Key Engineering Materials Vols. 293-294

Abstract: The vibration generated by the deformed and unbalanced shaft has caused the damage and the failure of the rolling bearings of worm gears that are coupled by universal joints shaft. These worm gears operate in heavy duty machine. Based on the analysis of the dynamic loads applied to the rolling bearings of worm gear and the measurements of velocities of displacements the reasons of worm gears vibration were determined. The recommendations for avoiding the damage of worm gears are given too.

Abstract: In this paper, mathematical descriptions of the static and dynamic behaviour of the bladed disc with the undamaged and damaged lacing wire are briefly explained. For a steam turbine disc with 70 axial blades coupled by the lacing wire, the centrifugal static analysis is performed. Then, the free and forced vibrations are computed to find differences in vibrations of the bladed disc with and without a failure in the lacing wire. The tip timing measurement is considered as an experimental tool for identifications of possible failures. According to the obtained FE results, a failure of the lacing wire in the rotating disc assembly can be identified by monitoring the centrifugal deformations of the blade tips, resonance frequencies and response amplitudes of the whole bladed disc. The dynamic behaviours of the failure-free disc and with cracked wire connection are compared to each other to outline differences in the known nodal diameter and dispersion curve definition.

Abstract: The paper presents application of the model based diagnostic method for early detection of faults in rotating machinery. The applicability of modal model identification techniques for structural health monitoring of rotating machinery for linear and nonlinear cases is presented. The method based on both operational and experimental (with specially designed active experiment) is discussed. The approach including mapping of nonlinear system to time varying linear one is employed. The theoretical formulation of the method and experimental verification on laboratory rig is shown.

Abstract: An effective approach is presented to eliminate the cross-terms in Wigner distribution by ICA (independent component analysis) and EMD (empirical mode decomposition), through which the cross-terms caused by the uncorrelated mixing signals can be removed successfully. This method is used for time-varying signal analysis and is powerful in signal feature extraction, especially for joint time frequency resolution, which is demonstrated by numerical examples. To further understand the method and its application, a detailed analysis about abrupt unbalance experimental example is shown to explain the cause of malfunction as well as its occurrence and phenomenon. In addition, the proposed approach based upon independent component analysis, empirical mode decomposition method and wigner distribution allows the separation and analysis of the sources with nonlinear and non-stationary properties. In this method, the main conceptual innovations are the associated introduction of ‘source separation’ and ‘intrinsic mode functions’ based on the local properties of the mixed signals, which makes the instantaneous frequency meaningful; the method serves to illustrate the roles played by the nonlinear and non-stationary effects in the energy-time-frequency distribution. At the same time, the method can also be expanded and applied in other fields.

Abstract: Model based fault identification techniques can be used to diagnose local faults in rotating machinery; the equivalent loads that represent fault forces can be used to identify the fault location. But in some cases the equivalent loads smeared over many nodes, and make it hard to identify accurate fault location and transient fault force. In this paper, the fault location is identified using least squares fitting approach by the system’s vibration shape when the fault signal is periodic or quasi-periodic. And after the fault location is ascertained, the transient fault forces can be identified by transient residual vibration using simple matrix multiplications and additions. Numerical simulations and experiment on rotor to stator rub are used to test the method, which proved the efficiency of the method.

Abstract: Aiming at problem on limiting development of machinery fault intelligent diagnosis due to needing many fault data samples, this paper improves a multi-classification algorithm of support vector machine, and a multi-fault classifier based on the algorithm is constructed. Training the multi-fault classifier only needs a small quantity of fault data samples in time domain, and does not need signal preprocessing of extracting signal features. The multi-fault classifier has been applied to fault diagnosis of steam turbine generator, and the results show that it has such simple algorithm, online fault classification and excellent capability of fault classification as advantages.

Abstract: This paper presents a constructive procedure for the identification of a single crack in a beam based on the knowledge of the damage-induced variations in the static deflection of the beam. The crack is simulated by an equivalent rotational spring connecting the two adjacent segments of the beam. The analysis is based on an explicit expression of the crack-induced variation in the deflection of the beam under a given load distribution. The theoretical results are confirmed by a comparison with static measurements on steel beams with a crack.

Abstract: In this paper, a new approach to damage tolerance determination, which is related to the critical rupture strain, is proposed for cylindrical shells subjected to inner transient high-pressure loading. The relation of damage variable and circumferential plastic strain is deduced on the basis of a damage evolution equation as well as a simplified dynamic viscoplastic constitutive equation. The value of damage variable can be obtained then if the strain is known by strain measurement, and the damage tolerance just corresponds to the rupture strain of the structure. Further, the damage tolerance has been applied as the strain-based rupture criterion in the FE simulation of the dynamic fracture process for transient-pressurized cylindrical shells. Especially for the notched shells, the strain concentration effect of notches on the rupture criterion is analyzed quantitatively.

Abstract: This paper describes the design of a rig devoted to testing rolling bearings. In order to control the signal-to-noise ratio of the measures, a potentially very silent test rig has been designed and assembled, with the possibility of simply changing the bearing under investigation as well as its load level and rotating speed. Acceleration data have then been examined by means of envelope, wavelet transform and cyclostationarity analyses, showing that the testing machine fulfils its task.

Abstract: The article presents a method of damage identification in composite rods and beams based on the analysis of changes in Lamb wave propagation. For modelling of the problem the spectral element method is used. Spectral elements of rod and beam suitable for modelling the composites are employed. In the presented paper the following discontinuities are analysed: the fatigue open and not propagating crack, changes in the cross-section area, material discontinuities, various fibres volume and angle. The influence of discontinuities on the Lamb wave propagation processes is analysed.