16 Décembre – Thesis defense - Sarah Benart
10 h Amphi H - ENSEIRB-MATMECA (Talence)
Mechanistic study of the rubber-to-steel interphase ageing in tires by means of physicochemical and practical adhesion tests.
The present study deals with the durability of the rubber to metal adhesive interphase. The rubber to metal adhesive property is allowed by a thin layer of brass coated on the steel cord surface. During a curing process, the adhesive interphase formation is permitted by sulfur diffusion through the rubber and the growth of sulfide metallic compounds formed with the copper and the zinc coming from the brass coating. During tire life, dioxygen and water are allowed to diffuse through the rubber: the brass coating oxidation and the growth of zinc-rich oxidation products are observed, which leads to an evolution of the rubber to metal adhesive property. The brass to rubber adhesive property has been studied by the mean of the floating roller peel test; its relevance regarding the characterization of the adhesive property evolution has been discussed. Fractures surfaces have been investigated through Raman spectroscopy and SEM-EDS observations in order to discuss the ageing mechanisms of the adhesive interphase. Physicochemical characterization of brass coating has been carried out on pre oxidized samples in a given environment, using electrochemical impedance spectroscopy, Auger electron spectroscopy, Raman spectroscopy and SEM-EDS observations. Relevant electrochemical descriptors have been chosen to predict the coating oxidation resistance. The methodology has been developed on bulk materials (copper, zinc and brass) and then applied on brass coated steel. Relevant ageing conditions for coating oxidation resistance evaluation have been proposed regarding the oxides composition found on fracture surfaces.