Grégory Chagnon

A theory of network alteration for the Mullins effect

This paper reports on the development of a new network alteration theory to describe the Mullins effect. The stress-softening phenomenon that occurs in rubber-like materials during cyclic loading is analysed from a physical point of view. The Mullins effect is considered to be a consequence of the breakage of links inside the material. Both filler-matrix and chain interaction links are involved in the phenomenon. This new alteration theory is implemented by modifying the eight-chains constitutive equation of Arruda and Boyce (J. Mech. Phys. Solids 41 (2) (1993) 389). In the present method the parameters of the eight-chains model, denoted C-R and N in the bibliography, become functions of the maximum chain stretch ratio. The accuracy of the resulting constitutive equation is demonstrated on cyclic uniaxial experiments for both natural rubbers and synthetic elastomers.

A comparison of the hart-smith model with Arruda-Boyce and Gent formulations for rubber elasticity

The present paper demonstrates that the Hart-Smith constitutive model and the more recent Arruda and Boyce eight chains and Gent constitutive models are closely related. The ability of these three models to predict both small and large strain responses of rubbers is highlighted and equations that relate their material parameters are established.

The evolution of viscoelastic properties of silicone rubber during cross-linking investigated by thickness-shear mode quartz resonator

Characterizing the effects of cross-linking level and kinetics on the mechanical properties of rubber, especially viscoelasticity, provides information of importance to better understand and predict its final mechanical properties. Classically, the effects of cross-linking on the mechanical properties are investigated with a rheometer. Typical results give the evolution of elastic properties of rubber in the solid state with respect to time or to the cross-linking level. The frequency of the mechanical loading applied is generally a few hertz. In the case where the rubber is initially in the liquid state, such as some silicone rubbers, this type of characterization is not suitable anymore. In this study, a new characterization technique based on the Quartz Crystal Microbalance (QCM) principle has been developed in order to characterize the viscoelastic properties (elastic and viscous moduli) of a silicone rubber during cross-linking, i.e. from the liquid (uncross-linked) to the solid (final cross-linked) state. The device consists in a Thickness-Shear Mode (TSM) resonator generating ultrasonic waves, which provides viscoelastic properties of a material in contact with its surface from an electrical impedance analysis. In contrast to other characterization tools, it makes possible the continuous and non-destructive characterization of viscoelastic properties from a small material volume, under 1mL. Moreover, frequencies at which these properties are characterized are of the order of magnitude of the megahertz, which provides very complementary results to classical characterization, rather in the order of the hertz.