Fatigue failure is a major damage mechanism of structural components and is a global issue with economic and societal impact. Fatigue life prediction in the design stage of the structural components, as well as the identification respectively the follow-up of this process from the early stages represent preventive actions against catastrophic failures in operation. With all the advanced level of scientific research and technological development, accidents continue to occur due to different causes (aging of structures, manufacturing processes, increasing loads and optimisation, new materials, etc.). Even some do not cause human loss, they produce very large material damage. In 2018, a woman died after being partially sucked out of a plane through a window broken by a bladder detached from the engine after a fatigue failure, [1]. The early cracking of blades in Trent 1000 aircraft engine produced by Rolls Royce caused a loss of £450m in one single year, [2]. The examples can continue and even some incidents are not publicized. All of these supports the idea that efforts to predict and analyse fatigue damage must continue in close cooperation between the research environment and industry.
Fatigue damage occurs in three stages: crack initiation, growth from small to short and long crack and final fracture of the component. The first two stages, which cover most of the fatigue life, are dominated by the interaction with microstructural features of the material. Reference studies describe the physical mechanisms of fatigue crack initiation based on the persistent slip bands which are formed at grain level and cause an accumulation of plastic deformation. In most cases, the prediction models for fatigue crack initiation based on physical damage mechanisms have been developed and applied on simplified computational models incorporating several grains with well-defined crystallographic characteristics (called Representative Volume Elements – RVE) which are then subjected to simple loads.
A current problem for accurate prediction of fatigue damage of structural components is the implementation of physical damage mechanism-based models for a real loading case characterized by a multiaxial stress/strain state. This is the primary area of investigation for this project. On the other hand, the accumulation of plastic deformation occurs with the release of strain energy, that can be captured using the acoustic emission technique. In this context, the objectives of the action are summarized as follows: 1) Development of a novel concept for the evaluation and prediction of fatigue damage. Fundamentally the concept consists of correlating the real stress/strain state with the physical mechanisms of material degradation at mesoscopic level; 2) Link results of the concept with detected AE signatures during experimental validation testing; 3) Develop the researcher’s knowledge and ability so he is recognized as an established independent researcher whilst benefiting the Cardiff University knowledge of the AE techniques to industry and academia.
[1] https://www.theguardian.com/business/2018/apr/17/philadelphia-plane-emergency-southwest-landing-engine-explosion-latest ;
[2] https://www.theengineer.co.uk/rolls-royce-problems-trent-1000/ ;
