Miroslaw Wesolowski

Vibration‐based damage detection in a beam structure with multiple damage locations

Abstract During the last two decades structural damage identification using dynamic parameters of the structure has become an important research area for civil, mechanical, and aerospace engineering communities. The basic idea of the vibration‐based damage detection methods is that a damage as a combination of different failure modes in the form of loss of local stiffness in the structure alters its dynamic characteristics, i.e., the modal frequencies, mode shapes, and modal damping values. A great variety of methods have been proposed for damage detection by using dynamic structure parameters; however, most of them require modal data of the healthy state of structure as a reference. In this paper a vibration‐based damage detection method, which uses the mode shape information determined from only the damaged state of the structure is proposed. To establish the method, two aluminium beams containing different sizes of mill‐cut damage at a single location as well as two aluminium beams containing different...

Vibration-based damage identification in laminated composite beams

Vibration-based damage identification in laminated composite beams The basic idea of the proposed vibration-based damage detection method is that a damage as a combination of different failure modes in the form of loss of local stiffness in the structure alters its dynamic characteristics, i.e., the modal frequencies, mode shapes, and modal damping values. A great variety of methods have been proposed for damage detection by using dynamic structure parameters; however, most of them require modal data of the healthy state of structure as a reference. In this paper a vibration-based damage detection method which uses the mode shape information determined from only the damaged state of the structure is proposed. Effectiveness and robustness of the proposed method is demonstrated by two composite beams subjected to different lowvelocity impact energy introduced damage at different locations. The experimental modal frequencies and the corresponding mode shapes for the first 10 flexural modes are obtained by using a scanning laser vibrometer with a PZT actuator. From the mode shapes, mode shape curvatures are obtained by using a central difference approximation. In order to exclude the influence of measurement noise on the modal data and misleading damage indices, it is proposed to use the average sum of mode shape curvature squares for each mode. With the example of the beams with free-free and clamped boundary conditions, it is shown that the mode shape curvature squares can be used to detect damage in the structures. The extent of low-velocity impact introduced damage is identified via the modal frequencies by using mixed numerical-experimental technique. The method is based on the minimization of the discrepancy between the numerically calculated and the experimentally measured frequencies. The numerical frequencies are calculated by employing a finite-element model for beam with introduced damage. Further, by using the response surface approach, a relationship (second-order polynomial function) between the modal frequencies and the damage extent is constructed. The damage extent is obtained by solving the minimization problem.

Damage Identification in Polymer Composite Beams Based on Spatial Continuous Wavelet Transform

In present paper, the damage identification in two polymer composite beams is shown with two methods - spatial continuous wavelet transform (CWT) and mode shape curvature squares (MSCS) using experimental data from operational deflection shapes (ODS). Damage was introduced via low velocity impact drop tower. Statistical hypothesis approach was used to calculate standardized damage index (SDI) that served as a damage indicator for both methods. In order to truncate smaller magnitude SDI peaks, a threshold of 1.28, corresponding to the confidence level of 90%, was applied. Damage estimate reliability (DER) vs wavelet scale test was performed in order to quantify the reliability of damage detection in terms of percentage at each scale parameter. Overall, 78 different wavelet functions were tested. Results indicate that both methods are capable to locate the area of damage.

Damage Identification in Beam Structure using Spatial Continuous Wavelet Transform

In this paper the applicability of spatial continuous wavelet transform (CWT) technique for damage identification in the beam structure is analyzed by application of different types of wavelet functions and scaling factors. The proposed method uses exclusively mode shape data from the damaged structure. To examine limitations of the method and to ascertain its sensitivity to noisy experimental data, several sets of simulated data are analyzed. Simulated test cases include numerical mode shapes corrupted by different levels of random noise as well as mode shapes with different number of measurement points used for wavelet transform. A broad comparison of ability of different wavelet functions to detect and locate damage in beam structure is given. Effectiveness and robustness of the proposed algorithms are demonstrated experimentally on two aluminum beams containing single mill-cut damage. The modal frequencies and the corresponding mode shapes are obtained via finite element models for numerical simulations and by using a scanning laser vibrometer with PZT actuator as vibration excitation source for the experimental study.

Techniques for Non-destructive Material Properties Characterisation

Universal non-destructive techniques, adapted or developed for an effective and accurate characterisation of mechanical properties of composite materials, used in the advanced repair systems of pipelines with volumetric surface defects, are presented. There is static approach using three-points-bending tests and two dynamic methods: impulse excitation and inverse technique based on low-frequency vibrations. An experimental evaluation of the elastic material properties of laminated composites has allowed to validate the examined non-destructive techniques, to demonstrate their simplicity and reliability as well as to define their advantages and limitations.

Modeling and Design of a Full-Scale Rotor Blade with Embedded Piezocomposite Actuators

An optimization methodology for the design of a full-scale rotor blade with an active twist in order to enhance its ability to reduce vibrations and noise is presented. It is based on a 3D finite-element model, the planning of experiments, and the response surface technique to obtain high piezoelectric actuation forces and displacements with a minimum actuator weight and energy applied. To investigate an active twist of the helicopter rotor blade, a structural static analysis using a 3D finite-element model was carried out. Optimum results were obtained at two possible applications of macrofiber composite actuators. The torsion angle found from the finite-element simulation of helicopter rotor blades was successfully validated by its experimental values, which confirmed the modeling accuracy.

Damage identification in beam structure based on thresholded variance of normalized wavelet scalogram

In this paper, a damage identification algorithm based on continuous wavelet transform of one-dimensional structures exploiting mode shapes is presented. Numerical models of aluminium and carbon composite beams, containing a mill-cut and impact damage, respectively are considered for this study. Wavelet scalogram is used to obtain the transform coefficients at different wavelet scales and is subsequently normalized in order to emphasize locations with largest coefficients. Variance of normalized wavelet scalogram is computed along the axis of the beam yielding sharp peaks in the zones corresponding to damage in beams. This operation excludes wavelet scale factors as variables for damage localization problems. The universal threshold is applied to filter out lower amplitude peaks that do not indicate damage. These results are summed up for all nodes of beams and all wavelet functions that are analysed in this paper in order to also exclude the number of different wavelet functions as another variable for damage localization. The universal threshold is applied the second time to yield the final result on the locations of damage. Results suggest that the proposed damage localization method is a fast and reliable tool for damage detection in one-dimensional metal and composite beam structures.

Damage Identification Dependence on Number of Vibration Modes Using Mode Shape Curvature Squares

In this paper a damage identification algorithm for multiple damage sites based on mode shape curvature square method of vibration mode shapes in aluminium beam is reported. The required mode shape curvature of a healthy structure was obtained via interpolation of mode shape curvature of a damaged structure with Fourier series functions of different orders. Algorithm employed calculations of standardized damage index distributions over beam coordinate. Finite element simulations of proposed methodology involving various artificial noise levels and reduction of mode shape input data points were validated on the damage identification results of experimentally measured mode shapes which were measured using scanning laser vibrometer. Results show that the algorithm is capable of capturing the areas of damage. The term called damage estimate reliability was introduced in terms of likelihood of the chosen approximation function to capture the location of damage.

Damping Properties of Sandwich Truss Core Structures by Strain Energy Method

Sandwich panel structures with stiff face sheets and cellular cores are widely used to support dynamic loads. Combining face sheets made of carbon fibre reinforced plastics (CFRPs) with an aluminium pyramidal truss improves the damping performance of the structure due to viscoelastic character of CRFP composites. To predict the damping characteristics of the pyramidal truss core sandwich panel the strain energy method is adopted. The procedure for evaluating the damping of the sandwich panel was performed using commercial finite element software NASTRAN and MATLAB. Non-contact vibration tests were performed on the real sandwich panels in order to extract the modal characteristics and compare them with the numerical predictions.