Self-Focusing of Rayleigh Waves and Lamb Waves with a Linear Phased Array

Deutsch, W. A. K.; Cheng, A.; Achenbach, J. D.

doi:10.1080/09349849708968122

Cited by 5 publications

(5 citation statements)

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“…In the 'soft connection', there are usually three independent nodes located at one delamination front location, in which two are on the neutral planes of the upper-and lower-delaminated layers, and one is on the neutral plane of the intact side. In this case, the displacement continuity conditions for three translational displacements, i.e., u, v, and w, are constructed by using the displacement and rotation information on both sides around the delamination front, through, e.g., Equation (5). Because the rotations at the three nodes are completely independent, this technique leads to a soft structure.…”

Section: Validations Experimental and Numerical Analysis Procedures For Cfrp Beamsmentioning

confidence: 99%

Optimal Excitation Frequency of Lamb Waves for Delamination Detection in CFRP Laminates

Liu

et al. 2009

Journal of Composite Materials

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To improve the reliability of delamination detection techniques based on Lamb waves for carbon fibre reinforced plastics (CFRP) composite laminates, the influence of excitation frequency of Lamb waves on the intensity of reflected waves from a delamination in cross-ply CFRP delaminated beams was investigated. The A0 Lamb wave mode was chosen although the conclusion in this work is also applicable to S0 mode. A Chebyshev pseudospectral Mindlin plate element proposed by authors was employed to simulate the A 0 mode propagation and the interaction of the A0 mode with the delamination. Numerical results show that the sensitivity of A0 mode to the delamination at different frequencies is remarkably different. Each delamination with different lengths or different locations along the through-thickness direction of the laminates generally has at least one or more optimal excitation frequencies which can generate the strongest reflected wave signals from the delamination. The reason for this phenomenon was also investigated by analyzing the natural vibration of the local upper- and lower-delaminated regions. The optimal excitation frequencies were identified to be close to the resonant frequencies of the local delaminated regions with pure flexural vibration modes similar to the deformation pattern of A0 mode.

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Section: Validations Experimental and Numerical Analysis Procedures For Cfrp Beamsmentioning

confidence: 99%

Optimal Excitation Frequency of Lamb Waves for Delamination Detection in CFRP Laminates

Liu

et al. 2009

Journal of Composite Materials

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“…Coherent noise due to spurious signals from reflectors not directly in front or behind the transducer is frequently a more serious problem in practical applications than coherent noise due to other modes. A wedge transducer containing a phased array of piezoelectric elements that enables a guided wave to be focused and steered has been reported [16]. However, this device was still limited to a reasonably small angular range of about 20 • .…”

Section: Introductionmentioning

confidence: 99%

Omni-directional guided wave transducer arrays for the rapid inspection of large areas of plate structures

Wilcox

2003

IEEE Trans. Ultrason., Ferroelect., Freq. Contr.

238

167

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Omni-directional guided wave array transducers contain a circular pattern of elements that individually behave as omni-directional point transmitters or receivers. The data set acquired from such an array contains timedomain signals from each permutation of transmitter and receiver. A phased addition algorithm is developed that allows an omni-directional, B-scan image of the surrounding plate to be synthesized from any geometry of array. Numerically simulated data from a single reflector is used to test the performance of the algorithm. The results from an array containing a fully populated circular area of elements (Type I array) are found to be good, but those from an array containing a single ring of elements (Type II array) contain many large side-lobes. An enhancement to the basic-phased addition algorithm is presented that uses deconvolution to suppress these side-lobes. The deconvolution algorithm enables a Type II array to equal the performance of a Type I array of the same overall diameter. The effect of diameter on angular resolution is investigated. Experimental data obtained from a guided wave array containing electromagnetic acoustic transducers (EMAT) elements for exciting and detecting the S0 Lamb wave mode in a 5-mm thick aluminium plate are processed with both algorithms and the results are discussed.

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“…Scanning the area of interest will provide the image of possible defects. This concept has been used in the detection of surface cracks (Deutsch et al 1997) using self-focussing Lamb waves. In this study, a cross correlation technique was used to determine the time-of-flight differences of signals received by different elements of a sensor array.…”

Section: Introductionmentioning

confidence: 99%

Crack identification based on optimization methods using harmonic elastic waves

Bao

Wang

2009

Int J Fract

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The current paper presents a theoretical study of the identification of cracks in an elastic medium based on optimization methods using harmonic elastic waves. A generalized crack model was used to determine the elastodynamic behaviour of an arbitrarily located and oriented crack subjected to a plane harmonic wave. Sensitivity analysis was conduced to evaluate the variation of stress and strain fields with various crack parameters using the direct differential method (DDM). These general results were then used to identify an unknown crack from known strain components at discrete locations. The BFGS optimization scheme based on the sensitivity analysis was used to determine the length, the orientation and the position of the crack. Numerical simulation was conducted and the results were presented to show the effectiveness of the sensitivity analysis and the optimization method. It was observed that starting from a set of arbitrarily determined initial values, the length, position and the orientation of the crack can be accurately determined.

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Self-Focusing of Rayleigh Waves and Lamb Waves with a Linear Phased Array

Cited by 5 publications

References 0 publications

Optimal Excitation Frequency of Lamb Waves for Delamination Detection in CFRP Laminates

Optimal Excitation Frequency of Lamb Waves for Delamination Detection in CFRP Laminates

Omni-directional guided wave transducer arrays for the rapid inspection of large areas of plate structures

Crack identification based on optimization methods using harmonic elastic waves

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