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International audience; In this work, the influence of aging on the mechanical properties at break of rubber materials are examined. When subjected to physical-chemical aging, the structure of the rubber network is deeply modified through two main mechanisms: crosslinking and chain scission. These aging mechanisms act both on the mechanical behaviour and on the fracture properties of the rubber materials. The goal of this work is to propose a predictive mechanical tool able to give estimates of these mechanical properties. To address this issue, an hyperelastic constitutive model based upon the energy limiter approach, was coupled with physical-chemical parameters in order to capture the whole mechanical behaviour of the damaged materials beyond the fracture. That allows fracture stress and strain estimates. A wide set of materials and experimental data extracted from the literature or obtained in our team were selected based upon the aging mechanism they can exhibit. We found that the elastically active chains concentrations and the swelling rate can be used as relevant indicators of damage either for crosslinking or chain scission process. These parameters are then introduced as damage parameters in the mechanical modelling. The proposed approach leads to very satisfactory predictions, either to capture the whole mechanical behaviour in uniaxial tension or in terms of stress and strain at break estimates.

In this work, the effects of thermo-oxidative ageing at different temperatures and for different exposure durations on the mechanical and the chemical properties of a styrene butadiene rubber (SBR) are presented. Uniaxial tensile tests, hardness measurements, Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy (ATR-FTIR) spectra analysis, and swelling tests are carried out on as-received and aged samples. Accelerated ageing process was conducted at different temperatures ( $$50^\circ C$$ , $$70^\circ C$$ , $$90^\circ C$$ , and $$100^\circ C$$ ) and for different exposure durations $$(7, 14, 21, 28, 35, 45$$ and $$60$$ days).This work confirm that accelerated ageing lead to a decrease of the ultimate mechanical properties and of the molar mass between cross-links in one hand, and an increase of the cross-linking density and of the material hardness, in another hand. ATR-FTIR analysis shows significant changes in the chemical structure of aged SBR samples dominated by the thermo-oxidative process, which is, mainly pronounced at high temperature and long exposure time. The ultimate mechanical properties are related to the average molar mass between cross-links. A threshold value of this property corresponding to a complete degradation of the rubber can be determined. Finally, the time–temperature equivalence principle is applied to build master curves describing the evolution of certain quantities such as molar mass between crosslinks, tensile strength, and strain at break versus the reduced time. A predictive modeling of the stress and strain at break as function of the effective ageing time is proposed which give satisfactory results.

En fatigue des elastomeres, le module de rigidite apparent decroit en fonction du nombre de cycles. Comme phenomene physique, il a ete etabli que pendant chaque cycle, il y a une dissipation d'energie elastique generee par le frottement entre les chaines macromoleculaires a l'echelle de la microstructure de l'elastomere. Cette energie est d'ailleurs en chute permanente durant le chargement cyclique jusqu'a la rupture d'une eprouvette. Ceci engendre une diminution de la rigidite apparente lors d'un chargement cyclique. Dans ce travail nous presenterons une demonstration experimentale et phenomenologique de la chute de la rigidite apparente au cours d'un chargement cyclique en cisaillement pur avec trou. Ensuite nous developperons une relation analytique entre la rigidite apparente et l'endommagement de l'eprouvette.