The interaction between corrosion management and structural integrity of aging aircraft

Abstract

A B S T R A C T Aircraft joints feature prominently in aircraft structural degradation; fatigue cracking and corrosion damage are major issues, which can reduce joint strength and degrade service life. Protecting the structure against corrosion usually involves use of highly developed protective coatings -paints and sealants -and, increasingly, the application of corrosion inhibiting compounds (CICs) which retard corrosion principally by penetrating into crevices and cracks, and displacing water. A combination of coatings and CIC use can provide effective corrosion protection, but both interact -in different ways -with joint structural performance and overall system durability. This paper discusses the interaction between these two corrosion protection measures and fatigue performance of joints. The first issue relates to the extent to which application of CICs (or other lubricants) can cause a reduction in the fatigue life of mechanically fastened joints. The CICs are lubricants which will reduce the friction at the faying surface of the joint, and change the load transfer characteristics of the joint. This paper discusses results from a test program assessing the fatigue life and failure mode of simple riveted lap joints; the results show a distinct reduction in fatigue life for joints containing CICs, and the paper discusses the changes thought to be responsible for the reduction. The second issue discussed is the degradation of protective coatings in service. Joints are key locations for coating cracking and failure, because areas such as sheet ends and fastener heads, where displacements are concentrated, may produce concentrated strain in coatings. So far, however, the potential influence of aircraft loading on coating degradation prognostics has received little attention. This paper discusses the role of joint displacement in service as a factor contributing to degradation in aircraft coatings at joints, and argues that this local strain effect, and indeed structural loading history, needs to be considered in predicting and assessing rates of coating degradation. It describes analyses of displacements in aircraft joints, to identify the levels of strain and to identify the roles and relative contributions of the various deflections in the joints. The results indicate the potential for very large strains in coatings.

Cellular Automata Modeling as a Tool in Corrosion Management

“…To effectively manage corrosion, a comprehensive understanding of the corrosion mechanisms associated with the Hydrogen Evolution Reaction (HER), Oxygen Reduction Reaction (ORR), and Oxygen Evolution Reaction (OER) is crucial, along with a deep knowledge of the operating environment and the factors that can either accelerate or mitigate corrosion. Additionally, it is essential to consider the applicable regulations and safety standards from NACE [8] or another standard that can apply regarding corrosion prevention across various industrial sectors, including petrochemicals [9], aeronautics [10], shipbuilding and maritime infrastructure [11][12][13][14], energy [15], mining [16], nuclear waste [17], microbial induced corrosion (MIC) [18], and atmospheric corrosion [19], among others. By incorporating this knowledge, industries can develop robust corrosion management strategies that ensure the safety, longevity, and optimal performance of their assets and infrastructure.…”

Application of augmented finite element and cohesive zone modelling to predict damage evolution in metal matrix composites and aircraft coatings

“…The first was to initiate from flaws generated by photo oxidation at the coating surface since the surface suffers from earlier degradation than the bulk (Skaja et al, 2006). This type also includes mechanical damage such as scratches, and repair or refinishing that can introduce non-uniform external surface features which can act as crack initiation points (Jaya et al, 2012). The second possible crack initiation sites were at high strain locations inside the coating, which mostly occur at interfaces between matrix and filler particles.…”

Corrosion Sensor Development for Condition-Based Maintenance of Aircraft

“…Employing (5) and (6), the dissolution of Al with water results in the formation of aluminium-hydroxide (Al(OH) 3 ) and the release of H 2 and is given by [8,14,15]:…”

“…For aircraft, the effects of corrosion damage are cumulative and can increase in severity if the damage is not detected early. A serious result of undetected corrosion is that it can have a cascading effect by which it can precipitate and accelerate fatigue damage [5] leading to a corresponding decrease in the load bearing capacity for that structure. In this respect, the structural integrity of the aircraft is undermined by two separate yet complicit factors.…”