PREMIERE ANALYSE DES MECANISMES MOTEURS DE LA FORMATION DES TRANSFORMATIONS TRIBOLOGIQUES SUPERFICIELLES (TTS): EXPERIMENTATION ET MODELISATION DANS LE CAS DU FER PUR

Hachem HAJMOURAD

Hachem.Hajmourad@insa-lyon.fr

Yves BERTHIER

Magali BUSQUET

Laurent BAILLET

Laboratoire de Mécanique des Contacts et des Solides, INSA de Lyon, France

Abstract. Superficial Tribological Transformations (or STT) are usually the less damaging response of materials to tribological conditions by producing the proper solid third body for safe behaviour of ‘dry’ contacts. As a consequence, one solution to control wear is to control STT’s formation. The main objectives of this work are to produce STT (i) in more controlled mechanical conditions than in a contact and (ii) if possible, in a volume which is more important and finally to follow the STT’s formation to identify their driving mechanisms. A Bridgman Anvil Apparatus is used to shear by rotation pure iron cylindrical samples under a quasi-hydrostatic pressure of 1 to 3 GPa. Two STT layers are observed to appear after about 240° of anvil rotation within the ‘skins’ of the sample (i.e. the first 20mm below the surface). The sample structural evolution is analyzed as a function of measured global parameters: the torque (C), the hydrostatic pressure (Ph), the sliding (S) and sample depth (h). This first experimental analysis is coupled with finite element analysis to calculate sample local stresses. Modeling allows better identifying locally different driving mechanisms which control the experiments: volume shearing, material work hardening, interface sliding. The experimentally observed STT areas are directly correlated to a specific calculated behaviour of the sample ‘skin’.

Keywords: superficial tribological transformations, shear plastic flows, pure iron, Bridgman Anvil Apparatus, quasi-hydrostatic pressure.