Researchers have worked with the University of Oxford and Rolls-Royce PLC to investigate cold dwell fatigue in engineering structures.

The findings have helped influence the safety assessments of both the European Union Aviation Safety Agency (EASA) and the USA Federal Aviation Administration (FAA).

Investigating dwell fatigue 

The research focused on dwell fatigue in titanium alloy components found in aero-engines. Dwell fatigue is the progressive degradation and cracking, which may develop during cyclic loading such as occurs during flight. Fatigue can compromise the safety of engineering structures; therefore, the researchers sought to understand the mechanistic basis of the fatigue cracking and to develop quantitative predictive models.

They used a range of techniques including transmission electron microscopy (TEM), high-resolution electron backscatter diffraction (HR-EBSD) and discrete dislocation plasticity (DDP) modelling to test how well the titanium alloys perform under various mechanical and thermal loads.

It was found that dwell fatigue occurs in particular microstructural features called macrozones which are strongly textured regions in titanium alloys. This revealed the importance of macrozones and time-dependent deformation (creep) in aero-engine compressors.

It also explained why dwell fatigue in aero-engine components depends on engine temperature, which varies greatly during flight.

Applications in the real world 

Along with the team's research in other journal articles, these findings were able to help resolve critical safety issues in the aero-industry.

The research explained the fatigue response observed in component tests in relation to in-service flight conditions, thereby contributing to safety certification by the aviation authorities.

Dr Yilun Xu co-authored the research with Dr Joesph Sudha, Professor David Dye, Professor Fionn Dunne, alongside researchers from Rolls-Royce PLC and the University of Oxford. Dr Xu commented that "this integrated research combines state-of-the-art experimental and modelling techniques. It has not only contributed to the materials science and engineering community by revealing the underpinning mechanisms but also benefits the lives of everyone by improving the safety of air travel."

Read the full article 'Predicting dwell fatigue life in titanium alloys using modelling and experiment' in Nature Communications.