Ply-orientation measurements in composites using structure-tensor analysis of volumetric ultrasonic data

Abstract

Ply wrinkling in carbon fibre reinforced polymer (CFRP) laminates is often geometrically complex and difficult to quantify using non-destructive techniques. In this paper, an ultrasonic technique for mapping ply wrinkling is presented. The instantaneous-phase three-dimensional dataset obtained from a pulse-echo ultrasonic inspection is processed using the structure-tensor image processing technique to quantify the orientations of the internal plies of a CFRP laminate. It is shown that consideration must be given to the wrapped nature of the phase dataset during processing to obtain accurate orientation maps. Three dimensional ply orientation and ply-location maps obtained from a test coupon are compared with true ply angles and locations by overlaying the ultrasonically-derived results on X-ray CT image slices, showing that accurate orientation maps can be obtained using the proposed technique.

Fibre direction and stacking sequence measurement in carbon fibre composites using Radon transforms of ultrasonic data

“…Many techniques for detecting fibres and measuring their orientation are seen in the literature [9], spanning many scientific fields. Examples include techniques based on structure tensor [22][23][24][25][26][27][28], Radon transform [29][30][31][32], Fast Fourier Transform (FFT) [14,[33][34][35][36][37][38], rotated filter [39][40][41][42][43][44], and image moment [45][46][47] methods.…”

“…Whilst the structure tensor has been previously used by the authors to successfully determine out-of-plane ply orientation from ultrasonic data [22], it is not an appropriate method for in-plane fibre orientation. Unlike the smoothly varying ply-orientation field, the fibre-orientation field is likely to feature abrupt changes each side of a resin layer, for example switching from a −45°to a +45°fibre angle.…”

Wrinkle measurement in glass-carbon hybrid laminates comparing ultrasonic techniques: A case study

“…In general, the intention is to measure the full-thickness ultrasonic attenuation and to detect any defects that reflect ultrasound. For characterising wrinkles, a focused probe with a focal depth set at the mid-plane of the material has been shown to be optimal (17) . Whilst the phased-array and FMC/TFM methods using linear arrays were only cylindrically focusing (in one plane), the single-element probe has a spherical focus and this may offer some advantages, although the anisotropy of the material may make this a disadvantage.…”

“…Ultrasonic techniques providing an acceptable detail level for 3D characterisation of fibre orientation can be used on large components and allow the inspection of both glass and carbon fibre. The ply lay-up of composite materials can be imaged through the 3D ultrasonic full-waveform scans of the samples (15)(16)(17) . However, unlike Micro-CT, the raw datasets from an ultrasonic inspection do not automatically reveal the ply lay-up using the common 'gate' method of signal analysis.…”

“…Current research shows how the depths of the resin layers can be tracked using the instantaneous amplitude, phase and frequency of the ultrasonic response in 3D scans, allowing out-of-plane wrinkles to be mapped within the structure (18)(19) . These instantaneous parameters are defined via the following equation for the analytic signal (17) : (1) where A(t) is the instantaneous amplitude and ϕ(t) is the instantaneous phase at time t. The imaginary part of the analytic signal is calculated by applying a Hilbert transform to the measured (real) waveform (20) . The instantaneous frequency, f(t) is the rate of change of phase at time t in the response at the measurement location and is given (21)…”