Key Engineering Materials Vols. 413-414

Abstract: Diagnosis of rolling elements bearing plays an important role on the running and maintenance of mechanical equipments. To enhance the feature of fault and to further diagnose the status of bearings with a small fault size so as to realize the early recognition, the method of inverse filter based on Autoregressive model is presented in this paper, and the corresponding criterion of order selection is also discussed. Analysis of simulation signals and real data show that this method could enhance feature of impulse signal. Meanwhile, it is also found that for small size fault, the root mean square feature is more effective than kurtosis value, which is considered very useful for early diagnosis of rolling elements bearings.

Abstract: In this paper a time-varying identification method is presented, in order to detect the presence of an open crack in a beam with a moving mass travelling on it. The ratio between the considered moving mass and the total mass of the beam is high, thus the identified modal frequencies of the whole structure are time-varying. This situation often occurs when considering the dynamic interaction beetween a train and a bridge and specific identification tools must be used. It is shown that the identification method, referred to here as Short-Time Stochastic Subspace Identification, can give information about the presence of damage in case of time-varying systems.

Abstract: The acoustic emission signals of rolling bearing with different type of defects are de-noised and illustrated by the continuous wavelet transform and scalogram. Morlet wavelet function is selected and the wavelet parameters are optimized based on the principle of minimal wavelet entropy. The soft-threshold de-noising is used to filter the wavelet transform coefficients. The de-noised signals obtained by reconstructing the wavelet coefficients show the obvious impulsive features. Based on the optimized waveform parameters, the wavelet scalogram is used to analyze the real AE signal from the defective rolling bearing in experimental test rig. The results indicate that the proposed method is useful and efficient for signal purification and features extraction.

Abstract: In the context of real-world damage detection problems, the lack of a clear objective function advises to perform simultaneous optimizations of several objectives with the purpose of improving the performance of the procedure. Evolutionary algorithms have been considered to be particularly appropriate to these kinds of problems. However, evolutionary techniques require a relatively long time to obtain a Pareto front of high quality. Particle swarm optimization (PSO) is one of the newest techniques within the family of optimization algorithms. The PSO algorithm relies only on two simple PSO self-updating equations whose purpose is to try to emulate the best global individual found, as well as the best solutions found by each individual particle. Since an individual obtains useful information only from the local and global optimal individuals, it converges to the best solution quickly. PSO has become very popular because of its simplicity and convergence speed. However, there are many associated problems that require further study for extending PSO in solving multi-objective problems. The goal of this paper is to present the first application of PSO to multiobjective damage identification problems and investigate the applicability of several variations of the basic PSO technique. The potential of combining evolutionary computation and PSO concepts for damage identification problems is explored in this work by using a multiobjective evolutionary particle swarm optimization algorithm.

Abstract: As a combination of statistical and mathematical techniques, response surface methodology gives explicit functions to express the relationship between the inputs and outputs of a physical system. This methodology has been widely applied to design optimization, response prediction and model validation but so far little literature related to its application in structural damage identification has been found. Therefore this paper presents a systematic damage identification procedure consisting of four steps of feature selection, parameter screening, primary response surface modeling and updating, reference-state response surface modeling with damage identification realization. 2k factorial design and central composite design are adopted to construct response surface models for parameter screening and model updating purposes, respectively. The proposed method is verified against an experimental reinforced concrete frame and it is found that the proposed method works well in damage prediction.

Abstract: The nonlinear dynamical analyses of a dual-rotor system of an aero-engine are investigated with considering local rub-impacts based on rigid-flexible multi-body simulations. The dual-rotor system is set up from a practical aero-engine prototype, which includes an inner shaft (lower-pressure shaft) and an outer shaft (higher-pressure shaft). The two shafts are in internal-external arrangement and connected by six different rolling bearings. Firstly, a rigid-flexible multi-body model of the dual-rotor system with local rub-impacts is established with MSC.Adams. Then, for the rub-impacts happening between the higher-pressure disk and the fixed elastic rod, the rub-impact forces are described as a nonlinear one with piecewise stiffness and a constant friction. At last, the transverse vibrations of the dual-rotor system are simulated. From the obtained frequency spectra and shaft center orbits of given shaft nodes, many of them are composed of multi-frequencies and demonstrate nonlinear motion patterns.

Abstract: In recent years many SHM approaches based on elastic waves that are generated and sensed by surface-bonded piezoelectric patches have been developed. Some of those utilize wave propagation phenomena; others use changes in the electromechanical impedance to detect structural damage. The capability of most approaches strongly depends on adequate choice of SHM system parameters like excitation signals and actuator/sensor types and positions. For this reason there is a growing interest in efficient and accurate simulation tools to shorten time and cost of the necessary tedious pretests. To detect small damage generally high frequency excitation signals have to be used. Because of this a very dense finite element mesh is required for an accurate simulation. As a consequence a conventional finite element simulation becomes computationally inefficient. A new approach that seems to be more promising is the time domain spectral element method. This contribution presents the theoretical background and some results of numerical calculations of the propagation of waves. The simulation is performed using the spectral element method (SEM), which leads to a diagonal mass matrix. Besides a significant saving of memory this leads to a crucial reduction of complexity of the time integration algorithm for the wave propagation calculation. A new approach to simulate the E/M impedance using time domain spectral elements is shown. An example demonstrates a good correlation of simulation and measurement data, so that the proposed simulation methodology seems to be a promising tool to make impedance based SHM systems more efficient, especially regarding the necessary parameter studies.

Abstract: Nowadays, polyethylene terephthalate (PET) bottles have been increasingly used as drink containers. They are usually manufactured by a stretch-blow molding process. The improper parameters set in the stretch blow molding process may lead to many defects in the stretch-blow bottle. Finite Element (FE) simulations of the forming process were performed in this paper. The influences of the technological parameters, such as the balance between stretching and blowing rate, the movement of the stretch rod and the inflation pressure, were studied. As a result, the defects, such as over-thin area, cracking and deformation, can be predicted by this method. Especially, it is shown that the cracking in the bottom of products may result from the improper values of the dwell time and the stretch rate. The trends shown by the simulation results are in good agreement with the experimental results. The method can be applied to predict the probable defects, assess the structural properties, and optimize the processing parameters of the stretch blow molding process.

Abstract: This paper presents experimental verification and comparison of damage detection methods based on changes in mode shapes such as: mode shape curvature (MSC), modal assurance criterion (MAC), strain energy (SE), modified Laplacian operator (MLO), generalized fractal dimension (GFD) and Wavelets Transform (WT). The object of the investigation is to determine benefits and drawbacks of the aforementioned methods and to develop data preprocessing algorithms for increasing damage assessment effectiveness by using signal processing techniques such as interpolation and extrapolation measured points. Noise reduction algorithms based on moving average, median filter and wavelet decomposition are also tested. The experiments were performed on a 1m long steal cantilever beam. Damage was introduced in form of 10% and 20% deep saw cut, placed in 10%, 30%, 50%, 70% and 90% beam length. Measurements were made using non-contact Scanning Laser Doppler Vibrometer at 125 points equally spaced along beam length.

Abstract: The erosion of the river bed material at bridge pier foundation produced by scour events is one of the main causes of the observed masonry bridges failures and collapses. Foundation settlements and rotations derived from the reduction of the footprint under the piers threaten masonry arch bridges integrity more than any gravity load. The resulting effect on the structure is the development of cracking mechanisms on the arches which may affect the dynamic behaviour of the whole bridge. A scaled experimental model of a masonry arch bridge has been built in the laboratory of the Dep. of Structural Engineering at the Politecnico di Torino. The aim was to better understand scour damage scenario and to identify early structural symptoms of pier erosion. A preliminary dynamic identification is carried out on the intact structure and a comparison with the FEM results is performed. The set of identified modal parameters is adopted as the reference system that will be compared with those acquired after the application of damage of increasing extent.