The transition from Lamb waves to longitudinal waves in plates

Abstract

Abstract. We use finite element simulations and experiments to examine the excitation of waves in a plate by normal forces applied to an edge. At low values of the frequency-plate thickness product, f·d, multiple Lamb wave modes are excited with different group velocities, but increasing f·d leads to the formation of a train of well-defined nearly-longitudinal pulses. We investigate the transition between these two wave types, and for the train of nearlylongitudinal pulses we determine the rate at which energy is transferred from the leading pulse to the trailing pulses. Finally, we examine the potential of these longitudinal waves for flaw detection. Experiments and simulations show that the longitudinal pulse train is reflected or transmitted from a slot without significant mode conversion.

High-frequency guided ultrasonic waves to monitor corrosion thickness loss

“…High frequency guided ultrasonic waves allow for the inspection of structures over reasonably long distances [20], and can be employed even if local access to the inspected part is not possible. Depending on the chosen frequency-thickness operating point, wavelengths are comparable to those used in bulk wave ultrasonic testing (UT), giving good sensitivity for small defect detection [12]. Continuing previously reported work for corrosion monitoring in steel structures [20], the superposition of the first anti-symmetric A0 and symmetric S0 Lamb wave modes at about 5 MHz mm (500 kHz excitation frequency in an approximately 10 mm thick steel plate) is investigated here [21].…”

“…The application of guided ultrasonic wave modes in the higher frequency-thickness range has been investigated to obtain better sensitivity for small defects. The S0 mode (around 5 MHz mm) was used for corrosion detection in aircraft structures [11], and longitudinal modes (above 15 MHz mm) were employed for plate inspection [12]. Higher order mode clusters of guided wave modes up to about 20 MHz mm were used to monitor plates [13].…”

Monitoring of corrosion damage using high-frequency guided ultrasonic waves

“…This type of ultrasonic waves allows for the inspection of structures over reasonably long distances, and can be employed even if local access to the inspected part is not possible. The employed wavelengths are comparable to those commonly used in Copper cathode bulk wave ultrasonic testing (UT), possibly allowing good sensitivity for the detection of small defects [12]. The use of high frequency guided waves (coupled Rayleigh-like waves) at around 6.75 MHz mm has been studied for the detection and localization of surface defects in plates [13].…”

Monitoring of corrosion damage using high-frequency guided ultrasonic waves

“…The S 0 mode (around 5 MHz mm) was used for corrosion detection in aircraft structures [11], and longitudinal modes (above 15 MHz mm) were employed for plate inspection [12]. This type of ultrasonic waves allows for the inspection of structures over reasonably long distances, and can be employed even if local access to the inspected part is not possible.…”