The objective of IDEFFAAR is to propose an engineering tool to asses the influence of casting defects on the fatigue behaviour of cast Aluminum alloys. The project is focussed on aeronautical applications but the active role of CTIF in the project allows extending the valorisation of results to other industries. The expertise and skills of the partners will support a quantitative evaluation of allowable casting defect in casting component production. Furthermore, fatigue tool proposed can be used to compute justification dispensation on a given component containing higher defect than expected. Industrial partners (MESSIER, HISPANO and AIRBUS) will have the opportunity to validate the tool on real components so that the methodology will result in a compromise between scientific advance and reasonable computational cost. IDEFFAAR aims to work on the following topics in order to overpass scientific issues on this topic. - Produce fatigue samples with representative defects (or bigger) in order to define allowable defect criterion. - Study 3D fatigue mechanisms from defects using high resolution X-ray Tomography. A special focus will be the competition between surface and internal defect regarding environmental effect. - Determine the role of environment on the fatigue behaviour in order to characterise the representative environment for an internal defect. - Define the equivalent defect size and morphology regarding fatigue. This definition should include relevant physical characteristics of the defects (morphology and microstructure) as well as constraints induced by the final implementation in an industrial FE code. - Propose a fatigue assessment methodology for structural components integrating directly the defect size. This methodology should be easy to use and time efficient. - Validate the Through Process Modelling proposed on industrial component (casting / NDT / fatigue) by the mean of fatigue tests performed on the structure. - Evaluation of the methodology in the case of temperature (150 °C) on fatigue samples. - Evaluation of the role of HIP and associated welding repair on the fatigue behaviour of fatigue samples. The whole project should allow doing scientific advances in fatigue mechanisms from defects and simulations while keeping a reasonable complexity in order to be used by fatigue design engineers.