Definition - What does Delamination mean?
Delamination is the loss of coating adhesion to a surface or between coating layers.
Delamination can occur in:
- Composite materials
- Reinforced concrete structures
- Laminated materials
Delamination tends to destroy a coating's strength and durability, as well as the material's aesthetic appearance.
Since uses of composite materials in aviation are increasing, delamination is increasingly an air safety concern, especially in the tail sections of the airplanes.
Concrete delamination is found most frequently in bridge decks and is caused by the corrosion of reinforcing steel or freezing and thawing.
Corrosionpedia explains Delamination
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 cause of delamination is weak bonding. Thus, delamination is an insidious kind of failure as it develops inside of the material, without being visible on the surface, much like metal fatigue.
Delamination failure may be detected in the material by its sound:
- Solid composite has a bright sound, while a delaminated part sounds dull
- Reinforced concrete sounds solid, whereas delaminated concrete will have a light drum-like sound when exposed to a dragged chain pulled across its surface
Other nondestructive testing methods used include:
- Optical time domain reflectometer testing
- Radiographic imaging
- Infrared imaging
When dealing with concrete delamination, it occurs when the fresh concrete surface is sealed or densified by troweling while the underlying concrete is still plastic and continues to bleed and/or to release air. The resulting delaminations are generally thicker than those caused by improper finishing. Delaminations are difficult to detect during finishing, but become evident after the concrete surface has set and dried.