Nondestructive Methods

This chapter contains fundamentals of physics related to nondestructive evaluation (NDE), nondestructive testing (NDT), nondestructive inspection (NDI) or nondestructive examination (NDE) of structural components using ultrasonic waves, ultrasonic thermography (UT), radiography, magnetic particle, eddy currents, and dye penetrant or liquid penetrant. In essence, sound waves are vibrations carrying vibrational energy that is transmitted through a medium and are classified as pleasant sound (speech, music, sound of birds, etc.) or unpleasant audible waves (noise). On the other hand, ultrasonic waves are high-frequency vibrations and are inaudible sound waves to humans. Commonly, audible sound waves propagate in space having a frequency (f) range related to the speed of sound in decibels (dB) units. Specifically, the frequency range of human hearing (audible range of sound) is \(20\,Hz < f < 20--03\,Hz\) , which is converted to \(0\,dB < Lp < 140\,dB\) at ambient temperature. The extreme values represent the threshold of hearing and the threshold of pain, respectively. Conversely, non-audible sound waves are treated as ultrasonic waves that are suitable for quality control inspection.