Separation of layers in a composite or coated material along an internal interface, producing a loss of through-thickness mechanical continuity and integrity.

Principle

Interfacial adhesion and fracture mechanics govern whether an applied stress or environmental action produces separation along the interface: when the energy release rate or stress intensity at the interface exceeds its toughness, layers separate preferentially to bulk fracture.

Demonstration

A carbon-fiber/epoxy laminate subjected to low-velocity impact develops a region where plies separate internally (interlaminar cracks) visible by ultrasonic inspection but not by surface cracks; stiffness and compressive strength across the thickness are reduced.

Misapplication

Calling any surface crack or coating blister a delamination; assuming delamination always indicates poor adhesive chemistry rather than also resulting from impact, fatigue, or differential thermal expansion.

Consequence

Localized loss of load-carrying capacity, redistribution of stresses to adjacent plies, accelerated propagation under cyclic loading, and possible sudden catastrophic failure if critical area grows.

Reversal

Re-lamination or effective bonding that restores continuous load paths (e.g., through adhesive repair, resin injection, or thermal consolidation) reverses delamination by re-establishing interlaminar toughness.

Boundary

Applies to layered, laminated, or coated systems where discrete interfaces exist; excludes single-phase bulk cracks that propagate through a homogeneous material and surface corrosion not involving layer separation.

Semantic Tension

Often confused with adhesive failure (separation at the bond surface) and with matrix cracking; delamination specifically denotes separation between layers/plies rather than within a single material volume or strictly at an adhesive interface.

Synthesis

Delamination is the interfacial separation of layers in laminated or coated materials caused when interlaminar stresses, environmental attack, or damage overcome the interface toughness, producing internal cracks that reduce stiffness and strength and require targeted inspection and repair.