ADHESIVE AND COMPOSITE BONDING
Some types of engineering components are often held together with chemical epoxy bonds. Examples are helicopter rotor blades (Aluminium bonded to Aluminium or stainless steel) or rubber covered steel rolls used in paper manufacturing processes and conveying equipment. (Rubber surface lining is bonded to steel roll)
From time to time these bonds fail. It is not always easy to determine whether or not they have failed due to excessive operating loads or because there have been deficiencies in manufacturing processes.
There are three different types of bond failures.
Cohesion (or ‘cohesive’) failure. The bond fractures through the adhesive.
Adhesion (or ‘adhesive’) failure. The bond fails along the interface between the adherends and the adhesive.
Mixed-mode failures. This is a mixture of cohesion and adhesion failures. It is often misinterpreted as a cohesion failure, is the most common and the most difficult to interpret.
Adhesion failures and mixed mode failures are contributed to by poor manufacturing processes particularly inadequate preparation of the bonding surfaces prior to bonding. If this occurs, the adhesive does not chemically bond properly to the adherends and over time this allows the adherend surfaces to react with water vapour in the atmosphere and hydrate, causing the bond to delaminate and fail.We at Prosolve are world leading experts in engineering bonding science and adhesive bonding failures. We have the expertise and experience to characterise and determine the type of bonding failures and the engineering factors that have caused them. Below are two case studies of different types of bond failures.
Case Study 1: This photograph montage shows a fragment of a helicopter rotor blade exhibiting adhesion and mixed mode bonding defects. These were caused by deficient manufacturing processes such as inadequate surface preparation of the bonded pieces.