Contents of Journal of Mechanical Engineering 53, 1 (2002)

J. FIALA, I. SCHINDLER, R. FORET, S. NEMECEK: Examination of engineering materials structures and its degradation by X-ray diffraction (in Czech) 1 M. KARAS, A. P. ZIELINSKI: Hybrid Trefftz least square element for plane elasticity 24 B. SAMANTA, S. A. AL-ARAIMI, R. A. SIDDIQUI: A neural network approach to estimate fatigue life of 6063 aluminum alloy 36 L. PUST, A. SKUDEROVA: Damping induced into vibrating system by a limited energy source 45


Examination of engineering materials structure and its degradation by X-ray diffraction


The goal of this paper is to draw attention to an X-ray diffraction (XRD) technique which allows to obtain very useful data on the internal structure of materials. The technique consists in the examination of the azimuthal (lateral) diffraction line profile, i.e. the size, number and shape of individual diffraction spots that discontinuous diffraction line consists of. Each spot represents the diffraction image (topograph) of a definite crystallite (the orientation of which meets the Bragg condition) and provides information on the size, shape and orientation of this crystallite. Such an information is not easy to obtain by other methods and can be advantageously used in the development and optimization of technological processes. Another domain in which this method can be usefully exploited is monitoring of processes which degrade the materials structure in course of their service and predicting the residual life-time of the products and construction parts made of them. The recent development of the instrumentation technology (area electronic position-sensitive detectors and polycapillary collimators) provides the base for an extensive employment and a great boom in the usage of this XRD technique for the characterization of materials structure at the onset of the third millennium.

Hybrid Trefftz least square element for plane elasticity


The Hybrid Trefftz (HT) element with the least square formulation for plane elasticity problems is presented and compared with the well-established HT Displacement element. The convergence of the solution is carefully studied (in the global and local sense). Numerous tests proving the efficiency of the element are presented.

A neural network approach to estimate fatigue life of 6063 aluminum alloy


A procedure is presented to estimate fatigue life of Aluminum-Magnesium-Silicon (Al-Mg-Si) 6063 alloy using a neural network based approach. The aluminum alloy samples were heat-treated and aged at different combinations of temperature and time. The samples were tested to obtain fatigue life. The normalized data of ageing conditions were used as inputs to an artificial neural network (ANN) with the corresponding fatigue life data as target outputs. The ANN was trained using backpropagation algorithm with a subset of the experimental data and tested with the remaining set of data. The results show effectiveness of the ANN in estimating fatigue life of 6063 aluminum alloy for different ageing conditions. The results of ANN are found to be better than that of multiple regression analysis.

Damping induced into vibrating system by a limited energy source


Influence of a joined engine on the mechanical system was very often studied only from the point of stability of forced vibrations in resonance zone (so called Sommerfeld effect). Very small attention was paid to the increased damping of the whole system.

In this paper, the dynamic properties of a very simple torsional undamped system connected by a driving motor with limited power are studied. The courses of the eigenfrequencies and response curves of such a system are presented and analyzed. The induced damping depends on the slope of the driving motor as well as on the structure of the system, and it can reach even aperiodic damping.