Advanced ultrasonic non-destructive testing for damage detection on thick and curved composite elements for constructions

Abstract

In this work, the problem of non-destructive testing on composite components with complex shapes for civil constructions and transport infrastructures is analyzed. In such applications at the state of the art main challenges are related with the inspection of thick sandwiches with low density cores (below 80 kg/m3) and curved panels. After a review of suitable non-destructive testing techniques, an original set-up for low frequency (100 kHz) ultrasonic inspection is proposed, which combines different solutions in through-transmission mode. The set-up is based on a hybrid configuration coupling a contact emitting probe with a non-contact air-coupled receiver. The use of a contact probe in emission is necessary to have enough energy to analyze thick components with low density core. The contact between probe and surface is made small (spot of 1 mm) and smooth using a spherical cap to increase lateral resolution at low frequency and to allow scan on irregular surfaces sometimes present in curved parts. To improve understanding this cap has been tested here also with a single probe in pulse echo mode. The non-contact probe in reception allows a better inspection flexibility on curved and thick components, where pulse echo is not feasible at all. The system is mainly developed for inspection after production in an industrialized production process, where through-transmission testing is possible. The analysis of results on two different samples (one thick sandwich with low density 40 kg/m3, 50 mm thick PUR core and one curved laminate panel) shows that the proposed methods can efficiently inspect construction composites of complex shape with satisfactory signal-to-noise ratio (usually SNR > 15 dB) and lateral resolution (2–3 mm).

Reliability analysis of laser ultrasonics for train axle diagnostics based on model assisted POD curves

“…The technique analyzed in this paper is the laser ultrasonics which is based on high energy pulsed laser for generation of ultrasonic waves and then air coupled ultrasonic probe for detecting the waves, as recently presented by the authors in [5]. Air-coupled ultrasonic probes are non-contact in nature and has already been used in many industrial and civil applications [8][9] [10], however also Laser Doppler Vibrometry can be used for detection. These non-contact methods can facilitate the inspection of hard-to-reach areas with respect to contact ultrasonic probe methods, which need some medium like couplant for effective transmission of ultrasonic waves.…”

Experimental investigation by laser ultrasonics for high speed train axle diagnostics

“…Air-coupled ultrasound inspection has already been successfully used in many industrial applications e.g. NDT on both thick [6] and thin [7] composites, NDT on light thin historical vaults [8], density measurement of ceramic tiles [9], wood detection [10], and thin metallic laminated [11,12]. http://dx.doi.org/10.1016/j.ultras.2014.08.010 0041-624X/Ó 2014 Elsevier B.V. All rights reserved.…”

Air-Coupled Ultrasound Time Reversal (ACU-TR) For Subwavelength Nondestructive Imaging

“…However, this limits the lateral defect resolution to the size of the transducer elements [18]- [22].…”