Delamination is a failure mode in which a material fractures into layers. A variety of materials, including laminated composites[1]​and concrete, can fail by delamination. Processing can create layers in materials such as rolled steel[2]​[3]​ and plastics and metals "Metal (material)") from 3D printing[4]​[5]​ that can fail due to separation of their layers. Additionally, surface coatings such as paints and films can delaminate from the coated substrate.

In laminated composites, the adhesion between the layers usually fails first, causing the layers to separate.[6]​ For example, in the case of fiber-reinforced plastics, high-strength reinforcing sheets (such as carbon fiber or glass fiber) are bonded together using 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 detach from the polymer.

Delamination also occurs in reinforced concrete when metal reinforcements near the surface corrode.[7] The oxidized metal has a greater volume causing stresses when confined by the concrete. When those stresses exceed the strength of the concrete, cracks can form that extend to join neighboring cracks caused by corroded rebar, creating a fracture plane that runs parallel to the surface. Once the fracture plane has developed, the concrete on the surface can separate from the substrate.

Processing can create layers in materials that can fail by delamination. On concrete, surfaces can peel off due to inadequate finishing. If the surface is finished and densified by troweling while the underlying concrete is shedding water and air, the dense top layer can separate from the water and air by pushing in an upward direction.[8]​ In steels, lamination can create a microstructure when microscopic grains orient into flat sheets that can fracture into layers.[2]​ Additionally, certain 3D printing methods (e.g., fused deposition) build parts in layers that can delaminate. during the same printing or use. When printing thermoplastics with fused deposition, cooling a hot layer of plastic applied to a cold substrate layer can cause flexing due to differential thermal contraction and separation of the layers.[4]​.

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