W. Olszak

On thermal effects in viscoplasticity

ZusammenfassungDas Ziel der Arbeit bildet die Beschreibung der elasto-viskoplastischen Materialien im Rahmen der Thermodynamik von Materialien mit inneren Parametern. Als die thermodynamischen Variablen wurden der Deformationstensor und die Temperatur, als die inneren Parameter die Komponenten des Tensors der inelastischen Deformation eingeführt.Von den konstitutiven Voraussetzungen für elasto-viskoplastische Materialien ausgehend, wurden die Beschränkungen, die das zweite Prinzip der Thermodynamik einführt, untersucht. Der Tensor der inelastischen Deformation wird durch eine linearisierte gewöhnliche Differentialgleichung erster Ordnung beschrieben. Es wurde weiterhin der Relaxationsprozess für ein elasto-viskoplastisches Material diskutiert.

Plasticity Under Non-Homogeneous Conditions

Publisher Summary The theory of plasticity represents one of the branches of rapidly developing continuum mechanics. The progress consists of both a careful analysis of the basic equations and physical relations and an extension of the range of problems and effective solutions covered by this theory. In real media the non-homogeneity of mechanical properties may be caused by numerous phenomena and its nature may be very diverse. First, it is evident that a universal property of bodies occurring in practice is their microscopic non-homogeneity. It is well- known that there have been many successful1 attempts to include microscopic non-homogeneity in the structure of Continuum Theory. The objective of the chapter, however, is the macroscopic nonhomogeneity that is taking place in regions whose linear dimensions are comparable with the characteristic dimensions of the body under consideration. The nonhomogeneity of mechanical properties may be caused, for instance, by phenomena such as the influence of flow of elementary particles, the action of temperature gradients, a nonhomogeneous hardening of the material, different types of surface working, nonhomogeneity of the composition, and so on.

On Elastic/Visco-Plastic Soils

The paper consists of two parts. The first part is devoted to a discussion of the constitutive equations describing the dynamic properties of soils. In the second part, we shall consider the problem of propagation of stress waves in elastic/visco-plastic soils.

On Thermodynamics of the Differential Type Material

The basic object of the present paper is the analysis of the thermodynamic restrictions for the constitutive equations describing simple materials of the differential type. Our approach is based on principles of determinism, local action, material objectivity, equipresence and the second law of thermodynamics.

Les equations constitutives et phenomenes de relaxation dans les milieux elasto/visco-plastiques

SummaryThe paper consists of two parts. The first part is devoted to a discussion of the constitutive equations describing the dynamic properties of soils. In the second part, the relaxation problem in an elastic/visco-plastic soil is considered.

Sur la théorie des phénomènes visco-plastiques

ResuméLa conférence donne un aperçu synthétique de la théorie descorps visco plastiques (reflétant leurs propriétés dynamiques sensibles à la variation de la vitesse de déformation). Quelques exemples d’application sont également discutés (phénomènes de relaxation dans les milieux élasto/viscoplastiques, ainsi que la propagation des ondes de contrainte dans des milieux de ce type). En Gutre, nous généralisons les théories existantes en introduisant une condition de plasticité non-stationnaire (variable dans le temps). Enfin, nous proposons une formulation du critère de plasticité plus générale encore basée sur la notion de l’énergie conservée (accumulée) ainsi que dissipée.SummaryThe lecture presents a synthetic survey on the theory of viscoplasticity (reflecting the rate-sensitive dynamic properties of materials). Some examples of its applications are also discussed (relaxation phenomena occurring in elastic/visco-plastic media as well as the propagation of stress waves in such continua). Besides, we generalize the existing theories by introducing a nonstationary yield condition (variable with time). Finally we propose a further generalization of the yield criterion based on the notion of the conserved (accumulated) as well as the dissipated energy.