Delamination is a mode of failure where material fractures into layers.
A variety of materials including laminate composites and concrete can
fail by delamination. In laminated composites, the adhesion between layers often
fails first causing the layers to separate. For example, in fiber-reinforced
plastics, sheets of high strength reinforcement (e.g., carbon fiber, fiberglass)
are bound together by a much weaker polymer matrix (e.g., epoxy). In particular,
loads applied perpendicular to the high strength layers, and shear loads can
cause the polymer matrix to fracture or the fiber reinforcement to debond from the polymer.
Delamination also occurs in reinforced concrete when metal reinforcements
(i.e., rebar) near the surface corrode. The oxidized metal has a larger volume
causing stresses when confined by the concrete.
When the stresses exceed the strength of the concrete cracks can form and spread
to join with neighboring cracks caused by corroded rebar creating a fracture
plane that runs parallel to the surface. Once the fracture plane has developed,
the concrete at the surface can separate from the substrate.