Rims Janeliukstis

Fatigue Life Assessment Method for Prestressed Concrete Sleepers

Concrete sleepers are one of the most important applications of a railway track system. Researchers have previously studied the impact load characteristics and ultimate load carrying capacity of a prestressed sleeper but research on the fatigue life of prestressed concrete sleepers is limited. Prestressed concrete sleeper fatigue damage is mainly due to the accumulation of defects, caused by the repeated load of wheel-rail interaction. Fatigue load, fatigue characteristics and the existing design methods of prestressed concrete sleeper are summarized in this paper. The commonly used fatigue assessment methods of concrete structures are also evaluated. Based on the results of former research result, this article presents a convenient fatigue life assessment method for a prestressed concrete sleeper, and contrasts with the test results. The insight information gained can be used to evaluate the service performance and predict the fatigue life of the concrete sleeper, as well providing design flexibility and broadening the design principle. The outcome of this study may also improve the rail track maintenance and inspection criteria, in order to establish an appropriate track condition monitoring network in practice.

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.

Application of metal coatings for functionalization of technical fibers and fabrics

The metal coatings in combination with sonochemical and leaching processes are used for nanostructuring and functionalization of glass, flax and hemp fabrics. The leaching is used for nanostructuring sodium alumosilicate K-glass fabrics to obtained silica like fibre with nanoporous structure on surface and in volume. The natural fibres as well as fabrics themselves are porous media. The porous media adsorbs water and content of moisture in fabrics have to be controlled. The metal-coated fabric characterization is an actual problem. Application of metal coatings for the functionalization of technical fibres and fabrics faced with influence of moisture on functional properties, e.g., the impedance of the metal coated K-glass and flax and hemp fabrics have strong dependence of content absorbed water or moisture. Presented studies are on the moisture content determination methodology based on fhermogravimetric analyses and impedance spectroscopy. The leached K-glass fibres have three absorption sites with different kinetic and desorption heat. The flax has more complicated distribution of sorption/desorption sites. The water desorption heatl,3 kJ/g for both type of fabrics in temperature range 30–150 0C is comparable to the water evaporation heat 2,3 kJ/g at 100 0C. For leached K-glass fibre from the isothermal nitrogen sorption/desorption plot the pore volume is up to 7.5 cm3/g. and pore sizes are in range 2-100 nm.

Localization of Impact Damage in Thin-Walled Composite Structure Using Variance-Based Continuous Wavelet Transform

This work is focused on damage localization in thin-walled two-dimensional composite structures. A two-stage low-velocity impact damage with severities of 5 and 9 J is applied to CFRP plate in different positions and a dynamic vibration test is conducted in order to extract the resonance frequencies and corresponding deflection shapes of the structure before and after each stage of damage. Deflection shapes serve as an input for spatial continuous wavelet transform in two dimensions to calculate the damage index and standardize it for every wavelet function. Overall, 16 wavelet functions are used with scale parameters ranging from 1 till 16. The nontrivial problem of scale selection is avoided by computing the variance of normalized scalogram (VNS) over all the scales of consideration for every wavelet. Cross-correlation of VNS values between all the wavelets is performed to reveal the wavelet pairs of similar performance. These wavelet pairs are selected to compute the average VNS (AVNS). Later, a universal threshold is applied to filter the peaks of AVNS to yield the location of damage for each case of severity. Results suggest that a damage can be localized without the consideration of a specific wavelet and scale parameter.

Classification Model for Damage Localization in a Plate Structure

The present study is devoted to the problem of damage localization by means of data classification. The commercial ANSYS finite-elements program was used to make a model of a cantilevered composite plate equipped with numerous strain sensors. The plate was divided into zones, and, for data classification purposes, each of them housed several points to which a point mass of magnitude 5 and 10% of plate mass was applied. At each of these points, a numerical modal analysis was performed, from which the first few natural frequencies and strain readings were extracted. The strain data for every point were the input for a classification procedure involving k nearest neighbors and decision trees. The classification model was trained and optimized by finetuning the key parameters of both algorithms. Finally, two new query points were simulated and subjected to a classification in terms of assigning a label to one of the zones of the plate, thus localizing these points. Damage localization results were compared for both algorithms and were found to be in good agreement with the actual application positions of point load.

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.

DYNAMIC AMPLIFICATION FACTORS FOR RAILWAY TURNOUT BEARERS IN SWITCHES AND CROSSINGS

Railway infrastructure is nonlinear by nature, scientifically proven by its behaviours, geometry and alignment, wheel-rail forces and operational parameters such as tractive efforts. It is often found that most train-turnout interaction models do not consider the time dependent ballast degradation. Such ballast degradation later causes differential settlement and aggravates impact forces acting on partial and unsupported sleepers and bearers. Furthermore, localised ballast breakages underneath any railseat increase the likelihood of centre-bound cracks in railway sleepers and bearers due to the unbalanced support. This paper presents a numerical simulation of a standard-gauge concrete bearer at crossing panel, taking into account the tensionless nature of ballast support. The finite element model was calibrated using static and dynamic responses using past experiments. In this paper, the influences of topologic asymmetry on dynamic amplification behaviours of crossing bearers under impact loading are firstly investigated. In addition, it is the first to demonstrate the effects of sleeper length on the design consideration of turnout bearers in crossing panel. The outcome of this study will improve the railway turnout construction and maintenance criteria in order to improve train-turnout interaction and ride comfort. Sakdirat Kaewunruen, Chayut Ngamkhanong, Rims Janeliukstis and Ruilin You

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.