Abstract
One of the challenging problems in non-destructive evaluation is related to identification and sizing of flaws. A high resolution image of the scanned part is required. This allows, through using adequate post-processing of data, to perform localisation and sizing of a flaw. Several techniques have been introduced recently for this purpose. These include among others the synthetic aperture focusing technique, inverse wave-field extrapolation and the total focusing method. However, large uncertainties are affecting the inverse problem solution as provided by these methods when dealing with small defects. It was recognized that reconstruction based on the ultrasonic synthetic aperture focusing technique elaborated in frequency domain provides high resolution imaging even at large distances. This work focused on this promising procedure for the special case of ultrasonic imaging of flaws in 2D elastic medium under plane strain conditions, where the image is provided by a B-scan. Robustness of detection was investigated through perturbing the radargram by white noise and assessed as function of noise energy. It was found that synthetic aperture focusing technique is insensitive to noise.
Highlights
Flaws in parts can be produced during the manufacturing process or in service due to fatigue or induced accidental damage
Ultrasonic testing can be used for this purpose [1,2]. This may be performed by means of ultrasonic imaging which involves converting raw ultrasonic data collected by a transducer during a B-scan testing into an image representing with sufficient precision the interior state of the examined structure
The concept of synthetic aperture appeared at first in the field of radar in 1951 when the technique of synthetic aperture radar (SAR) imaging was introduced [4]. This approach is based on a combination of measurements taken by moving radar to synthesize electromagnetic signals with a better resolution than that provided by fixed radar
Summary
Flaws in parts can be produced during the manufacturing process or in service due to fatigue or induced accidental damage. Ultrasonic testing can be used for this purpose [1,2] This may be performed by means of ultrasonic imaging which involves converting raw ultrasonic data collected by a transducer during a B-scan testing into an image representing with sufficient precision the interior state of the examined structure. This conversion can be achieved by the synthetic aperture focusing technique [3]. In the 1970s, the synthetic aperture focusing reached the field of ultrasonics and his name became aperture focusing technique (SAFT) [7] This flexible imaging method was firstly explored for non-destructive testing using ultrasonic transducers to inspect an isotropic medium. SAFT algorithm was used after that for reconstruction of defects in anisotropic media [8,9] where wave propagation is more complex because of the directional dependence of the material properties
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