Air-coupled ultrasonic through-transmission thickness measurements of steel plates

作者：Waag Grunde^*; Hoff Lars; Norli Petter

来源：Ultrasonics, 2015, 56: 332-339.

DOI：10.1016/j.ultras.2014.08.021

• Air-coupled ultrasound
• Non-destructive testing
• Metals
• Through-transmission
• Angular spectrum method

Non-destructive ultrasonic testing of steel structures provide valuable information in e.g. inspection of pipes, ships and offshore structures. In many practical applications, contact measurements are cumbersome or not possible, and air-coupled ultrasound can provide a solution.
This paper presents air-coupled ultrasonic through-transmission measurements on a steel plate with thicknesses 10.15 mm; 10.0 mm; 9.8 mm. Ultrasound pulses were transmitted from a piezoelectric transducer at normal incidence, through the steel plate, and were received at the opposite side. The S(1,)A(2) and A(3) modes of the plate are excited, with resonance frequencies that depend on the material properties and the thickness of the plate.
The results show that the resonances could be clearly identified after transmission through the steel plate, and that the frequencies of the resonances could be used to distinguish between the three plate thicknesses.
The S-1-mode resonance was observed to be shifted 10% down compared to a simple plane wave half-wave resonance model, while the A(2) and S-2 modes were found approximately at the corresponding plane-wave resonance frequencies.
A model based on the angular spectrum method was used to predict the response of the through-transmission setup. This model included the finite aperture of the transmitter and receiver, and compressional and shear waves in the solid. The model predicts the frequencies of the observed modes of the plate to within 1%, including the down-shift of the S-1-mode.

• 出版日期2015-2