The revision of inclined crack based on impact-echo spectral tomography
Date Issued
2012
Date
2012
Author(s)
Hsu, Chia-Wen
Abstract
Impact echo method can effectively detect internal defects of concrete, this method is to impact the structure surface to stimulate the stress wave, and then to measure the surface displacement of the Fourier transform, and then interpreted by the peak value of the spectrum of frequencies of defect sites.
When using Impact echo method to detect tilt interface, the specimen surface and the reflection interface is not parallel, so force wave between the two interfaces coming back reflection is not like the rule between two parallel surfaces.
Therefore, spectrum echo peak is not necessarily correspond to the measuring point just below the interface, and the echo frequency peak is not too obvious.If you use the image method to draw a spectral tomography, you will find out the inclination and position of the interface have a slight deviation.
The purpose of this study is to develop an effective Spectral Tomography Tilt Interface Amendment Method to amend mutual interference cause by the stress wave returns from tilt interface . This paper presents a Spectral Migration Image Method, similar to the Earth’s Interior Migration Method, but the signal processing is not a time domain signal, but the frequency domain signal.
Migration uses the oval superposition principle, the energy of each frequency in the spectrum of all measured points spread to the entire semi-elliptical, each pixel from all points of the energy overlay.
As the Spectral Migration Image Method, frequency amplitude spectrum of each pixel of the image have the same proportion of the contribution will result in non-tilt interface location of the Interference signal. This article re-use of the method of weight distribution to enhance the tilt interface reflection energy and remove the image correction resulting from the Interference signal.
In addition, the gradation conversion of spectrum images to enhance image contrast. By this paper, the method can make the vertical cross-section image clearly shows the shape and position of the inclined cracks.
This study use the Finite Element Method to simulate six different slope of the inclined cracks, then use numerical results verify the feasibility of the proposed method.
From numerical simulation results, we can see that through the Spectrum Migration Amendment Method can fix tilt crack location, enhance the signal strength of the crack area and focus on the correct thickness of the defect, and eliminate Interference signal, solve the problem of error in judgment.
This study sets three model tests at the same, the experimental results can also be found that the amendment method proposed in this article can be effectively applied to the experimental signal, accurately identified the location and size of the inclined cracks.
Subjects
impact echo
inclined crack
migration
weighted
spectral tomography
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-101-R99543004-1.pdf
Size
23.54 KB
Format
Adobe PDF
Checksum
(MD5):9ae36718bd6384fca17dc427a6b2547f