Tadeusz Stolarski

Failure modes of pre-cracked ceramic elements under rolling contact

Abstract A hybrid ceramic/steel angular contact ball-bearing was experimentally modelled using a modified four-ball machine. Ceramic ball surfaces were artificially damaged with ring, lateral and radial pre-cracks. Rolling contact fatigue failure modes were studied under high contact stresses and speeds. The role of lubricant type in rolling contact fatigue failure mode was also assessed.

Running Characteristics of Aerodynamic Bearing with Self-Lifting Capability at Low Rotational Speed

An aerodynamic journal bearing that is capable of self-generating squeeze-film pressure is presented and its dynamic characteristics investigated numerically and experimentally. A numerical method based on a time-marching static model was applied to assess the orbit trajectory path of the rotor upon a perturbation. Experimental results were obtained to validate the effect of the self-generated squeeze-film pressure on the stability of the rotor. Analyzing the Fast Fourier Transform (FFT) responses of the rotor orbits enabled identification of self-excited whirling instabilities. Both numerical and experimental results showed that increasing the squeeze-film effect of the bearing could raise the threshold speed of instability.

Effect of surface roughness on friction behaviour of steel under boundary lubrication

The friction behaviour of grinded and polished surfaces was evaluated by using a reciprocal sliding tester under lubrication with PAO, PAOu2009+u2009ZnDTP and PAOu2009+u2009ZnDTPu2009+u2009MoDTC. Friction coefficients on the smooth surfaces showed higher values compared to those on the rough surfaces. For lubrication incorporating PAO and PAOu2009+u2009ZnDTPu2009+ MoDTC, friction coefficients on both the smoothest and the roughest surfaces decreased with sliding time. On the other hand, friction coefficients between these extremes decreased with sliding time. In this paper, the effects of surface roughness on friction behaviour are discussed.

Some fundamental aspects of self-levitating sliding contact bearings and their practical implementations:

In this study, fundamental aspects and mechanisms of acoustic levitation together with governing equations are presented first. Then, the acoustic levitation phenomenon is considered as a new way to design air suspension systems capable of self-levitation. A particular emphasis is laid on journal bearings and their specific geometrical configuration. A practical feasibility of using acoustic levitation to separate contacting surfaces is supported and illustrated by results of experimental testing of a number of prototype devices.

NFAL Prototype Design and Feasibility Analysis for Self-Levitated Conveying

ABSTRACT In order to avoid friction and scratching when conveying object, an acoustic levitation prototype was designed to verify the feasibility. The modal shapes and the forced harmonic shapes of the prototype are obtained by an ANSYS coupled field computation with a one-quarter symmetry model and the levitation capacity was assessed by the use of groups of simulation and physical testing. The simulation results showed that the pure flexural and mixed flexural wave shapes with different wave numbers existed at some specific frequency. The amplitude in the central point of an aluminum plate having four piezo-electric discs glued to the bottom surface was simulated for a frequency spectrum. The experimental results confirmed the theoretical results and the feasibility of the prototype and confirm that objects can be floated at several resonant frequencies under forced vibrating condition. The system can provide largest bearing capacity when both the piezoelectric disc and the plate resonances coincide.

Performance of Lubricated Sliding Contact in Magnetic Field

Results of experimental studies concerning the influence of permanent magnetic field on wear of lubricated sliding contact operating at short stroke and high frequency are presented. It was found that horizontal magnetic is affecting performance of the contact. The jagged delamination regions produced in the presence of a magnetic field can be regarded as easily undergoing oxidisation because oxygen is readily adsorbed there. Magnetic field is likely to intensify the abrasive action by wear particles and mitigate wear of the plate specimen. It is postulated that all these effects are caused by the influence of magnetic field on the electrical charge of the worn surface created on Si3N4 ball.

Frictional performance of an O-ring type seal at the commencement of linear motion

Results of investigation into the relationship between friction in the O-ring type seal and gauge pressure at the commencement of linear motion of a shaft are presented and discussed. A number of different O-ring materials were studied and the lowest friction under dry conditions was found to be produced by a PTFE-encapsulated silicone seal. The effect of a number of lubricating fluids on friction in the seal was also studied and the results obtained are included.

Microstructure and Residual Stresses in Surface Coatings with PTFE Reservoirs

The paper presents the results of experimental study into the microstructure and changes in residual stresses resulting from sliding and rolling/sliding loaded interaction between metallic surface coatings with embedded PTFE reservoirs and various counter faces. It was found that before testing surface coatings had compressive residual stresses. Molybdenum coating with all types of PTFE reservoirs displayed, as a result of testing, decrease in residual stress level unevenly distributed within the contact path. On the other hand, aluminum–bronze coating, regardless the shape of PTFE reservoirs embedded into it, did not show any appreciable change in the residual stress level due to testing. Residual stresses generated under testing conditions in counter materials were typically of the compressive nature.

Overview of ANSYS structure and its graphic capabilities

This chapter provides a brief introduction to ANSYS as an engineering software suite. Using a GUI (graphical user interface) approach, the most important and basic commands are briefly outlined and illustrated by appropriate screenshots. Easy, step-by-step guidance is given in order to illustrate all vital stages of ANSYS analysis. This begins with launching the programme (naming the project, saving it in an appropriate directory, using various menus available and exiting the programme), preprocessing stage (construction of the model, selection of material, element type, meshing), the solution stage (setting up boundary conditions, applying loads, and running the solution), and finally the postprocessing stage (the general postprocessor, displaying results, error estimation).

Fundamentals of the finite element method

Abstract Various phenomena treated in science and engineering are often described in terms of differential equations formulated by using their continuum. Solving differential equations under various conditions such as boundary or initial conditions leads to the understanding of the phenomena and can predict the future of these phenomena (determinism). Exact solutions for differential equations, however, are generally difficult to obtain. Numerical methods are adopted to obtain approximate solutions for differential equations. Among those numerical methods, those that approximate continua with infinite degree of freedom by discrete body with finite degree of freedom are called ‘discrete analysis’. Popular discrete analyses are the finite difference method, the method of weighted residuals, and the Rayleigh–Ritz method. Via these methods of discrete analysis, differential equations are reduced to simultaneous linear algebraic equations and thus can be solved numerically. This chapter will explain first the method of weighted residuals and the Rayleigh–Ritz method, which furnishes a basis for the finite element method by taking examples of one-dimensional boundary-value problems. The chapter will then compare the results with those by the one-dimensional finite element method in order to acquire a deep understanding of the basis for the finite element method.