Percolation thresholds of 3D all-sided percolation clusters in non-cubic domains

The critical 3D all-sided percolation clusters in aL×L×L and aL×aL×L threedimensional domains with a side length L and an aspect ratio a obtained from continuous percolation problem were analysed in this paper. The simulations of continuous percolation were performed in parallelepiped domains starting from a = 1 and ending at a = 10 using the Monte Carlo algorithm. The resulting percolation thresholds for the simulated domains and percolation clusters as well as variability of number of cells in a domain and in a percolation cluster with variation of a were analysed. The obtained results are useful for evaluation of a content of electrically conducting particles in the dielectric matrix of a composite developed for aircraft lightning strike protection purposes

Identification of stiff inclusion in circular composite plate based on quaternion wavelet analysis of modal shapes

The inspection of composite structures is an important process during quality control and their operation in various conditions. Modern industrial requirements of structural condition assessment demand the evaluation of defects using non-destructive and non-contact methods, which allow for detection, precise localization and identification of defect. From a great variety of non-destructive methods the vibration-based ones seem to be effective, simple and low-cost. In order to improve the effectiveness of defects assessment the wavelet-based signal processing technique could be applied. In this paper the modal analysis of a composite circular plate with an inclusion was carried out in order to acquire the modal shapes of vibration. The acquired modal shapes were processed using quaternion wavelet transform. The application of this transform leads to the better directional selectivity than classical discrete wavelet transform. Obtained results allow for detection and identification of location and dimensions of inclusion. The sensitivity analysis of considering particular modal shapes was carried out and described. Due to the effectiveness of the proposed approach it can be applied in laboratory testing as well as industrial quality control and non-destructive testing

Damage assessment in composite structures using modal analysis and 2D undecimated fractional wavelet transform

An interest to novel methods of non-destructive testing (NDT) used for composite structures has been growing during the last decade due to the industrial necessities and development of measurement devices. The promising approach applied for NDT of composite structures is the vibration-based analysis with further processing of measurement data using advanced signal processing techniques, in particular wavelet transforms. In this paper, the 2D undecimated fractional wavelet transform was introduced, which allows for overcoming the problem of initial dataset reduction during performing a wavelet transform. The proposed approach was tested on various composite structures with different types of damages including cracks, delaminations, impact damages in laminates and the core damages and interface damages in sandwich composite structures. Obtained results confirm the effectiveness of the proposed approach and prove the universality of the modal-based NDT with wavelet analysis

Improvement of damage identification ability in composite structures using 2D undecimated fractional wavelet transform

Damage assessment problem in composite structures gained a great importance in recent decades due to the more and more strict demands to the structural safety of aircraft elements. One of the intensively developed methodologies of damage assessment is an approach based on modal analysis and further processing of modal shapes using the wavelet-based methods. During the analysis using discrete wavelet transform the dimensions of spatial domain reduces twice in each direction, which lowers the resolution of resulted patterns. Considering the advantages of application of fractional wavelet transform with fractional B-spline wavelets the algorithm was modified by excluding the decimation process during wavelet-based decomposition. Such a modification allows for obtaining the resulted pattern after decomposition with the same dimensions as an input signal, which improves the localization performance of damages. The advantages of the proposed approach was presented on several examples

Vibration-based damage identification in composite circular plates using polar discrete wavelet transform

Non-destructive damage identification is one of the most important problems in maintenance and reliability of composite structures. The methods applied for damage identification should be sensitive for external and internal damages and provide their precise localization. One of the promising methods for the damage identification is the wavelet transform applied to modal shapes of investigated objects. If the investigated object has circular geometry it is suitable to adapt the algorithm of damage identification to polar coordinate system. The paper presented an application of polar wavelet transform in order to detect and identify various types of damages occurred in composite structures with circular geometry. Several (external and internal) types of damages were considered in the presented study. Basing on comparative study the most adequate polar wavelets for damage identification problems were selected

Characterization of damage evolution during fatigue of composite structures accompanied with self-heating effect by means of acoustic emission

Due to the increasing use of composite materials for load-carrying structures that subjected to high-magnitude cyclic loading or vibrations, it is essential to investigate the accompanying phenomena occurring during structural degradation. The phenomenon, which may significantly accelerate structural degradation is the self-heating effect, causing intensive heating due to mechanical energy dissipation. In order to prevent sudden degradation of composite structures it is essential to characterize occurring damage types and their evolution during fatigue process. In this paper, the determination of fracture mechanisms during fatigue loading was performed based on acoustic emission analysis. The obtained results allow for clustering of acoustic emission data by type of occurring damage and correlate it with accompanying self-heating appeared during loading. This allows for proper understanding of physics of observed phenomena, which may help in design and operation of composite structures subjected to fatigue loading accompanied with self-heating effect

Influence of parameters of modal analysis on vibration-based structural damage detectability

Vibration-based non-destructive testing (NDT) is one of the most widely used diagnostic methods of composite structures. The parameters of modal analysis may affect the accuracy of damage detectability, localization and identification. The aim of this paper is to investigate an influence of such parameters on results obtained after modal analysis of a composite structure and wavelet-based processing. Four parameters were taken into consideration: a frequency resolution of a frequency response function, a number of averaging cycles, a type of an excitation signal and a number of measurement points. The series of tests were performed on a composite sandwich structure with a honeycomb-type core using scanning laser Doppler vibrometer. The discussed results can be considered as recommendations for performing NDT of composite structures using vibrations in terms of parameters of modal analysis

Automated wavelet-based damage identification in sandwich structures using modal curvatures

Recently, damage assessment of composite structures being in operation has been one of crucial problems in industries such as aircraft, aerospace, automotive, etc. Following this, rapid development of non-destructive testing methods has been observed over the last decades. One of the promising approaches is vibration-based one, which in general is based on identification of a damage using singularities in modal shapes of vibration. The identification procedure requires application of advanced signal processing techniques, where the wavelet transform is used the most commonly. Due to the high sensitivity of wavelet-based approach to changes of parameters of an analysis, e.g. a type of applied wavelet and its order, it was decided to develop an algorithm, which allows automating this process by using multi-objective meta-optimization of the mentioned parameters. The presented approach allows selecting optimal parameters for wavelet-based damage identification procedure without neither a priori knowledge on values of wavelet parameters, nor the parameters of an optimization algorithm. The proposed approach was tested on composite sandwich structures with damaged core as well as damaged face sheets. Obtained results confirm the effectiveness of automated damage identification mainly in the context of the high convergence to the optimal solution

Detection of structural changes in concrete using embedded ultrasonic sensors based on autoregressive model

International audienceEmbedded ultrasonic transmission measurements can be a cost effective and more user-friendly alternative in comparison to commonly used structural health monitoring systems used in civil engineering to detect operational or environmental changes in structure. They can be used to detect small structural changes in large concrete structures without necessity of placing a sensor on the spot where the changing is taking place. This paper presents the investigations on the possibility of utilising autoregressive model, where the velocity of ultrasonic wave in a medium is dependent on the operational state. The goal is to use the model for localization of operational changes in the large concrete structure by means of embedded ultrasonic transducer networks. In this study, several static load tests and dynamic test on large reinforced concrete beams have been performed using embedded ultrasonic sensors. Using the autoregressive model it is possible to localize operational changes in the concrete structure. The proposed approach of diagnostic signal processing allows for precise evaluation of structural changes in concrete

Characterization of damage evolution during fatigue of composite structures accompanied with self-heating effect by means of acoustic emission

Due to the increasing use of composite materials for load-carrying structures that subjected to high-magnitude cyclic loading or vibrations, it is essential to investigate the accompanying phenomena occurring during structural degradation. The phenomenon, which may significantly accelerate structural degradation is the self-heating effect, causing intensive heating due to mechanical energy dissipation. In order to prevent sudden degradation of composite structures it is essential to characterize occurring damage types and their evolution during fatigue process. In this paper, the determination of fracture mechanisms during fatigue loading was performed based on acoustic emission analysis. The obtained results allow for clustering of acoustic emission data by type of occurring damage and correlate it with accompanying self-heating appeared during loading. This allows for proper understanding of physics of observed phenomena, which may help in design and operation of composite structures subjected to fatigue loading accompanied with self-heating effect