Local Surface Toughening – A boltless crack stopping technology for aerospace structures

Abstract

Bonding offers numerous advantages compared to bolted joints when connecting diverse materials. However, the drawbacks of a bonded joint can swiftly manifest under increased loads, a challenge notably prevalent in aviation. To address this issue, heavily stressed components in aviation utilize a hybrid approach, incorporating both rivets and adhesive for structural bonding. This strategy aims to accentuate the benefits of structural adhesive bonding while maintaining the safety associated with traditional bolted joints. Referred to as a fail-safe design, this concept prioritizes damage tolerance and enhanced resilience against manufacturing defects, achieved through a secure double load path. Especially when joining fiber-reinforced composites, bolts weaken the adherends of the joint and only contribute to load transfer when the brittle adhesive fails. Previous study investigates the impact of locally modified surface toughness on the structural adhesive bond under Mode I and Mode II loading conditions through quasi-static Double Cantilever Beam (DCB) and End Notched Flexure (ENF) tests. The results demonstrate a pronounced influence, indicating a substantial enhancement in bond robustness. In this study, a dynamic examination of local surface toughness modification using Cracked Lap (CLS) specimens reveals insights into the crack arresting capabilities. The results show that cracks can be stopped beyond the limit load of the laminate, proving the effectiveness of this technology as a crack stopper.