• FastMat (ERC Consolidator Grant) - Coordinator: N. Ranc - Adminitrator: CNRS - 2017/2021.

Fast determination of fatigue behavior of materials beyond one billion cycle (FastMat)

Many mechanical structures are submitted to repeated loadings and can break under stress lower than the ultimate tensile stress.

This phenomenon is called fatigue of materials and can be found in many industrial sectors, such as the transport industry, aeronautic industry and energy production. Fatigue design is thus crucial in engineering and it requires the precise characterisation of material behavior under cyclic loadings to ensure the safety and reliability of structures throughout their life. An increase in the lifespan of a structure, or a reduction in the number of maintenance phases lead to increases in the number of cycles applied to this structure. It is presently common to find mechanical systems subjected to several billion cycles in what is called the gigacycle fatigue domain. The characterisation of the fatigue behavior of materials requires fatigue tests to be conducted until fracture for different stress amplitudes. One problem with this method is the test duration, which becomes excessive and beyond possible, particularly for a very high number of cycles. FastMat aims to develop a new method considerably reducing the duration of fatigue characterisation. This method involves the use of short interrupted tests coupled with a self-heating measurement to characterise the fatigue behavior for very low stress amplitudes. The scientific objective is to develop simultaneously experimental and numerical tools for the fast determination of fatigue behavior. The experimental approach will be developed to estimate simultaneously the dissipation and the stored energy, which directly reflect fatigue damage. For the numerical approach, discrete dislocation dynamics simulations will be developed to establish links between the fatigue damage associated with the evolution of dislocation structures, the stored energy and the dissipated energy.