How ultrasonic waves are used to detect defect in components?
Answers
Ultrasonic testing (UT) is an acoustic inspection technique measuring reflection or transmission of pulsed elastic waves in engineering materials.
Ultrasonic testing is used to find internal defects within a weld or body of a component being tested. A probe emits a sound wave that is passed through the material.
Ultrasonic testing has the capability of allowing the visualization of defects within the structure and providing estimates of the physical properties of the components (Brown and Lebowitz, 1994). Measurement of ultrasonic phase velocity and attenuation are directly related to the bulk and shear modulus and Poisson's ratio of the material. Certain materials, such as glass reinforced plastic composites (GRPC), are highly attenuating and measurements are consequently very difficult to make. Metals are more conducive to study and have been extensively investigated. Acoustic methods and related vibration methods such as ultrasonic, acoustic impedance, free oscillation, shear wave methods, reverberation, and acoustic emission are widely used (Lange, 1975, 1976; Lange and Moskovenko, 1978). Not all NDE methods used for metals can be used for composites. The sensitivity of methods for the detection of flaws in composites is one-third to one-quarter of that for steel. High-frequency ultrasonic methods are ineffective for the inspection of polymer composites because of strong scattering and damping above 1 MHz. Acoustic NDE equipment employs ultrasound with frequencies in the range of 50 Hz to 50 MHz. The intensity of the oscillations is usually less than 1 W cm−2. Acoustic methods are divided into two groups depending on the method of generation and detection of the waves. Active methods use the generation and detection of acoustic waves, whereas the passive methods only detect emitted acoustic signals. In each group, methods distinguish between longitudinal, shear, and standing waves.