Variance Based Method for Signal Separation in Ultrasonic Non-Destructive Testing
Abhilash Jose M V1, Aparna P R2

1Abhilash Jose M V, Department of Electronics and Communication, SCT College of Engineering, Trivandrum (Kerala), India.
2Aparna P R, Department of Electronics and Communication, SCT College of Engineering, Trivandrum (Kerala), India.

Manuscript received on 13 June 2017 | Revised Manuscript received on 20 June 2017 | Manuscript Published on 30 June 2017 | PP: 316-321 | Volume-6 Issue-5, June 2017 | Retrieval Number: E5095066517/17©BEIESP
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Abstract: This paper proposes a variance based method for ultrasonic defect detection for non-destructive testing of maraging steel. Maraging steel is a carbon free iron-nickel alloy which has superior strength and toughness. It also has a high malleability making possible for it to be easily machined and welded. Maraging steels are used extensively in the space industry for the construction of rocket motor casings, owing to its greater strength and fracture toughness. During its fabrication, defects like cracks may develop in the maraging steel. The cracks have a tendency to grow and spread, eventually leading to the fracture of the material. Non-destructive testing methods like ultrasound testing are used for the regular inspection of maraging steel rocket motor cases. Improving the probability of detection is a demanding task since the space industry has a very rigorous acceptance criteria and the permissibility of defects is very small. The sensitivity and resolution of ultrasonic systems is greatly reduced by the noise in the acquired ultrasound signals produced due to the coarse and textured microstructure of maraging steel. The main goal here is to successfully detect the defect signal hidden in the noise. Defects of a large size may be easier to detect, but the difficulty arises in the case of smaller defects which produces ultrasonic echoes whose amplitude is similar to that of the material noise. Successful detection of these smaller defects is essential for the space vehicle to achieve its designed payload capacity. The method presented here calculates and compares the variance of the acquired ultrasound signals, for separating the defect signal from noise. Further improvement in the detection can be achieved by comparing variance of Fourier transform coefficients of the acquired signals.
Keywords: Maraging Steel, Non-Destructive Testing, Ultrasound, Fast Fourier Transform, QUT 2003, Variance.

Scope of the Article: Signal and Speech Processing