A Review of Corrosion in Aircraft Structures and Graphene-Based Sensors for Advanced Corrosion Monitoring

Abstract

Corrosion is an ever-present phenomena of material deterioration that affects all metal structures. Timely and accurate detection of corrosion is required for structural maintenance and effective management of structural components during their life cycle. The usage of aircraft materials has been primarily driven by the need for lighter, stronger, and more robust metal alloys, rather than mitigation of corrosion. As such, the overall cost of corrosion management and aircraft downtime remains high. To illustrate, $5.67 billion or 23.6% of total sustainment costs was spent on aircraft corrosion management, as well as 14.1% of total NAD for the US Air Force aviation and missiles in the fiscal year of 2018. The ability to detect and monitor corrosion will allow for a more efficient and cost-effective corrosion management strategy, and will therefore, minimize maintenance costs and downtime, and to avoid unexpected failure associated with corrosion. Conventional and commercial efforts in corrosion detection on aircrafts have focused on visual and other field detection approaches which are time- and usage-based rather than condition-based; they are also less effective in cases where the corroded area is inaccessible (e.g., fuel tank) or hidden (rivets). The ability to target and detect specific corrosion by-products associated with the metals/metal alloys (chloride ions, fluoride ions, iron oxides, aluminum chlorides etc.), corrosion environment (pH, wetness, temperature), along with conventional approaches for physical detection of corrosion can provide early corrosion detection as well as enhanced reliability of corrosion detection. The paper summarizes the state-of-art of corrosion sensing and measurement technologies for schedule-based inspection or continuous monitoring of physical, environmental and chemical presence associated with corrosion. The challenges are reviewed with regards to current gaps of corrosion detection and the complex task of corrosion management of an aircraft, with a focused overview of the corrosion factors and corrosion forms that are pertinent to the aviation industry. A comprehensive overview of thin film sensing techniques for corrosion detection and monitoring on aircrafts are being conducted. Particular attention is paid to innovative new materials, especially graphene-derived thin film sensors which rely on their ability to be configured as a conductor, semiconductor, or a functionally sensitive layer that responds to corrosion factors. Several thin film sensors have been detailed in this review as highly suited candidates for detecting corrosion through direct sensing of corrosion by-products in conjunction with the aforementioned physical and environmental corrosion parameters. The ability to print/pattern these thin film materials directly onto specific aircraft components, or deposit them onto rigid and flexible sensor surfaces and interfaces (fibre optics, microelectrode structures) makes them highly suited for corrosion monitoring applications.

Acoustic Emission Monitoring of Atmospheric Corrosion on Aluminum Aircraft Structures at Varying Relative Humidity

“…These can be exposed to various corrosive environments during operation. Common sources or corrosion promoting environments in the aircraft industries are aqueous electrolytes like sea spray in coastal regions or at flight over the ocean at low altitudes, system leaks of fluids as e.g., hydraulic oils or coolant fluids but also spillages inside the cabin like soups, coffee or mineral water can cause corrosion [1][2][3][4]. Furthermore, moisture from rain, fog or snow may form together with different pollutants like dirt, exhaust gases, sulfates, chlorides etc.…”

“…Furthermore, moisture from rain, fog or snow may form together with different pollutants like dirt, exhaust gases, sulfates, chlorides etc. electrically conductive and chemically reactive solutions that corrode aluminum [2]. If soluble salt contaminants are present and the relative humidity (RH) is above the deliquescence relative humidity (DRH) of the particular salt contamination, the salt takes up water from the ambient atmosphere and forms a highly concentrated electrolyte [5].…”

“…If soluble salt contaminants are present and the relative humidity (RH) is above the deliquescence relative humidity (DRH) of the particular salt contamination, the salt takes up water from the ambient atmosphere and forms a highly concentrated electrolyte [5]. Aircrafts operate in different climate zones and altitudes, hence they are exposed to fast changes in temperature and RH which can lead to condensation and in combination with salts or other contaminats to a corrosive solution [1][2][3]6]. Except to leakage and spillages of larger amounts of electrolytes, the above mentioned examples are typical sources of so-called atmospheric corrosion, which is the corrosion of a metal where the electrolyte is present in the form of a thin film, small droplets, or both [1,5,6].…”

A Hybrid Microfluidic Electronic Sensing Platform for Life Science Applications

“…A well-established member of electrochemical sensors, the so-called ion-sensitive field-effect transistor (ISFET) sensors have been utilized in different applications for ion/charge detection in chemical solutions. The ISFETs range from carbonaceous FET sensors (e.g., graphene, carbon nanotubes) to 2D materials (e.g., MoS 2 ) [ 7 , 8 , 9 , 10 ]. Many efforts have been made to develop ISFETs based on technologically flawless silicon-based complementary metal-oxide semiconductors (CMOS) technology, resulting in different sensing structures and topologies [ 4 ] offering high-yield productions.…”

Aircraft Fuselage Corrosion Detection Using Artificial Intelligence

“…Recently, Li et al [24] published a review of corrosion in aircraft structures for aviation monitoring. They collected data according to the flight path, time of the day, and month of the year.…”