Smart FRP Composite Sandwich Bridge Decks in Cold Regions

INE/AUTC 12.0

Fractal Dimension Analysis of Higher-Order Mode Shapes for Damage Identification of Beam Structures

Fractal dimension analysis is an emerging method for vibration-based structural damage identification. An unresolved problem in this method is its incapability of identifying damage by higher-order mode shapes. The natural inflexions of higher-order mode shapes may cause false peaks of high-magnitude estimates of fractal dimension, largely masking any signature of damage. In the situation of a scanning laser vibrometer (SLV) providing a chance to reliably acquire higher-order (around tenth-order) mode shapes, an improved fractal dimension method that is capable of treating higher-order mode shapes for damage detection is of important significance. This study proposes a sophisticated fractal dimension method with the aid of a specially designed affine transformation that is able to obviate natural inflexions of a higher-order mode shape while preserving its substantial damage information. The affine transformed mode shape facilitates the fractal dimension analysis to yield an effective damage feature: fractal dimension trajectory, in which an abruptly risking peak clearly characterizes the location and severity of the damage. This new fractal dimension method is demonstrated on multiple cracks identification in numerically simulated damage scenarios. The effectiveness of the method is experimentally validated by using a SLV to acquire higher-order mode shapes of a cracked cantilever beam

Detecting multiple small-sized damage in beam-type structures by Teager energy of modal curvature shape

Detection of multiple damage using modal curvature has become a research focus of great significance in recent years. Nevertheless, a noticeable deficiency of modal curvature is its inadequacy in identifying small-sized damage, which usually results in damage signatures being obscured by the global fluctuation trend of modal curvature. To address this deficiency, this study develops a damage feature of Teager energy of modal curvature shape to identify multiple small-sized damage against the global fluctuation trend of the modal curvature. The advantage of this damage feature over the traditional modal curvature in small-sized damage characterization is first verified in analytical cases of cracked beams with various types of boundary condition, and further validated in a cracked carbon-fiber-reinforced polymer composite beam with the mode shapes acquired using a scanning laser vibrometer

Interpretation of fracture mechanisms in ductile and brittle materials by the Acoustic Emission Technique

Nowadays, the measure of the damage phenomena inside a structure is a complex problem that requires the use of innovative Structural Health Monitoring (SHM) and non-destructive investigation methodologies. The non-destructive method based on the Acoustic Emission (AE) technique has proved highly effective, especially to predict fracture behavior that take place inside a material subjected to mechanical loading. Objective of the research is to use the Acoustic Emission monitoring to evaluate the fracture propagation process during tensile tests, three-point bending (TPB) tests and compression tests. The most representative AE parameters have been measured by sensors in order to obtain detailed information on the wave propagation velocity, signals localization as well as on the dominant fracture mode. As a matter of fact, the waves frequency and the Rise Angle are used to discriminate the prevailing cracking mode from pure opening or sliding. Moreover, the cumulated number of AE events and their amplitude are used to compute the signal energy. For the three-point bending tests on concrete beams, the energy dissipated to create the fracture surfaces and the energy emitted and detected by the AE sensors have been compared on the basis of their cumulative value at the end of the test and their rate during the process loading, in order to investigate on their correlation. A numerical simulation of the mechanical response of the TPB tests has been also performed on the basis of the cohesive crack model. This approach has permitted to obtain a step-by-step evaluation of the crack propagation and a more detailed analysis of the mechanical energy dissipation rate during the loading test. In addition, a dedicated in-situ monitoring at the San Pietro - PratoNuovo gypsum quarry located in Murisengo (AL) - Italy, is started and it is still in progress, developing the application aspects of the AE technique, which has been widely studied from a theoretical and experimental point of view by some Authors in the safeguard of civil and historical buildings. Preliminary laboratory compression tests on gypsum specimens with different slenderness (λ=0.5, λ=1, λ=2) were conducted to assess the validity and efficiency of the system in view to a permanent installation for in-situ monitoring. Currently the quarry is subjected to a multiparameter monitoring, by the AE technique and the detection of the environmental neutron field fluctuations, in order to assess the structural stability and, at the same time, to evaluate the seismic risk of the surrounding area

Vibration analysis of the beam structure under the moving mass

Analytical solution of vibration of simply supported beam under the action of centralized moving mass and two numerical methods using life and death element method and displacement contact method are analyzed in this paper. The results show that vertical acceleration resulted from speed and centrifugal acceleration resulted from load moving must be taken into consideration for large quality and high speed. The characteristics and applicable situations of the two numerical methods are also studied to provide a basis for analyzing and considering structural dynamic problems of moving load mass

Fractal dimension analysis of higher-order mode shapes for damage identification of beam structures

2012-2013 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Dynamic analysis of a simply supported beam with crack

The crack present in the structure changes the physical nature of it as well as changes the dynamic response towards the vibration. For the analysis the depth and location of the crack are important parameters which change the response. So it is important to study these changes for the structural integrity, performance and safety. In the current project titled “Dynamic Analysis of A Simply Supported Beam with Crack” the response nature of both cracked and uncracked beam is predicted. Also the responses for different crack depths are studied. In the present study, vibration analysis is done on a simply supported beam with and without crack. The beam is considered to be an Euler-Bernoulli beam which is the most ideal case for simple calculation. The methods used here are both non-dimensional and parametric. At first the problem was solved using the boundary conditions and the normal equations to find out the natural frequency of the beam. Then the cracked beam was studied taking all the effects of the crack into consideration and the physical property of the material. Here the cracked beam is considered to be two beams connected by a mass less spring at the crack point. The proposed method had been compared with the analytical calculation and then with the help of MATLAB the frequency response had been plotted to see the deviation from the natural response

Singularity detection of 2D signals using fractal dimension analysis of scale information

Fractal dimension (FD) analysis has been widely used in signal processing. The key issue in signal processing is the singularity detection. One of the main problems for FD analysis of signals is its susceptibility to measurement noise, likely obscuring the identification of singularities. To address this deficiency, a new physical quantity, named ‘the scale-window fractal dimension (SWFD)’, is proposed and a SWFD analysis method is formed to identify the singularities in the noisy 2D signal. With this method, the noisy 2D signal first is decomposed into sets of scale signals with the aid of 2D Gabor wavelet transforms; then SWFD estimates are calculated along every scale signals to form the FD surface. The singularities can be localized by the sudden changes in the spatial variation of the FD surface. As an application of the method, the identification of damage singularity for an experimental composite plate is performed with the mode shapes measured by a scanning laser vibrometer as the analyzed 2D signals. The results show that the SWFD analysis method has the prominent features of high accuracy of singularity localization and strong robustness to noise

Singularity detection of 2D signals using fractal dimension analysis of scale information

Fractal dimension (FD) analysis has been widely used in signal processing. The key issue in signal processing is the singularity detection. One of the main problems for FD analysis of signals is its susceptibility to measurement noise, likely obscuring the identification of singularities. To address this deficiency, a new physical quantity, named ‘the scale-window fractal dimension (SWFD)’, is proposed and a SWFD analysis method is formed to identify the singularities in the noisy 2D signal. With this method, the noisy 2D signal first is decomposed into sets of scale signals with the aid of 2D Gabor wavelet transforms; then SWFD estimates are calculated along every scale signals to form the FD surface. The singularities can be localized by the sudden changes in the spatial variation of the FD surface. As an application of the method, the identification of damage singularity for an experimental composite plate is performed with the mode shapes measured by a scanning laser vibrometer as the analyzed 2D signals. The results show that the SWFD analysis method has the prominent features of high accuracy of singularity localization and strong robustness to noise