
- debonding of the resin from the reinforcement
In this last instance, it is the debonding that leads to delamination, which helps to illustrate the distinction between debonding and delamination:
- debonding - when two materials stop adhering to each other
- delamination - when a laminated material becomes separated, perhaps induced by poor processing during production, impact in service, or some other means
The types of defect that occur in adhesive bonds are shown in the figure below, which shows debonding in the form of disbonds.
Here are some other common defects found in adhesively bonded joints:
- Porosity: caused by gases and volatiles in the adhesive.
- Voids: may be formed by coalescence of pores, but are more often caused by air entrapment during application of the adhesive, by volatiles or by insufficient adhesive being applied.
- Incorrect cure: may occur locally because of contaminants or poor mixing, but it is more likely to occur throughout the whole bondline, because of incorrect formulation or mixing, or thermal exposure.
- Cracks in adhesive: associated with curing and thermal shrinkage during manufacture, especially with some brittle, high temperature adhesives.
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