Quantitative analysis of the influence of voids and delaminations on acoustic attenuation in CFRP composites by the laser-ultrasonic spectroscopy method (original) (raw)
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2014
This work aims at applying the method of broadband laser-ultrasonic s pectroscopy for quantitative evaluation of the effect of isolated dispersed voids and extended interply delaminations o n the acoustic attenuation and on the phase velocity in CFRP composite laminates. The specimens have differen t total porosity levels up to 10.5% determined by the X-ray computer tomography. The ultrasonic attenuation resonan ce and the corresponding jump of the phase velocity are observed in all specimens governed by th eir periodic layered structure. The absolute maximum and the frequency bandwidth of the resonance atten uation peak, as well as the low-frequency velocity dispersion depend on the total porosity level formed by the pr edominant imperfections in the composite structure, either isolated microscopic dispersed spheroidal voids or extended in terply delaminations.
Journal of Nondestructive Evaluation, 2013
The laser-ultrasonic method for nondestructive quantitative local porosity assessment for CFRP composites is proposed and realized experimentally for only one available flat surface of a specimen or a product. This method combines the laser thermoelastic generation and the highsensitivity piezoelectric detection of broadband pulses of longitudinal ultrasonic waves and does not require the detection of the backwall echo ultrasonic signal. The generation and the detection of ultrasonic pulses is carried out with the specially designed laser-ultrasonic transducer, which allows one to obtain both the temporal profile and the frequency spectrum of a part of the ultrasonic signal backscattered by gas voids in a composite specimen. The frequency spectrum of backscattered ultrasonic pulses is analyzed for three sets of CFRP specimens with different epoxy matrix fractions and porosity. The empirical relation between porosity of CFRP specimens and the spectral power (structural noise power) of ultrasonic signals backscattered by voids is obtained for porosity values up to 0.15. This relation allows one to evaluate the local porosity from measured structural noise power both for CFRP specimens and products fabricated from the same composite material. The proposed laser-ultrasonic setup demonstrates a basis for a system of CFRP porosity assessment in field conditions. It can be very useful especially for nondestructive detection of structural changes of composite materials that will allow evaluation of products during their life time.
Detection of delamination defects in CFRP materials using ultrasonic signal processing
Ultrasonics, 2008
In this paper, signal processing techniques are tested for their ability to resolve echoes associated with delaminations in carbon fiberreinforced polymer multi-layered composite materials (CFRP) detected by ultrasonic methods. These methods include split spectrum processing (SSP) and the expectation-maximization (EM) algorithm. A simulation study on defect detection was performed, and results were validated experimentally on CFRP with and without delamination defects taken from aircraft. Comparison of the methods for their ability to resolve echoes are made.
Finite element analysis of ultrasonic CFRP laminate inspection
2016
Carbon Fibre Reinforced Polymer (CFRP) materials pose a challenge for NDE inspections due to their anisotropic material properties and often complex morphologies. Simulation is a vital tool in the design of ultrasonic inspections, improving setup and helping understand wave propagation in complex components. In this work, three different approaches of constructing accurate Finite Element Analysis (FEA) models of CFRP components are presented. The first approach generates a model of a flat CFRP laminate using the design specification to construct the idealised laminate geometry – essentially recreating the ‘as designed’ component in the model. The second approach utilises photomicrographs of the laminates’ cross-section to produce a more realistic ‘as built’ geometry within the model. Ultrasonic inspection simulations performed show a good correlation when comparing resulting A-scans with experiments. A final modelling approach of using an image of X-Ray CT data is then performed to ...
Ultrasonic Attenuation of Carbon-Fiber Reinforced Composites
Journal of Composites Science
Ultrasonic attenuation measurements were conducted on cross-ply and quasi-isotropic lay-ups of eight types of carbon-fiber reinforced composites (CFRPs) using through-transmission methods with diffraction correction. Attenuation values were substantially higher than those of unidirectional composites and other structural materials. Wave modes, fiber distributions, matrix resins, and consolidation methods affected total attenuation. Transverse mode, quasi-isotropic lay-up, and polyimide and thermoplastic resins generally produced higher attenuation. No clear trends from the fiber distribution were revealed, indicating that it is not feasible presently to predict the attenuation of various lay-ups from the unidirectional values. That is, direct attenuation tests for different laminate lay-ups are needed. This work expanded the existing attenuation database by properly determining the attenuation coefficients of two additional layup types of CFRP laminates. Results showed the merit of ...
Air-Coupled Ultrasonic C-scan Effectiveness for Impact Damage Evaluation in CFRP Laminates
This study aimed to evaluate the effectiveness of using air-coupled ultrasonic C-scan to assess the impact damage in laminates. The air-coupled C-scan was experimentally tested in Carbon Fibre Reinforced Plastics (CFRP) as the ones with high practical concern and also due to its higher sensitivity to damage than other composite materials. Four laminate types were used with different stacking sequences: [0 2 ,90 2 ] S , [0 3 ,90 3 ] S , [0 4 ,90 4 ] S and [0 5 ,90 5 ] S and thicknesses of 1.2, 1.8, 2.4 and 3.0 mm, respectively. Multiple impact were also carried out and analysed. Quality control of the plates was performed by immersion C-Scan using 20 MHz transducers in through-transmission mode to evaluate the eventual presence of defects resulting from the manufacturing process, and also to assess the impact damages. The results are very similar comparing the size and shape of defects. However, damage depth evaluation by air-coupled C-Scan is not possible.
Quantitative Evaluation of Porosity in Unidirectional CFRPs Using Laser Ultrasonic Method
Russian Journal of Nondestructive Testing, 2020
A method for estimating the porosity of CFRPs based on measuring their acoustic impedances is proposed and experimentally implemented. The acoustic impedance of the test sample is derived from the magnitude of the antiderivative of an ultrasonic pulse reflected from the immersionliquid-sample interface. The studied samples are unidirectional CFRPs with various volume contents of the matrix and filler. It has been established that the distribution of local porosity in the samples is uneven along the carbon fiber stacking plane. The value of porosity averaged over the results of optical-acoustic measurements with allowance for measurement errors is consistent with the X-ray tomography data. The method for estimating the value of porosity presented in this paper does not involve measuring the volume and mass of the object under study and can be used in diagnostics of complex shaped composite structures.
Acoustical Physics, 2020
A method for measuring the acoustic impedance for the assessment of the porosity of carbon fiber reinforced plastic composites using laser thermo-optical excitation of longitudinal acoustic waves is proposed and experimentally realized. The acoustic impedance of the test sample is measured from the magnitude of the antiderivative ultrasonic pulse reflected from the immersion liquid-sample interface. A method for calculating the porosity of carbon fiber plastic composites based on the measured acoustic impedance is presented. Composite samples with three different carbon fiber layers stacking schemes were investigated. It is shown that in the studied composites, the local porosity distribution is nonuniform along the fiber stacking plane. The porosity value, averaged from optoacoustic measurement results, actually coincides with X-ray tomography data within the error limits. The presented method for determining porosity does not require determining the volume and mass of the studied object and can be used for investigation of composite structures with complex shapes.