Bernd W. Zastrau

Advanced Contact Mechanics–Road and Rail

The development of contact theories and numerical formula for various applications is a field which expands rapidly. This publication focuses on the rolling contact problem both for tire-road and wheel-rail contact. For the tire-road application a central problem is the modeling of the composite structure of the tire under internal pressure and axle load. One actual contact problem is the rolling on soft soil, which is discussed as the main application. In the wheel-rail case the contact area is much smaller and much more emphasis has been laid on the treatment of material changes, wear and creep phenomena. These approaches are discussed in detail as well as a more recent finite element formulation following the arbitrary Lagrange-Eulerian concept. Ideas about damage mechanisms finish the article.

On the Analytical Solution of Pullout Phenomena in Textile Reinforced Concrete

The bond between the textile reinforcement and the finegrade concrete (cementitious matrix) is essential for the structural behavior of textile reinforced concrete. The analysis of the bond behavior between roving and matrix is important for the development of computational methods analyzing textile reinforced concrete. Therefore, the pullout phenomenon of a roving from a matrix is investigated by analytical methods based on the implementation of various damage models for the interface.

On the Numerical Analysis of the Wheel-Rail System in Rolling Contact

The evaluation of the contact patch and the distribution of stress and strain in rolling contact requires a geometrically and materially nonlinear approach. The presented paper gives an overview over the theoretical background of the Arbitrary Lagrangian-Eulerian formulation of the stationary dynamics of rolling bodies in elastic-elastic contact. Contact formulations for dynamic contact conditions are developed using a velocity oriented approach. The transcription into the Finite Element Method, which is temporarily limited to an elastic material law, is given. For future developments some conceptual comments for the extension for transient rolling contact are made. Numerical examples for three dimensional simulations including rolling over worn profiles demonstrate the applicability of the developed program package. A prospect of started key issues of research and development finalizes the paper.

2D rolling contact problem involving frictional heating

Rolling of an elastic thermoinsulated cylinder on a thermoelastic half-space is investigated. The frictional heating due to the slipping in the contact area is involved. The problem is reduced to a nonlinear system of integral equations which is solved iteratively. The effects of the heat generated on the rolling contact are explored.

An approach for exploring the dynamical behaviour of inhomogeneous structural inclusions under consideration of epistemic uncertainty

Purpose – The purpose of this paper is to analyze the wave scattering behaviour of an inhomogeneous and eccentric inclusion in a homogeneous matrix material. Another purpose is to evaluate the influence of epistemic uncertainty on the wave scattering behaviour, particularly on the lack of knowledge about this eccentricity. This task calls for a multidisciplinary model.Design/methodology/approach – The inclusion is modelled as a multi‐layered obstacle, with all layers being eccentric with respect to each other. The material behaviour of the embedding matrix is linear elastic and isotropic. In a multidisciplinary approach, the interaction of the inhomogeneous inclusion and the embedding matrix with respect to an incoming shear wave of arbitrary shape is solved analytically. The purely analytical solution process takes place in the frequency‐domain. Due to the lack of knowledge about the eccentric configuration of the matrix inclusion and its influence on the total wave field inside the matrix material, the ...

Aspects of Creep Behavior of Textile Reinforcements for Composite Materials~!2009-03-04~!2009-10-15~!2009-12-11~!

Numerous technical applications utilize fiber reinforced composites made with high performance glass and/or carbon fibers. These fibers are especially desirable due to their mechanical and chemical properties resulting in high tensile strength. A relatively new application field is textile reinforced concrete (TRC), which is composed of a textile structure made up of multifilament yarns (rovings) and a cement matrix. To guarantee that the fibers retain their strength over long periods of time in an alkaline milieu, alkaline resistant materials such as alkali-resistant glass fibers (AR-glass) are used. Further requirements placed on textile reinforcements include excellent mechanical properties, such as high strength and stiffness, which remain unchanged or are nominally altered under long-term stresses. These properties will be discussed in this paper within the framework of an experiment conducted, which observed the behavior of AR-glass rovings under continuous long-term stress relative to time. The paper analyzes and interprets the results obtained on the yarns’ mechanical properties. The objective was to develop a mechanical model of the material behavior of the textile structures to aid in the prognosis of long-term behavior of textile reinforced composite materials (i.e. textile reinforced concrete).

On Eigenfrequencies of Multi‐Body‐Systems of MIKOTA‐type

In this contribution the eigenfrequencies of a multi‐body‐system of MIKOTA‐type are investigated. Based on the properties of the mass and stiffness matrices of the chain structured mass‐spring vibration system an algebraic proof for the conjecture of MIKOTA is given.

Numerical Modeling of Textile-Reinforced Concrete

Textile-reinforced concrete (TRC) imposes several special requirements on the applicable simulation methods. TRC is highly heterogeneous at several levels of material structures and, therefore, it exhibits a very complex failure process. Examples of interacting effects are the strain localization due to local failure mechanisms in the yarn, bond, and matrix. As a result, except for standard features, the developed models must be able to reproduce discontinuities of the displacement fields, reflect the irregularity of the material structure, special kinematics relations, and the size effect induced either statistically or energetically. This paper reviews the modeling strategies developed and applied in research and development of TRC in the collaborative research centers in Aachen and Dresden.

CALCULATING THE RIGHT-EIGENVECTORS OF A SPECIAL VIBRATION CHAIN BY MEANS OF MODIFIED LAGUERRE POLYNOMIALS ∗

Abstract This contribution deals with the identification of the right-eigenvectors of a linear vibration system with arbitrary n degrees of freedom as given in [1]. Applying the special distribution of stiffnesses and masses given in [1] yields a remarkable sequence of matrices for arbi- trary n. For computing the (right-)eigenvectors a generalised approach allowing the use of Laguerre polynomials is performed.

Theory and Numerics of a Surface-Related Shell Formulation

The solution of structural analysis problems, especially of shell structures, demands an efficient numerical solution strategy. Since one-sided contact problems are investigated, the shell model is formulated with respect to one of the outer surfaces, i.e. the shell formulation is surface-related. In particular the investigation of textile reinforced strengthening layers [2] will be carried out by this approach.