Development of a System for Detecting Weld Failures

Development of a System for Detecting Weld Failures

Jairo Alejandro Rodríguez (Universidad Santo Tomás, Colombia) and Edwin F. Forero (Universidad Santo Tomás, Colombia)
Copyright: © 2015 |Pages: 17
DOI: 10.4018/978-1-4666-8490-4.ch004
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Abstract

Considering the possibility that from the area of electronics can be provided feasible solutions in the field of non-destructive testing, this chapter present a prototype and methodology that allows energize an ultrasound transducer. This system is used to evaluate for detecting weld failures at the junctions of metallic parts. Subsequently, in order to validate the design quality of that source, a computer system that allows control of a card developed ultrasound. Finally, it is implemented the ultrasonic imaging by time of flight diffraction technique, in order to obtain an objective comparison methodology to both systems.
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Fundamentals Of Ultrasound

The sound generated beyond 20,000 Hz is called ultrasound, but the frequency range used in nondestructive testing ranges from 100000 Hz to 50 MHz, and like any sound wave meets the physical properties of sound, but differs in the short wavelength, because it can interact with small particles, such as discontinuities eventually in welded joints regions. Considering that the wavelength is inversely proportional to frequency, it follows that to achieve short wavelengths it is necessary that the disturbance in a particular environment often vibrate every second.

(1)

It is known that the human ear, on average, is capable of capturing vibrations between 20 and 20000 Hz, as it cannot perceive the range below 20 Hz and above 20,000 Hz, infrasound and ultrasound regions, respectively. See Figure 1.

Figure 1.

Representation of the sound spectrum

Among the physical properties that obey ultrasound, are the reflection, scattering, refraction and diffraction, all of them are very useful in non-destructive testing with ultrasound. As is known, the light is also a wave disturbance, but there is a notable difference between light waves and sound waves. While light can propagate in a vacuum, sound cannot do it; ie, the sound needs a medium to be spread, whether it is fluid or solid.

The sound propagates in fluid media as a longitudinal disturbance; this means that the traveling direction is parallel to vibration the medium through which it propagates. However, in solid media, the sound is propagated as a longitudinal wave and as transverse cutting wave, which means that the molecules vibrate perpendicularly to the direction of sound propagation. Also, exist Rayleigh waves; these have an elliptical vibration surface, and Lamb, which are disturbances whose wavelength is greater than the thickness of the solid through which they propagate (Charlesworth, J. P. 2001).

Considering a longitudinal transmission of a sound wave when moving by a certain medium, which occurs are spatial variations in time due to the compression and expansion of the molecules making up said means to measure the pressure wave propagates. See Figure 2.

Figure 2.

Illustration of the concept of longitudinal wave, and the physical meaning places for which the wave amplitude takes the maximum and minimum values

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