1,720,987 research outputs found
Ultrasonic guided wave monitoring of composite wing skin-to-spar bonded joints in aerospace structures
No full textThe monitoring of adhesively bonded joints by ultrasonic guided waves is the general topic of this paper. Specifically, composite-to-composite joints representative of the wing skin-to-spar bonds of
unmanned aerial vehicles "UAVs" are examined. This research is the first step towards the development of an on-board structural health monitoring system for UAV wings based on integrated ultrasonic sensors. The study investigates two different lay-ups for the wing skin and two different types of bond defects, namely poorly cured adhesive and disbonded interfaces. The assessment of bond state is based on monitoring the strength of transmission through the joints of selected guided modes. The wave propagation problem is studied numerically by a semi-analytical finite element method that accounts for viscoelastic damping, and experimentally by ultrasonic testing that uses small PZT disks preferably exciting and detecting the single-plate s0 mode. Both the models and the experiments confirm that the ultrasonic energy transmission through the joint is highly dependent on the bond conditions, with defected bonds resulting in increased transmission strength. Large sensitivity to the bond conditions is found at mode coupling points, as a result of the large interlayer energy transfer
Global-Local model for guided wave scattering problems with application to defect characterization in built-up composite structures
No full textPredicting scattering of elastic guided waves in multi-layered solid plates with geometrical and/or material discontinuities is of great interest to many fields, including ultrasonic-based Non-Destructive Testing (NDT) and health monitoring of critical structural components (SHM). The problem is complicated by the multimode and dispersive behaviour of the guided waves. This paper describes a unified Global-Local (GL) approach that is computationally efficient in cases that can be very complex in terms of geometry and/or material properties. One example of this is a composite built-up structure. The proposed GL procedure discretizes the “local” region with the scattering discontinuity by regular finite elements, and utilizes the efficient Semi-Analytical Finite Element solutions in the “global” region away from the scatterer. The GL formulation that is presented includes the dispersive unforced solutions for each applicable mode, the mode tracking, the scattered spectra (reflection and transmission), and the energy balance calculations. The algorithm is applied to the case of a composite skin-to-stringer assembly used in modern aircraft construction. Various representative defects in this assembly are modelled, and transmission spectra are calculated for both axial or flexural guided wave modes used in excitation. The resulting scattered spectra (which are the broadband transfer functions of the structure) can be useful to either select suitable wave mode-frequency combinations or to identify specific defects in guided-wave NDT or SHM tests of these components
Modeling guided wave propagation with application to the long-range defect detection in rail road tracks
No full textRecent Advancements in Global-Local Analysis of UGW in Plates
No full textThe use of ultrasonic guided waves (UGWs) has increased considerably for NDE and SHM purposes. Analytical solutions are available for few cases only, namely for waveguides of uniform cross-section and in the presence of simple defects. For more complex structural configurations, materials or defects, numerical methods are indispensable. A good compromise is coupling analytical solutions with numerical methods, as in the proposed hybrid Global-Local (GL) method. An eigenvalue problem in the framework of the Semi Analytical Finite Element method (SAFE) is posed to solve for the complex wavenumber and wavemodes, that are then propagated analytically in the wave propagation direction. To include scattering and wave propagation from the UGW interaction with geometrical discontinuities, damages, and any changes along the wave propagation direction, SAFE is coupled with other computational approaches such as full FEM in this work. The complexity of UGW scattering is increased by the presence of propagating and non-propagating modes, the latter becoming significant in the near-field effects, i.e. in the vicinity of defect edges. This work shows the advantages of including the evanescent modes in the accurate modeling of UGWs scattering through applications on isotropic aluminum plates
Global–local model for three-dimensional guided wave scattering with application to rail flaw detection
Get PDFThis study presents a three-dimensional global–local formulation for the prediction of guided wave scattering from discontinuities (e.g. defects). The approach chosen utilizes the Semi-Analytical Finite Element method for the “global” portion of the waveguide, and a full Finite Element discretization for the “local” portion of the waveguide containing the discontinuity. The application of interest is the study of guided wave scattering from transverse head defects in rails. Theoretical scattering results are impossible to obtain in this case for a wide-frequency range. While three-dimensional Semi-Analytical Finite Element–Finite Element models for guided wave scattering studies have been used in the past, this is the only study where guided waves in rails were modeled in a wide-frequency range (up to 180 kHz). A comparison analysis with a benchmark study of wave reflections from the free end of a cylindrical rod is conducted first. For the case of the rail, selected case studies of incoming guided modes were chosen, and reflection and transmission spectra are calculated for head defects of various sizes. This kind of results can be utilized to guide and/or interpret ultrasonic guided wave tests aimed at defect detection or quantification. Finally, parametric studies are conducted to examine more closely the role of certain operational parameters that are important in this kind of analysis, and specifically the size of the “local” region and the number of guided modes considered. These parametric studies lead to compromises that need to be struck on the basis of conservation of energy among all wave modes involved
The Global-Local Approach for Damage Detection in Composite Structures and Rails
No full textStructural components with waveguide geometry can be probed using guided elastic waves. Analytical solutions are prohibitive in complex geometries, especially in presence of structural discontinuities or defects. The Global-Local (GL) approach provides the solution by splitting the waveguide in “local” and “global” regions. The “local” region contains the part of the structure responsible for the complex scattering of an incident wave. What happens in this region cannot be reproduced analytically. The “global” region is regular and sufficiently far from the scatterer, in order to exploit known analytical wave propagation solutions. The proposed GL approach discretizes the local region by regular finite elements, and utilizes the efficient Semi-Analytical Finite Element (SAFE) method in the global region. Kinematic and mechanical constraints ensure the displacements and stresses continuity at the global-local interface. The evaluation of the energy of reflected and transmitted waves is used to check the before-after scattering energy balance. Numerical results are shown with regard to the specific cases of a composite skin-to-stringer assembly used in modern aircraft construction and a railroad track with a common section. The effects of different damage configurations are analyzed in both cases studying the reproduced scattered spectra related to specific incident waves. The results can be useful to select the best incident mode-frequency range in order to best identify specific defects in these structures
Extraction of thermal Green's function using diffuse fields: A passive approach applied to thermography
No full textIn the field of non-destructive evaluation, defect detection and visualization can be performed exploiting different techniques relying either on an active or a passive approach. In the following paper the passive technique is investigated due to its numerous advantages and its application to thermography is explored.In previous works, it has been shown that it is possible to reconstruct the Green's function between any pair of points of a sensing grid by using noise originated from diffuse fields in acoustic environments. The extraction of the Green's function can be achieved by cross-correlating these random recorded waves. Averaging, filtering and length of the measured signals play an important role in this process. This concept is here applied in an NDE perspective utilizing thermal fluctuations present on structural materials. Temperature variations interacting with thermal properties of the specimen allow for the characterization of the material and its health condition. The exploitation of the thermographic image resolution as a dense grid of sensors constitutes the basic idea underlying passive thermography. Particular attention will be placed on the creation of a proper diffuse thermal field, studying the number, placement and excitation signal of heat sources. Results from numerical simulations will be presented to assess the capabilities and performances of the passive thermal technique devoted to defect detection and imaging of structural components
Non-contact ultrasonic inspection of rails and signal processing for automatic defect detection and classification
No full textRecent train accidents, associated direct and indirect costs,
as well as safety concerns, have reaffirmed the need for
developing rail defect detection systems more effective than
those used today. One of the recent developments in rail
inspection is the use of ultrasonic guided waves and noncontact
probe techniques to target transverse-type defects.
A rail inspection prototype based on these concepts is under
development at University of California at San Diego (UCSD.
This work reports on the feature extraction and automatic
pattern recognition algorithms that are being tested in the
laboratory and will be added to the prototype. The results
demonstrate the detection and sizing of transverse, surfacebreaking
cracks that extend for less than 20% of the rail
head cross-sectional area
High-velocity Impact Location on Aircraft panels Using Macro-fiber Composite piezoelectric Rosettes
No full textIn this article, an approach based on an array of macro-fiber composite (MFC)
transducers arranged as rosettes is proposed for high-velocity impact location on isotropic and
composite aircraft panels. Each rosette, using the directivity behavior of three MFC sensors,
provides the direction of an incoming wave generated by the impact source as a principal
strain angle. A minimum of two rosettes is sufficient to determine the impact location by
intersecting the wave directions. The piezoelectric rosette approach is easier to implement than
the well-known time-of-flight-based triangulation of acoustic emissions because it does not
require knowledge of the wave speed in the material. Hence, the technique does not have the
drawbacks of time-of-flight triangulation associated to anisotropic materials or tapered sections.
The experiments reported herein show the applicability of the technique to high-velocity
impacts created with a gas-gun firing spherical ice projectiles
A match coefficient approach for damage imaging in structural components by ultrasonic synthetic aperture focus
Get PDFUltrasonic Synthetic Aperture Focus (SAF) techniques are commonly used to image structural defects. In this paper, a variation of SAF based on ideas borrowed from Matched Field Processing (MFP) is evaluated to reduce artifacts and sidelobes of the resulting images. In particular, instead of considering the full RF ultrasonic waveforms for the SAF time backpropagation, only selected features from the waveforms are utilized to form a “data vector” and a “replica” (expected) vector of MFP. These vectors are adaptive for the pair of transmitter-receiver and the focus point. The image is created as a matched filter between these two vectors. Experimental results are shown for an isotropic and homogenous metallic plate with simulated defects, probed by six piezoelectric patches used as receivers or transmitters
- …
