Additive Manufacturing and Fatigue of cellular structures integrated in aerospace – FA2SCINAE

This objective will be addressed in the framework of a twofold approach, academic and industrial.
1) The academic approach aims at removing the locks associated with a better understanding of the fatigue mechanisms of lattice structures manufactured by EBM. Defects and their level of criticality will be identified first on the constitutive elements of the lattice structures, i.e. single beams of very small size (typically a few mm in diameter). In a second step, whole lattice structures will be studied. The effects of different types of post-treatments (mechanical, thermo-mechanical, or chemical) will be investigated.
2) Applications will be based on industrial case studies coming from two major end-users in the aeronautical field, namely Airbus SAS Operations and Zodiac Seats France. Structural parts will be (re)designed by integrating lattice parts. One will take into account of course the new requirements and design guide emerging from the academic studies. The new parts will be manufactured on an EBM machine from Poly-Shape company and tested on industrial benches.

Identification of the harmfulness of different types of defects: surface roughness, defects linked to the melting strategies, porosity, etc. This identification is performed in particular thanks to a systematic 3D characterization (X-ray tomography) before and after each fatigue test.
Application of three types of post-treatment: thermo-mechanical, chemical, and purely mechanical (shot blasting). These types of post-processing were first applied to single elements (beams of a few millimeters in diameter). The effects in terms of fatigue lifetime are quantified.

Studies at the scale of a whole lattice structure will follow the studies performed at the scale of a single beam.

Communications
1. « Study of the fatigue mechanisms of Ti-6Al-4V cellular structures manufactured by Electron Beam Melting », T. Persenot, J.Y. Buffière, R. Dendievel, E. Maire, G. Martin, J. Adrien, P. Emile, C. Archambeau-Mirguet, European Mechanics of Materials Conference (EMMC15), 7-9/09/2016, Bruxelles.
2. Fatigue mechanisms of Ti-6Al-4V cellular structures fabricated by Electron Beam Melting T. Persenot et P. Emile, Journées Annuelles SF2M 2016, 25-27//10/2016, Albi)

Additive manufacturing dedicated to metal parts is becoming more and more serious. Not only shapes are fabricated, but also mechanical properties begin to be now warranted. In the aeronautic field, fatigue, although one of the most important properties, is still rarely studied. The fatigue resistance is especially relevant for parts including very complex shapes such as lattice structures. This shape complexity is one of the strength of the additive manufacturing process.
In this context, project FA2SCINAE addresses some key points linked to the fatigue properties of parts integrating lattice structures and obtained by additive layer manufacturing. It focuses on a specific technology (Electron Beam Melting, EBM) and a specific material (titanium alloy TA6V, very useful in aeronautics). This project will mix an « academic approach » and an « applicative approach » of the problem.
Academic approach will concern the fatigue study of lattice structures as it. These structures will fabricated on the EBM machine in Grenoble INP (ARCAM A1 machine). They will be characterized microstructurally and mechanically (task 1). Fatigue mechanisms will be identified and some technical and scientific recommendations will be drawn. These recommendations will concern material characteristics such as relative density, strut size, microstructures, volume defects, surface irregularities, …. Post treatments will also be performed. They will concern either surface defects or metallurgical quality of the struts (task 2). Tasks 1 and 2 will be at the heart of a PhD thesis managed at INSA Lyon, in strong relationship with Grenoble INP.
Applicative approach will take place in a global context of design or re-design of aeronautic parts, in a weight saving perspective. Two case studies will be given by two end-users, Airbus and Zodiac, for structural parts submitted to cyclic loading. The first one corresponds to an outdoor part and the second one to an indoor part (cockpit seat). With an objective of weight saving, shape optimization approaches will lead to include lattice structures into the initial parts. Optimization constraints will have to take into account recommendations derived from task 1 and 2. ;
Polyshape company will manufacture the final parts with their EBM machine ARCAM Q20 (task 4). Post-treatments will follow. At the end, the final parts will be tested in industrial conditions by the respective end-users Airbus and Zodiac (task 5). TApplicative tasks 3 to 5 will be managed by two Post docs.
Finally, this project will lead to recommendations in terms of design, of useful lattice structures, of post-treatments efficiency, of qualifying procedures for EBM technology and TA6V material. It should give the aeronautical industry a proof of concept concerning the use of such lattice structures in respect with fatigue properties. It could also be useful for future normalization or certification procedures. Moreover, the concepts developed in the (re-)design step can be transferred to other technologies (e.g. laser) and other materials.