On the basic laws of anisotropic viscoelasticity

The main aim of this work is to develop a consistent formulation of the rheological behavior for different anisotropic polymer systems. The unified theory of anisotropic viscoelasticity is developed based on the symmetry principles. The Maxwell rheological equation is extended to nonsymmetric anisotropic liquids. Transitions from the most general anisotropy to particular cases of anisotropy are established. It appears that the coupled relaxation of symmetric and antisymmetric stresses is a natural phenomenon in nonsymmetric viscoelasticity. Within the concept of an internal state variable, a stress–order relation is derived for a fully nonlinear case. The order tensor dynamics is also considered. A simple method of deriving the equation of the internal rotational motion is developed for the general macroscopic anisotropy. This paper was presented at the 3rd Annual Rheology Conference, AERC 2006, April 27–29, 2006, Crete, Greece     

Prediction of elastic properties of heterogeneous materials with complex microstructures

The phase-field microelasticity (PFM) is adapted into a homogenization process to predict all the effective elastic constants of three-dimensional heterogeneous materials with complex microstructures. Comparison between the PFM approach and the Hashin-Shtrikman variational approach is also given. Using 3D images of two-phase heterogeneous media with regular and irregular microstructures, results indicate that the PFM approach can accurately take into account the effects of both elastic anisotropy and inhomogeneity of materials with arbitrary microstructure geometry, such as complex porous media with suspended inclusions.     

MHD effects on free convective flow over moving semi-infinite vertical cylinder with temperature oscillation

Numerical solutions of magnetodynamics(MHD) effects on the free convective flow of an incompressible viscous fluid past a moving semi-infinite vertical cylinder with temperature oscillation are presented.The dimensionless,unsteady,non-linear,and coupled governing partial differential equations are solved by using an implicit finite difference method of the Crank-Nicolson type.The velocity,temperature,and concentration profiles are studied for various parameters.The local skin-friction,the average skin-fr...     

Der Einfluß des Zusatzes von Hemicellulosen auf die Fließeigenschaften von Weizenmehlteig

The water adsorption capacity of a dough consisting of wheat flour was increased linearly by the addition of water-insoluble hemicelluloses (xylane, mannane etc.) extracted from beech-wood pulp using soda lye (a by-product of viscose fiber production). The investigation of this finding by viscosity measurements revealed two reasons for the higher water uptake: 1) a higher kneading resistance of the dough, and 2) a gel-regeneration of the kneaded dough during the dough-rest.

Herrn Prof. Dr. Josef Schurz zum 60. Geburtstag gewidmet.     

Method of homogenization applied to dispersion in porous media

The theory of homogenization which is a rigorous method of averaging by multiple scale expansions, is applied here to the transport of a solute in a porous medium. The main assumption is that the matrix has a periodic pore structure on the local scale. Starting from the pores with the Navier-Stokes equations for the fluid motion and the usual convective-diffusion equation for the solute, we give an alternative derivation of the three-dimensional macroscale dispersion tensor for solute concentration. The original result was first found by Brenner by extending Brownian motion theory. The method of homogenization is an expedient approach based on conventional continuum equations and the technique of multiple-scale expansions, and can be extended to more complex media involving three or more contrasting scales with periodicity in every but the largest scale.     

Rolling of a Rigid Cylinder over a Half-Plane with Initial Stresses (Harmonic and Bartenev–Khazanovich Potentials)

An asymmetric quasistationary problem for a prestressed half-plane with harmonic and Bartenev–Khazanovich potentials is solved based of the linearized theory of elasticity. The Mehler–Fock integral transform is used to solve the differential equations that describe the stress–strain state of the half-plane. The dependences of the normal and tangential stresses and stress intensity factors on the elongation are plotted     

Contact Stress Distribution Under a Rigid Cylinder Rolling Over a Prestressed Strip

A nonsymmetric quasistationary problem for a strip with initial stresses is solved under the linearized theory of elasticity for harmonic and Bartenev–Khazanovich potentials. The Hankel integral transform is used to solve the differential equations that describe the stress–strain state of the strip. The dependences of the normal and tangential stresses and stress intensity factors on the elongation are plotted     

Stability of the Sliding Mode in Nonstationary Automatic-Control Systems with Variable Structure

The paper addresses the stability of the sliding mode in nonstationary automatic-control systems of variable structure. The parameters of dynamic states are assumed to vary arbitrarily and continuously within a given bounded domain. The existence and stability conditions for the sliding mode on the switching hyperplane are established. They define nonstationary sets that contain phase velocity vectors directed away from the sliding hyperplane. The sets do not have common points with the switching hyperplane, except for the origin, for the known extreme values of the discontinuous coefficients of logical controls. This is the essence of the necessary and sufficient conditions for the stable sliding mode of the automatic-control system. The general results are used to analyze the stability conditions for the sliding mode in a nonstationary automatic-control system with a variable structure of the third order     

Limit states of elastic–viscoplastic plate deformations caused by repeated shock wave-loadings. Part 1: Experimental observation

In the present work, the evolution of the inelastic centre deflections of shock wave-loaded circular metal plates due to repeated loadings is studied experimentally and numerically. These displacements are compared to those of quasi-statically deformed plates loaded by a pressure equal to the peak pressure of the impulsive loading. Thereby three types of permanent centre deflections are observed: (1) The quasi-statically obtained deflection is exceeded by the middle point displacement of a dynamically loaded structure already after the first impulse and tends towards a limit state after repeated shock wave-loadings. (2) The centre deflection of the impulsively loaded plate exceeds also the quasi-statically caused deflection and does not increase after repeated impulsive loadings any more. (3) The permanent middle point displacement of a dynamically loaded plate is smaller than the deflection of a quasi-statically loaded one and tends towards the middle point displacement of the quasi-static counterpart after repeated shock wave loadings. This phenomenon is known in the literature as ‘Pseudo-shakedown’.

In Part 1 of this study the experimental observation is described, followed by a theoretical study in Part 2.