Quantification of the pile-up effect for improving inverse mechanical analysis by means of nanoindentation

This paper deals with the identification of elastic-plastic material properties by means of nanoindentation. A dimensional analysis leads to the identification of a specific parameter based on the estimation of the pile-up effect. This parameter may be used in an inverse analysis. Theoretical aspects and experimental issues are discussed

Fretting wear_lubrication of initially worn parts through tribo-induced anchorage of PTFE in wear scars, and tribochemical creation of graphene oxide

International audienceFretting wear during launch operation is a well-known cause of anomalies in spacecraft. In this study, a CubSat satellite stayed stuck in its dispenser during the final preflight qualification test. So close to launch date, not a single part of the satellite could be replaced. A fretting test campaign has been carried out attribometer scale to propose a solution to lubricate the damaged contacts. In depth expertise of the satellite allowed to determine the contact parameters. Damages and particles observed on the rail surfaces were successfully reproduced. The tests showed the appearance of a continuous flow of loose particles that either leave the contact or agglomerate inside it. Those agglomerating induced high friction and high adhesion. After contact opening and cleaning off the particles, lubrication was applied on the resulting damaged surfaces. Sprayed alkyl-phosphonic acid molecules and grease containing PTFE were selected to be tested as lubricantbecause they could be applied manually. PTFE accumulated in the damaged regions, protecting the surfaces from further damage while ensuring good lubrication. Sprayed alkyl-phosphonic acid molecules performed less. They however demonstrated in-situ tribochemical formation of a suspected graphene-oxide based lubricious 3rd body. Grease has been eventually chosen and the satellite successfully launched