Given the capacity of modern aircraft to carry passengers and freight incredible distances across the globe, the question must be asked: what is being done to protect these valuable flying vehicles against external forces, pressures and impacts? Non-destructive testing in the aerospace industry is a familiar part of any project to an aeronautical engineer, but to everyday consumers it’s not a term that is bandied about very often. Non-destructive testing, or NDT, is a scientific method of testing materials, components or systems without causing damage. Eddy-current testing, magnetic-particle testing, liquid penetrant testing, radiographic testing, ultrasonic testing and visual testing are the six most-common types of NDT, and are used to ensure that the working parts of any machine are strong and flexible enough to withstand the forces that are at play during ignition, operation, shut-down and maintenance of a machine.
Within the aerospace industry, NDT testing is crucial to ensure that aircraft are able to withstand the drag on the fins from the inertia of the aeroplane, water particles forming on moving parts of machinery and the momentum of the plane as it touches down. Extraordinary circumstances such as gales that are present during stormy weather or avian wildlife becoming stuck in moving engine components must also be considered in terms of an aircraft’s capacity to carry on despite these environmental variables without becoming damaged or suffering a risk to its flight pattern.
Types of Testing
NDT testing relies on ultrasonic, electromagnetic, sound and other waves to test components for structural integrity, composition or condition. Imperfections in materials are detected by highly-sensitive components of testing equipment which detects stress on components caused by fatigue and general wear and tear. The methodology of ND testing is assured in its capacity to not impact the material being tested, and testing equipment is often supplemented with audio-visual equipment to provide observable indicators that a component is wearing out or that electromagnetic radiation or liquid is leaking. Indications that a component is undergoing stress are often invisible to the naked eye, so it’s necessary to conduct tests using enhanced sensory detection techniques to ensure problems that can escalate very rapidly later on are addressed before they get out of control.
In the context of aeronautical engineering, NDT is used throughout an aircraft’s life stages to ensure maximum safety standards are maintained at all times. From the qualification of new materials and the design of new engines to in-service aircraft inspections, NDT forms a crucial role at protecting aircraft from future damage to its systems and ensures it is up to standard national and international codes and regulation. NDT has been used historically to develop lightweight materials, flexible materials and durable materials which are all optimised for sustained aircraft flight in a safe manner.
A common application of NDT testing is to check components for cracks using fluorescent, highly viscous dye. Dye will be applied to an aeroplane component which is then cleaned, leaving residual dye to mark any imperfections in the surface of the component. This technique is optimised for sensitive surface parts that could be otherwise warped if placed under physical duress during testing. Sub-surface testing is usually done with radio waves, either ultrasound, x-rays or gamma rays depending on the thickness of the component. Similar to sonar waves, the radio waves detect defects in welds, fittings, joints, bolts and in adhesive bonds and identify which components need to be replaced during routine maintenance. Eddy Current testing is another subsurface NDT technique and is useful for determining where flaws in an aircraft are by analysing electromagnetic wave patterns. For detecting faults in liquids, bubble, pressure change, halogen diode and mass spectrometer testing techniques are used. These techniques involve immersing an object in pressurised liquid to detect leaks where gas bubbles are evident. Tests on magnetic materials are done using magnetic particle testing techniques: inducing a magnetic field in an object and then testing for imperfections using magnetic particles.
The Australian Institute for Non-Destructive Testing is the primary regulatory body who controls standards of non-destructive testing, promotes the use of NDT techniques and the NDT profession, facilitates the exchange of information between community members and acts as a certifying body in the qualification and later certification of NDT personnel.
The NDT industry is rapidly evolving along with developments in the technology used to carry out non-destructive tests. It’s assumed that the quality and durability of the aerospace industry will continue to improve along with increased NDT testing and the development of better NDT techniques. To carry out NDT, adherence to standards and training are necessary to ensure the high levels of efficacy continue in the aerospace sector. Check out our other post https://www.ndt.com.au/how-is-ndt-used-in-the-aerospace-industry/ for more information.