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

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

Damage detection in beams from modal and wavelet analysis using a stationary roving mass and noise estimation

This paper uses the Continuous Wavelet Transform Analysis on mode shapes for damage identification. The wavelet analysis is applied to the difference in the mode shapes between a healthy and a damaged state. The paper also includes a novel methodology for estimating the level of noise of the experimental mode shapes based on a standard Signal to Noise Ratio (SNR). The estimated SNRs are used for identifying and making emphasis on the less noisy data. Moreover, a mass attached to the structure is considered to enhance the sensitivity of the structure to damage. Modal analysis is performed for different positions of the mass along the beam. The results obtained for all the positions of the mass are combined so an averaging process is implicitly applied. The paper presents the results from an experimental test of a cantilever steel beam with different severity levels of damage at the same location. The results show that the use of the attached mass reduces the effect of noise and increases the sensitivity to damage. Little damage can be identified with the proposed methodology even using a small number of sensors and only the first five bending modesConsejería de Economía, Innovación, Ciencia y Empleo, Junta de Andalucía. Grant Number: P12-TEP-2546Ministerio de Economía y Competitividad. Grant Numbers: BIA2013-43085-P, BIA2016-75042-C2-1-

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

Smart FRP Composite Sandwich Bridge Decks in Cold Regions

INE/AUTC 12.0

Identification of singularities in the displacement field for damage detection in structures

In this thesis, the damage identification problem in beam-type structures through displacement field and the relevant challenges are studied. The exploration includes one damage localization approach using mode shapes and two damage identification methodologies based on static meas-urements. The premise is that concentrated cracks introduce singularities in the displacement fields. The first study on the detecting and locating damage using mode shapes with wavelet analysis is called the Mode Shape-Wavelet approach. The focus is to enhance the sensitivity of the wave-let coefficient to damage. An auxiliary mass was used in the experimental tests to probe the dy-namic characteristics of the beam. The wavelet coefficient of all mode shapes and mass locations are combined as the damage localization indicator. Additionally, a weighting parameter which evaluates the noise effect is formulated into the calculation. The approach is tested with experi-mental mode shapes of a cantilever beam obtained by a set of accelerometers. The investigation using static measurements is based on the deflection difference of the beam prior and posterior to damage. The associated state of the damaged beam that can produce the deflection variation is derived through a superposition scheme and named the Incremental State. Two damage identification methodologies are explored, namely the Deflection-Spring approach and the Deflection-Wavelet approach. The Deflection-Spring approach models the cracks by dis-crete rotational springs and locates them by finding the sudden change in the slope of the deflec-tion difference. Furthermore, the crack depths are estimated through a spring characteristic func-tion. In order to obtained reasonable slope change, a trend estimation for denoising purpose is needed. The Deflection-Wavelet approach locates the damage with a localization index based on the normalized wavelet coefficient for different scales and estimates the damage with a quantifi-cation index developed from the Lipschitz condition. Both methods are tested with experimental data of a simply supported beam. In addition, relevant issues regarding the application in statical-ly indeterminate beams are discussed. The static deflections of the structure in the laboratory tests were measured by a Digital Image Correlation (DIC) system. In the test, a procedure to obtain the whole displacement field of the structure by using partial measurements was explored. The measurements validate this procedure which can facilitate the application for in situ measurement of large scale structures. Lastly, conclusions are drawn and the direction of possible future work is commented to close the thesis

Mathematical and Numerical Aspects of Dynamical System Analysis

From Preface: This is the fourteenth time when the conference “Dynamical Systems: Theory and Applications” gathers a numerous group of outstanding scientists and engineers, who deal with widely understood problems of theoretical and applied dynamics. Organization of the conference would not have been possible without a great effort of the staff of the Department of Automation, Biomechanics and Mechatronics. The patronage over the conference has been taken by the Committee of Mechanics of the Polish Academy of Sciences and Ministry of Science and Higher Education of Poland. It is a great pleasure that our invitation has been accepted by recording in the history of our conference number of people, including good colleagues and friends as well as a large group of researchers and scientists, who decided to participate in the conference for the first time. With proud and satisfaction we welcomed over 180 persons from 31 countries all over the world. They decided to share the results of their research and many years experiences in a discipline of dynamical systems by submitting many very interesting papers. This year, the DSTA Conference Proceedings were split into three volumes entitled “Dynamical Systems” with respective subtitles: Vibration, Control and Stability of Dynamical Systems; Mathematical and Numerical Aspects of Dynamical System Analysis and Engineering Dynamics and Life Sciences. Additionally, there will be also published two volumes of Springer Proceedings in Mathematics and Statistics entitled “Dynamical Systems in Theoretical Perspective” and “Dynamical Systems in Applications”

Framework of damage detection in vehicle-bridge coupled system and application to bridge scour monitoring

Most vibration-based damage identification methods make use of measurements directly from bridge structures with attached sensors. However, the vehicle moving on the bridge can serve as both an active actuator and a response receiver. This dissertation aimed to develop new methodologies to eventually detect bridge damages such as scour using the dynamic response of the vehicle. To reach the final objective, a framework of damage identification was developed first, which gave a guideline on the three crucial steps for damage detection. An optimization method was proposed that combines the Genetic Algorithm (GA) and the First Order (FO) method. It has the advantages of the global and local algorithms and converges faster than the traditional method using any initial values. Secondly, a new methodology using the transmissibility of vehicle and bridge responses was developed to detect bridge damages. The transmissibility of a simplified vehicle-bridge coupled (VBC) system was analyzed theoretically and numerically to study the feasibility of this method. To obtain the transmissibility, two methods were proposed using two “static” vehicles on the bridge. Then, a tractor-trailer test system was designed to obtain reliable responses and extract bridge modal properties from the dynamic response of moving vehicles. The test vehicle consists of a tractor and two following trailers. The residual responses of the two trailers were used, which successfully eliminated the roughness and vehicle driving effect and extracted the bridge modal properties. This methodology was applied on a field bridge and revealed a good performance. Most previous studies of bridge scour focus on the scour causes instead of its consequences. Finally, in this dissertation the developed methodologies were applied to detect scour damage from the response of bridge and/or vehicles. The scour effect on a single pile was studied and methods of scour damage detections were proposed. A monitoring system using fiber optic sensors was designed and tested in the laboratory and is being applied to a field bridge. Finally, the scour effect on the response of the entire bridge and the traveling vehicle was also investigated under the bridge-vehicle-wave interaction, which in turn was used to detect the bridge scour