Fatigue damage and life evaluation of thick bi‐material double strap joints for use in marine applications

The present‐day interest in the use of composite‐steel joints in primary marine structures requires an in‐depth knowledge of the fatigue performance of thick adhesive joints. This paper reports on experimental tests performed on compliant (i.e., thick and ductile) adhesive joints based on a two‐component methyl‐methacrylate adhesive in unaged and aged conditions. Bi‐material double strap joint with thick adhesive bondlines is subjected to quasi‐static and fatigue loading, during which the specimens are monitored by digital mage correlation and infrared thermography techniques to evaluate the types and extent of damage that occur in the joint during fatigue loading. The S‐N curve of the aged joint is evaluated along with its fatigue limit. It is found that the unaged specimens fail due to cohesive damage, hackles, and disbond at the adhesive‐adherend interface and the aged specimens fail due to delamination within the composite. The specimens that survived fatigue loading showed similar residual strength as specimens that were not fatigue loaded.