Papers by Author: Boris Aberšek

Abstract: The classical methods of solid mechanics assume that the homeomorphism of deformation sometimes does not provide an adequate description of the theological behaviour and fracture of real materials, while irreversible macro deformation and the fracture of solids are predetermined by material behaviour in nanoscale. When we talk about crack propagation, we must talk at least about four phenomena, namely about crack incubation, initiation, and crack propagation must be sleeted in two parts, to growth of short crack and to growth of linear elastic or long crack.

Abstract: For designing machines and devices the dimensioning with respect to service life is increasingly taken into account. This applies also for gearing which are still today one of very important components of almost all machines. The problem of determination of the service life of gearing is directly related to geometry of gears, multiaxial loadings, materials and appropriate models for prediction of the crack propagation. Obviously gears and gearing belong to the real complex structure, by correctly selected and carefully planned experiments we obtained results with which we can confirm and justified the mathematical model for calculating different parameters, i.e. service life.

Abstract: For designing machines and devices the dimensioning with respect to service life is increasingly taken into account. This applies also for gearing which are still today one of very important components of almost all machines. The problem of determination of the service life of gearing is directly related to geometry of gears, multiaxial loadings, materials and appropriate models for prediction of the crack propagation.Obviously gears and gearing belong to the real complex structure, by correctly selected and carefully planned experiments we obtained results with which we can confirm and justified the mathematical model for calculating different parameters, i.e. service life.

Abstract: In this paper, the concepts of preventive maintenance are pres¬ented in first part, and second part of the paper present several mathematical models for prediction service life as a base for preventive maintenance forecasting. These models aid in determining the frequency of inspec¬tions that will allow the condition of a piece of equipment to be determined in order to plan an appropriate maintenance action. The problem of determination of the service life is directly related to geometry, multiaxial loadings, materials and appropriate models for prediction of the failure propagation. The more precise modelling of these input parameters the more precise and reliable the results are. Therefore in the paper we will present models and procedures for calculations service life, remain service life and/or service control cycle.

Abstract: In order to calculate the service life as precisely and reliably as possible we need good mathematical models for describing loading, geometry, properties of materials and fracture mechanics parameters. It can be established whether a mathematical model is precise and reliable only by comparison of results of the method such as analytical methods in case of simple problems and experiment when real complex structure are deal with. Since gears and gearing belong to the second group, by correctly selected and developed test pieces and carefully planned experiments we obtained results with which we confirmed and justified the mathematical model for calculating mentioned parameters. To this end we will show in this paper series of experimental methods and test pieces used on the gears.

Abstract: The optimization is the process of searching for the best results in a certain load case. Complete definition of optimization includes three conditions, which are closely connected: • optimization target, defined with object function, • subject of optimization, • optimization methods. The object functions can be different process parameters such as costs, manufacturing time, costefficiency, productivity etc. In designing of the structures such as a crane there is a tendency particularly towards reducing the weight of steel structures with the same load-carrying capacity. Thus the object function can be the volume, weight or mass of the structure. In the paper we will devote ourselves to optimization of truss structures-gantry crane mean girder by means of the FEM. This method has become indispensable in all areas of analyses of structures in combination with mathematical modeling and mathematical methods of optimization and is particularly of assistance to designers in conceiving the steel structures.

Abstract: This paper presents a control and diagnostics model of single stage gear wheels using acoustic responses. The model is based on various methods and procedures that provide information about the generator’s condition and, specifically, its service life. Four procedures are combined in this model: the mathematical module of the gear wheel that translates the complete mechanical module into mathematical form, the adaptive FIR (Finite Impulse Response) filter that calculates impulse responses from the non-linear system, the module for calculating any impulse response, and the FFT (Fast Fourier Transform) frequency analysis used for simulating frequency spectrums. The result of the simulation is the sound frequency spectrum that allows the analysis of gear wheel tooth damage and, based on this spectrum, calculation of the remaining service life and/or the maintenance process.

Abstract: For accurate determination of the service life we must take into account the loading, which are in most cases random loading of variable amplitude, the geometry and material properties of construction elements which are known not to be constants. The more precise these input parameters are modeled; the more precise and reliable are the results. In our paper we will deal in detail with the model of crack initiation and propagation in the complex structures as a basis of the algorithm for calculating the service life. For determination of the service life for the area of short cracks we used Bilby, Cottrell and Swinden model which is based on the theory of continuously distributed dislocations and we complemented it with random generation of structure of material before cracks. For the long crack we have developed a stochastic model for determination of service life.

Abstract: The paper deals with the problem of service life evaluation of counterweight bar bolted connection by means of computational analysis and experimental testing. Computational analysis has been performed using the local strain-life approach (ε-N), where appropriate material properties for treated high strength steel S1100Q has been determined previously. Experimental fatigue tests of bars were carried out in a specially constructed hydraulic pulsation machine. Comparison of computational and experimental results shows a reasonable agreement.