Piotr Marek

Residual stress in some elasto-plastic problems of rolling contact with friction

Abstract The problem or rolling contact is of a great interest from the practical and cognitive points of view. It concerns for example a wheel passage on a rail, as well as many other processes where rolling or rolling with sliding is involved. Particularly, residual stresses distributions in the subsurface area due to plastic deformations are of significant importance: these stresses strongly influence fatigue limit and cracking tendencies of the material. A motion of the wheel on the rail (or of a roller on a strip) often has a very complex character: it consists of rolling, sliding in the longitudinal direction due to brakings and accelerations, sliding in the transversal direction, etc. Investigations conducted on this field by many authors have not yet delivered a unique solution. The aim of this paper is to determine the influence of some of these components of the wheel motion (separately and in common action) on residual stresses distributions. The problem has been investigated numerically by the FEM method, using the program SEGLA developed by the authors. The program can be applied to solving linear and nonlinear 2D, axisymmetric and 3D problems with elasto-plastic effects in the nonlinear contact and fracture mechanics. It uses three, four, six, eight and nine-node elements and also the special “spring” elements to model contact. The applied algorithm allows automatic analysis of these fragments of boundary, which enter and leave the contact; in the area where the “new” contact is created the program introduces additional elements.

Development of plastic zones and residual stress in elasto-plastic contact problems with stress singularities in elastic range

Abstract Stress singularities appear in such elastic contact problems as a plane indenter compressing a semi-infinite body, or the axisymmetric case of a turbine disc shrunk onto a shaft. The stress is infinite at the edge of the corner of the indenter and the disc as well as in neighbouring areas of the semi-infinite body and the shaft. In this paper the complex investigation of the distributions of plastic zones, deformations, pressure and residual stress has been presented for plane indenters of different shapes being in elasto-plastic contact with semi-infinite bodies. Different strain-hardening characteristics of the material, different yield criteria and states of stress/strain have been considered. The aim of the investigation is to find an answer to the question, what happens to the stress singularity, which appears in the elastic solution? The considered problem is of interest from the cognitive point of view and is of real importance in engineering practice.

On methods of reduction and elimination of stress singularities in some elastic contact problems

Abstract Stress singularities appear in such elastic contact problems as an indenter compressing a semi-infinite body, or the axisymmetric case of a turbine disc shrunk on to a shaft. The stress is infinite at the edge of the sharp corner of the indenter and the disc, as well as in neighbouring areas of the semi-infinite body and the shaft. In this paper, the changes in the nature of singularities and stress distributions have been determined numerically and experimentally for different ways of shaping the indenter, the semi-infinite body and the interface. Contacts with and without friction have been considered. The aim of the investigation is to find a shape which either totally eliminates the singularity or essentially limits the area of stress increase, diminishing radically the stress concentration factor at some chosen distance from the corner. The considered problem is of interest from the cognitive point of view and is of some importance in engineering practice.