Disbondment

Disbondment refers to the separation of two materials that are bonded together by an adhesive or fusion joint, resulting in the loss of load transfer across the interface. It most often involves an interface between the adherend and the adhesive, but may also occur within the adhesive layer (cohesive failure) or in the substrate material (substrate failure). In engineering practice, disbondment is a common failure mode in bonded joints, laminates, coatings, and protective barriers, and is a major concern in aerospace, automotive, civil engineering, and electronics packaging.

Disbondment can occur via adhesive failure at the interface, cohesive failure within the adhesive, or substrate failure of the adherends. The relative occurrence depends on materials, surface preparation, curing, loading, and environmental conditions.

Causes of disbondment include surface contamination, moisture ingress, temperature cycling, chemical exposure, aging, UV exposure, poor surface preparation, incompatible adhesives and substrates, improper curing, residual stresses, impact, and geometric discontinuities. These factors can degrade adhesion or concentrate stresses at the bond line, initiating separation under service loads.

Detection and assessment rely on non-destructive testing and mechanical tests. Non-destructive methods include ultrasonic scanning, acoustic emission monitoring, infrared thermography, and X-ray or terahertz imaging; destructive tests such as lap shear or pull-off tests quantify bond strength and failure mode.

Prevention and remediation focus on sound process control and design practices: thorough surface cleaning and degreasing, surface activation or roughening, compatible primer and adhesive systems, proper curing, environmental controls, moisture barriers, and designs that minimize stress concentrations. When disbondment occurs, repair typically involves surface remediation, re-bonding, or replacement of the affected adherend.