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Thermomechanics of viscoplastic large strains of solid polymers

Bles G., Gadaj S., Guelin P., Nowacki W., Tourabi A.

Archives of Mechanics

2000

Vol. 52, nr 3

397-427

Experimental results concerning cyclic tension tests performed on polyamid based - braiding samples and on usual samples machined of the same PA66 polyamid are presented. The measurements are thermomechanical: the temperature of the surface of the sample is recorded, resulting in the estimation of the intrinsic internal heat supply. The materials are exhibiting not only the classical viscoelastoplastic behaviour, but also thermomechanical effects of the Kelvin and Taylor-Farren-Quinney type. Modelling based on a previously proposed constitutive formulation of cyclic viscoplastic isotropic behaviour is implemented.

Ratcheting and constitutive patterns of rate-form defined in Preferred Reference Frames

Guelin P., Nowacki W., Quereyron D., Tourabi A.

Archives of Mechanics

1999

Vol. 51, nr 3-4

357-390

A pattern of Rate Form allowing the modelling of the thermomechanical features of the cyclic plasticity has proved to be effective in order to take into account various isotropic behaviours, ranging from those of granular media exhibiting isotropic-deviatoric coupling effects, to those distinguished by shape memory effects or ferrohysteresis ([1] to [8]). Under its basic form, of pure hysteresis type, this discrete memory pattern is able, by definition of a formalism brought into play in the fixed frame and in the A.A. Iliushin space of stress, to describe the behaviour involving perfectly closed cycles. Owing to this fact, it is also unable, in its basic form, to take into account second order effect such as those of multiaxial effects of ratchet type. In order to introduce a well founded and straightforward approach to the continuum thermomechanics of the isotropic solid-like inelastic behaviours, including rate-independent and hardening-independent second order tensorial coupling effects of ratchet type, a new approach is introduced. It is founded on the following assumptions: firstly, the formalism of the initial pattern is not modified, maintaining its role in the A.A. Iliushin spaces of stress and strain (of power and geometry); secondly, the unaltered initial formalism is no longer brought into play in the fixed frame and works now in the Preferred Reference Frame (PRF); thirdly, the definition of this PRF is basically thermomechanical and may be dependent on a mesoscale of Nel-Krumhansl type. The formalism of the general multiaxial isotropic case is introduced and the approach is shown to be straightforward even when the pattern is (easily) generalized to the viscoelastoplastic case. It is shown that the usual multiaxial effect of ratchet type obtained through cyclic torsion is not necessarily hardening-dependent and is existing under zero axial load, in accordance with experimental evidence.