Fatigue of metal materials and structures

Research on “Fatigue of metal materials and structures” studies the fatique damage to industrial parts in relation to the manufacturing processes and the environment they are used in.

This involves modeling the degradation phenomena observed in usage cycles of mechanical units or on sample tests on a relevant and validation of these models through experimentation. The structural applications also deal with design problems.

Three topics were developed.

Fatigue of structural bolted joints

This topic resulted from collaboration between the DGM of ENSICA and the LGMT of INSA through the thesis of Konan Koffi. The design and optimization of the aeronautical assemblies according to their static and fatigue resistance are the central focus of this research. Eric Paroissien’s thesis on the behavior of bonded-bolted hybrid joints is the continuation of this topic, both from a scientific point of view and through on-going collaboration with the LGMT.

This study made it possible to define the load transfer ratio of the adhesive and the bolts for an optimization of the number of bolts according to the adhesive’s properties.

The primary industrial partner is Airbus France, joined by other partners, including AXS, a software publisher and Aircelle, manufacturer of aircraft engine nacelles. AXS and Aircelle, along with the Trefle laboratory of ENSAM Bordeaux are our associates on the AXSPAD project, which has the Aerospace Valley seal of approval and is financed through FUI.

Fatigue and environment

This work focuses on thermomechanical fatigue, involving the use of an innovative thermal and mechanical fatigue test bench and associated numerical modeling. Since the first thesis, a certain number of actions (DEA studies and training courses) have contributed to the development of this test facility. Since then, current studies have turned towards the complex dimensioning of structures subjected to combined environments. Jihad Rishmany’s thesis illustrates this direction, with a focus on aeronautical heat exchangers and efforts to establish a relevant digital model capable of describing the mechanical behavior of the exchanger beam.

Fatigue and manufacturing processes

This research area is based on a study carried out in partnership with EDF concerning the relations between ranges of machining and resistance to fatigue of a structural steel. Machining can deteriorate the resistance to fatigue of the parts by modifying surface quality (roughness, residual stresses, microstructure).

The aim is to propose models in collaboration with the designer and the manufacturer to optimize the cost and the quality of their parts. A thesis carried out in partnership with Airbus France directly concerning the relations between surface quality/resistance to fatigue was completed in 2006 (Monchai Suraratchai). In relation to this work, another thesis was conducted, again in partnership with Airbus France and piloted by the “Advanced Numerical Methods” department, dealing with methods to predict the surface quality of a machined part based on cutting parameters. This thesis, defended by Jerome Limido in 2008, made it possible for the first time to our knowledge, to establish the pathway between, manufacturing parameters and part fatigue. This thesis proposes a sequence of models covering the range from cutting to fatigue behavior of an aluminum alloy through the description of the profile of the machined surface described by local Kt. Finally, a thesis explores the joint influence of machining and an anti-corrosion process on the fatigue resistance of an aeronautical aluminum alloy, in collaboration with Messier Bugatti and Airbus France. Research centers on surface mechanical properties. A thesis on the degradation of anodized surfaces of aluminum parts for spacecraft is being conducted by Yann Goueffon in partnership with CNES, ASTRIUM and CIRIMAT.