étude des chargements thermomécaniques induits par le resserrement du trou en perçage du Ti6Al4V sous assistance cryogénique

Abstract : On account of the major economic and ecological stakes to which the aeronautic industry stakeholders had to react during the last decades, the composite mass percentage in aircrafts never stopped to increase and reached more than 50% in 2013 for the Airbus A350. Indeed, the aim always being to build lighter aircrafts, aluminum alloys (which represented more than 75% of the total mass in the 70’) were gradually replaced by other materials which were considered to have more advantageous mechanical properties to weight ratios and especially by CFRP (Carbon Fiber Reinforced Plastic). Since the CFRP/titanium alloy pair demonstrates a better thermal and electrochemical compatibility compared to the CFRP/aluminum alloy pair, the use of titanium alloys in aircraft increased as well.Therefore, many assembly cases are currently CFRP/Ti6Al4V hybrid stacks for which the goal is to be able to drill them in one shot, just as it was done for metal/metal stacks. Studies were carried out concerning hybrid stacks drilling and highlighted that the elevated temperatures during the Ti6Al4V drilling were mainly responsible for the non-fulfilment of aeronautical specifications. Based on these observations, the idea of using the cryogenic assistance emerged: cooling down the cutting area by using liquid nitrogen instead of classic modes of lubrication and cooling.Indeed, the latent heat that liquid nitrogen absorbs when it vaporizes makes it an excellent candidate to efficiently cool the cutting zone. Moreover, since it evaporates quickly at room temperature, it eliminates the need to clean the parts and to recycle the fluids while being neutral for the planet and the machine operator.This Ph.D thesis revolves around the study of cryogenic assistance effects in Ti6Al4V drilling and focuses especially on its impact on hole shrinkage. Indeed, the shape and dimensions of the drilled hole, as well as the thermomechanical loads induced by the operation depend on this little-known phenomenon. Therefore, this thesis proposes to highlight the key role of hole shrinkage in Ti6Al4V drilling and to give elements of analysis and understanding on the phenomenon, for dry and cryogenic cutting conditions.
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Johan Merzouki. étude des chargements thermomécaniques induits par le resserrement du trou en perçage du Ti6Al4V sous assistance cryogénique. Génie mécanique [physics.class-ph]. Ecole nationale supérieure d'arts et métiers - ENSAM, 2018. Français. ⟨NNT : 2018ENAM0025⟩. ⟨tel-01874808⟩

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