Ultrasonic detection and sizing of compressed cracks in glass- and carbon-fibre reinforced plastic composites

Abstract

Non-destructive evaluation of compressed cracks is a major challenge. A quantitative study of the effect of crack-tip closure on the pulse-echo ultrasonic sizing of delaminations in fibre-reinforced polymer-matrix composites (FRP) is presented. In particular, this study focuses on the interaction of ultrasound with a closed crack or kissing disbond, and their effect on the ultrasonic inspectability of FRP laminates consisting of carbon and glass plies. The compression of laminar cracks in these two different laminate types is clearly detectable via both pulse-echo and through-transmission ultrasonic measurements, but the reflected ultrasonic pulses in the two material types exhibit markedly different behaviour. The glass-fibre laminates show a drop in the reflected signal for crack openings up to approximately half the crack growth load, whereas the corresponding carbon-fibre laminates show the expected increase in the reflected signal as the crack opens. The origins of the observed effect of crack closure on the reflection and transmission of ultrasound are analysed in detail to ascertain possible mechanisms responsible for these effects.

Novel Processing Algorithm to Improve Detectability of Disbonds in Adhesive Dissimilar Material Joints

“…The time of signal reflections from the sample boundaries was calculated according to Equation (7). Aluminum side inspection was selected, since CFRP is a more attenuating material due to its material characteristic and laminate structure [44]. However, the thickness of the aluminum layer is quite thin, which can lead to the overlapping of different signal reflections [8,35,36].…”

A Nonlinear Method for Characterizing Discrete Defects in Thick Multilayer Composites

“…The most commonly used threshold is that with a fixed value. In order to find the statistical behavior of the RQA parameters, while both the DET and LAM are variables that are based on the total amount of recurrence points according to Equations (4) and (5), the recurrence point rate RR needs to be determined first. Usually, RR takes 0.1; the threshold should be adjusted so that the statistical mean of RRs of all signals is 0.1.…”

“…Li et al [4] used the ultrasonic arrays technique to improve the characterization of side drilled holes in a 19 mm thick CFRP block, in which the holes were 1.5 mm in diameter and 16 mm in length and down to a depth of 16 mm. Ibrahim et al [5] performed single-sided technique of contact pulse-echo inspection on CFRP specimen with thickness of 10 mm, to study the effect of crack in the middle of the specimen, while the length of the crack is approximately 25 mm. Smith et al [6] have successfully applied a two-dimensional fast Fourier transform (2D-FFT) method to B-scan images for detecting out of plane fiber waviness in structures that are as thick as 18 mm.…”

Inspection of Dissimilar Material Joints Using Ultrasonic Phased Arrays

“…Therefore, the value of amplitudes of reflected signal can be very low so it can be complicated to detect delaminations. Higher ultrasound velocity in steel layer was taken into account as well [5], [7]. The sample is inspected from metal side using one probe as emitter and receiver of ultrasound signal.…”

“…Ultrasonic non-destructive inspection techniques are widely used for evaluation of quality of joints of different materials [3]- [7]. However, there are limited studies in the field of the inspection of metal-composite adhesive joints using ultrasonic techniques.…”