Applied Mechanics and Materials Vol. 430

Abstract: This paper addresses the suitability of vibration monitoring and analysis techniques to detect different types of defects in roller element bearings. Processing techniques are demonstrated on signals acquired from the test rig with defective bearings. As a result it is shown that there is no reliable universal method for bearing failure monitoring from its early occurence up to bearings failure. Two real life case studies with different types of bearing failures are presented with practical considerations on methods used for failure identification.

Abstract: This paper provides a review of the literature, progress and changes over the years on fault detection of gears using vibration signal processing techniques. Analysis of vibration signals generated by gear in mesh has shown its usefulness in industrial gearbox condition monitoring. Vibration measurement provides a very efficient way of monitoring the dynamic conditions of a machine such as gearbox. Various vibration analysis methods have been proposed and applied to gear fault detection. Most of the traditional signal analysis techniques are based on the stationary assumption. Such techniques can only provide analyses in terms of the statistical average in the time or frequency domain, but can not reveal the local features in both time and frequency domains simultaneously. Frequency/quefrency analysis, time/statistical analysis, time-frequency analysis and cyclostationarity analysis are reviewed in regard for stationary and nonstationary operation. The use of vibration signal processing detection techniques is classified and discussed. The capability of each technique, fundamental principles, advantages and disadvantages and practical application for gear faults detection have been examined by literature review.

Abstract: This paper deals with methods of interpreting the results of vibration measurement to identify structural changes in beam-like structures. We briefly presented an own developed damage assess method, that consider a large number of frequencies for the weak-axis banding vibration modes; it allows first a precise localization and afterwards evaluation of the damages. For the first step, recognition of the damage position, we introduce an algorithm implemented in C++ with the interface done using EXCEL features, indicating by one number the damage probable position, based on the Minkowski metrics. To avoid uncertainties, a graphic representation of all results is also presented. The method is tested for values determined by calculus for a randomly selected location, with and without measurement results debased by noise, proving its reliability.

Abstract: The paper presents a method to assess the crack depth in beams for which the damage location is known. Previous researches lead us to a method to identify damage locations in beams, based on a relation providing frequency changes in respect to damage location and depth. Separating the two variables it is possible to find first the damage location, and afterwards to derive the term controlling the severity. Comparing it with values indicating the frequency shift in respect to damage depth, the severity can be assessed. The paper presents a relation reflecting this dependency for any cross-section type, involving the static deflection for the healthy and damaged beam alone; it has a general character, being not influenced by the cross-section shape.

Abstract: Corrosion as material destruction affects the safety of structures, leading to more serious consequences than the simple loss of a mass. The effect of corrosion on the dynamic behaviour of structures act in two ways: the loss of mass increases the natural frequencies, opposite to the effect of stiffness loss. This paper present the results of researches made to extend the mathematical relation presenting the influence of damage location and severity on the natural frequency changes, by adding the effect mass loss. Therefore we modeled the beam once with the discontinuity and loss of mass, afterwards the damaged segment is replaced by an intact one but having the mass similar to that of the damaged segment. This permitted to plot frequency shift curves for both cases and to contrive the relations defining that curves. Finally a relation summarizing the both effects was contrived; it was confirmed both by numerical simulations and experiments.

Abstract: The purpose of this paper is to determine Young's modulus and the shear modulus of some welded joints made with usual tubular steel by flexural vibration tests. This is the case of the type carbon steel plates S235 JR according to EN 10025, with a thickness of 3 mm welded with MIG/MAG welding process with R713 tubular wire with a diameter of 1.2 mm, using SelcoNeoMig 3500 equipment. The technological part is detailed: welding parameters used, advantages and disadvantages of tubular wires use, problems regarding ambient protection, punctual applications of welding procedures with tubular wire. Processing the obtained signal based on vibration response the elasticity modulus is determined and its value is then compared with the value of elasticity modulus obtained through tensile stress and also with the value obtained by theoretical way.

Abstract: Fireworks are devices containing pyrotechnic composition which, upon functioning, will burn and/or explode to produce a visual or aural effect or movement, or a combination of such effects, intended as a direct form of entertainment.

Abstract: The paper presents the experimental research on concretes and in-situ research on existing reinforced concretes elements, using “Pulse Velocity Method”. The “Pulse Velocity Method” it is an acoustical method which uses the ultra-sounds with 20 to 200 kHz frequency. The in-situ acoustic results are used to establish the durability of the concrete in the tested elements.

Abstract: Climate chambers are a complex system of electromechanical components used for conditioning of air for providing comfort and projected parameters of temperature, humidity, velocity and air cleanliness in the area. In this paper is presented examination of the fan unit company Flaktwoods GJLB-5-071, 17.95 kW, n=1450 rpm, with a multi-functional device Vibrotest 60, the Danish manufacturer Bruel & Kjaer, for diagnostic of parameters of vibration and condition of bearing. The measured parameters are related to: - levels of vibrations (including measurement points on the motor and on the fan) in the directions of coordinate axes, according to ISO 10816-1. - parameters of condition of bearing through the index of bearing condition BCU (Bearing Conditions Unit) and BCS (Bearing Spectrum Conditions) - analysis of the characteristic frequency of vibration in the spectrum, presented by FFT (Fast Fourier Transformation).

Abstract: Measurements of machine vibrations are often influenced by heavy data losses during wireless transmission of signals, which arise because of electromagnetic interference of electric motors. In this paper, authors present an analytic calculation of distortions introduced in spectra of harmonic signals by heavy data transmission losses, which are characterized by the loss ratio and frequency of losses. The results may be used to reduce errors that arise during spectral analysis of signals in conditions of heavy spectral losses.