Research at ANSTO into innovative technologies for the repair and maintenance of military aircraft will have implications on the service life of commercial and passenger aircraft, Brendan Fitzpatrick reports.
Over 4.3 million passengers will fly this year and every day about 104,000 flights bring people and goods to their destination. The global economy relies heavily on aviation with $17.5 billion of goods travelling by air every day representing 35% of global trade by value.
Fatigue and corrosion damage to aircraft structural components are a major threat to the safety and airworthiness of civil and military aircraft, particularly those pushed past their intended service life.
Dr Anna Paradowska, Senior Research Scientist and Industrial Liaison Manager at ANSTO, worked with a team led by DST Group’s Dr Wyman Zhuang to test different technologies used to repair damaged aircraft structural components.
“Structural integrity requirements for aircraft parts are of the highest level. The repaired components need to demonstrate that the restored component shall have a structural strength condition, equivalent or better than its original configuration,” says Zhuang.
Zhuang’s team applied advanced repair techniques to aluminium alloy 7075–T651 — a lightweight, high-strength metal used in the aeronautical industry since 1943.
DST Group used laser cladding to deposit aluminium-silicon powders onto damaged surfaces of 7075 plates. They then applied post-heat treatment to reduce detrimental residual stresses, making the alloy stronger.
Following these processes, the team applied Deep Surface Rolling (DSR) — a surface enhancement technique that can introduce beneficial compressive residual stresses and enhance fatigue performance of repaired components.
After the treatment, Paradowska and the team at ANSTO used a sophisticated neutron diffraction instrument, the strain scanner KOWARI, to compare measurements of 3-D residual stresses on samples treated with different repair methods.
“We used this instrument because it can provide sub-surface information about residual stresses non-destructively with high resolution measurements. Often this information can’t be obtained by other techniques.
Neutrons can penetrate deep into materials to acquire data about localised stresses in the deformed material,” says Paradowska.
“This powerful tool gives researchers a unique capability to study the same specimens going through various stages of manufacturing process.” The neutron diffraction measurements showed that DSR caused deeper and higher magnitude compressive residual stresses at the surface and into the substrate. These stresses increased both the yield and ultimate strength of the tested plates.
Fatigue tests confirmed that DSR increased the average fatigue life by over 500% compared to plates that were only laser-clad, while the post-heat treatment increased fatigue life by 40%.
While research is currently focussed on military applications, it will have ongoing implications to aircraft service life in the broader aviation industry.