Delamination

A separation of the layers of a laminated material.
Delamination is a mode of failure for composite materials and steel. In laminated materials, repeated cyclic stresses, impact, and so on can cause layers to separate, forming a mica-like structure of separate layers, with significant loss of mechanical toughness.
Delamination of bonded composite materials causes the materials to lose strength.
to find the delamination on aircraft skins ,the technician should be use the tap test.