Applied Mechanics and Materials Vol. 9

Abstract: The experimental rig of the triple physical pendulum with the first body periodically forced is built. A mathematical model of the real pendulum is created. Friction in joints is modeled as a composition of dry friction and damping. The parameters of the model are estimated matching the output signals from model and experiment. For the minimum searching of the matching function the simplex method is used. Very good agreement between model and real system is obtained. Few chaotic zones are detected numerically and confirmed experimentally.

Abstract: We studied several cases of dynamical problems, where the motion is driven by a concentrated force or distributed load applied at a moving position. The velocity of motion is assumed as constant. In particular, we studied interactions with periodic structure of the medium. Earlier results on one-dimensional structuresare extended to the case of an array of plates.

Abstract: We discuss the dynamic behavior of stepped columns subjected to follower forces. In particular, limit cases which correspond to columns with hinges or cracks and concentrated lateral supports are studied for the stability limit. Typically, solutions suffer jumps in certain derivatives, which have to satisfy compatibility conditions. The influence of these interface conditions on the critical force is investigated. The aim is to optimize the location of such singularities and thus to obtain maximum critical loads, respectively worst case estimates for the loss of stability.

Abstract: With the modern metrology we can measure almost all variables in the phenomenon field of a working machine, and many of measuring quantities can be symptoms of machine condition. On this basis we can form the symptom observation matrix (SOM) intended for condition monitoring. On the other hand we know, that contemporary complex machines may have many modes of failure, so called faults. The paper presents a method for the extraction of fault information from the symptom observation matrix by means of singular value decomposition (SVD) in the form of generalized fault symptoms. As the readings of the symptoms can be unstable, the moving average of the SOM was applied with success. The attempt to assess the diagnostic contribution of primary symptom was undertaken, and also some approach to connect SVD methodology with neural nets is considered. These possibilities are illustrated in the paper by processing data taken directly from the vibration condition monitoring of the machine.

Abstract: We shall discuss the problem of rail vehicle safety studies using simulation methods. The contemporary methods and criteria used for safety assessment of railway vehicles by railways Europe are shown, whereas special attention is paid to the criteria and research programs applied to the vehicle approval procedures in Poland. Taking advantage of these safety criteria and codes of practice, a number of computer simulations have been conducted in order to study the safety issues. Presented results of the computer simulations include a rail vehicle running on a tangent and curved track for different simulation parameters such as: running velocity, load level, condition of wheel profiles, track irregularities. The track irregularities represent different maintenance quality levels which are set according to UIC518 code. In this paper there has also been made a comparison between the results of computer simulation safety assessment studies and the measurements taken in real conditions during the safety tests of a Shimmns(s) type freight vehicle.

Abstract: Certain analytical elastic solution for curvilinear track section under uniform thermal loading has been proposed. Track section is composed of circular arc, transition curves and straight lines. Next step is the analysis of two-dimensional model of the track structure (stress plane, without vertical direction). The rails and the sleepers are assumed as elastic bodies. The fasteners and ballast are modeled as elastic-plastic elements. Non-linear properties of these elements are determined by comparison of numerical data with experimental results. Cyclic uniform thermal field is applied as the load of the system. Pre-buckling analysis is the basic part of the considerations. Certain remarks on the track stability, based on the previous author analyses, are also presented. It is shown that track structure with Y-shaped steel sleepers gives the possibility to use of continuous welded rail (CWR) track practically in any radius of curvature.

Abstract: The paper presents results of numerical simulation for transverse elastic waves corresponding to A0 mode of Lamb waves propagating in a composite plate. This problem is solved by using the Spectral Finite Element Method. Spectral plate elements with 36 nodes defined at Gauss-Lobatto-Legendre points are used. As a consequence of selecting Lagrange polynomials discrete orthogonality guaranteed leading to a diagonal mass matrix. This results in a crucial reduction of numerical operations required for a chosen time integration scheme. Numerical calculations have been carried out for various orientations of reinforcing fibres within the plate as well as for various fibre volumes fractions. The paper shows that the velocities of transverse elastic waves in composite materials are functions of the fibre orientation and the fibre volume fraction.

Abstract: The analysis of friction in brake systems shows a complex dynamic dependence of friction and wear. Friction produces wear but wear affects the surface topography and by that the friction power itself. The wear in technical brake systems causes a dynamic equilibrium of growth and destruction of surface structures on the brake pad, carrying the friction power. This interaction between friction and wear generates a new dynamic friction law, which describes the effects on friction, wear and temperature on different time scales. For very slow processes the friction law reduces to the classical form, describing only the velocity and heat dependence of friction. For unsteady processes the dynamic friction law is able to describe and explain even complex measured friction events in brake systems.