Delamination

Delamination is a mode of failure in laminated materials in which two or more layers separate along an interface or within a layer. It is commonly discussed in fiber-reinforced polymers, where the layers correspond to plies of reinforcing fibers embedded in a matrix, but it can also occur in wood veneers, metal laminates, and multilayer coatings.

Delamination is typically driven by interlaminar stresses that exceed the adhesive or cohesive strength at an interface. Causes include manufacturing defects, moisture ingress, thermal cycling, impact loading, and long-term environmental exposure. Once a crack forms, it can propagate under service loads, reducing stiffness and carrying capacity and potentially leading to sudden failure.

In composites, delamination often starts at a void, resin-rich layer, or ply interface and can propagate under mode II or mixed-mode fracture. In wood products like plywood, delamination occurs along the glue line when joints fail due to moisture, heat, or adhesive degradation.

Detection methods include non-destructive testing such as ultrasonic C-scans, X-ray radiography, thermography, and acoustic emission; simple tap tests and visual inspection may indicate delamination. Destructive testing, such as peel or flexural tests, is used for material validation.

Prevention focuses on proper material selection, cure cycles, surface preparation, adhesive choice, moisture control, and design features that reduce interlaminar stresses, such as optimized ply stacking and scarf joints. Repair options include removing damaged layers and applying patches or replacing the laminate; bonding must restore interlaminar strength to recover structural integrity. Delamination remains a critical consideration in quality control and structural design across industries that rely on laminated materials.