Application of Laser-Ultrasonic Technique of Acoustic Impedance Measurement with Signals Detection by Backward-Mode Sche
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Application of Laser‑Ultrasonic Technique of Acoustic Impedance Measurement with Signals Detection by Backward‑Mode Scheme for Porosity Content Evaluation in CFRP Laminates Yu. G. Sokolovskaya1 · N. B. Podymova1 · A. A. Karabutov2,3 Received: 29 February 2020 / Accepted: 22 June 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract The aim of this work is the development and experimental implementation of the laser-ultrasonic method for CFRPs porosity assessment with one-side access to an investigated object. The scheme with the laser thermooptical generation and backwardmode piezoelectric detection of longitudinal acoustic waves is used. The proposed method is based on the measurement of the acoustic impedance of a composite specimen by using the value of the integral of the ultrasonic pulse reflected from an immersion layer-specimen interface. The existence of the relationship between the porosity content, ultrasound velocity, and material’s density allows one to assess the porosity of CFRPs by the measured acoustic impedance. The proposed method does not require plane parallelism of the input and output surfaces of the studied objects, as well as measuring the thickness of the object. This allows studying CFRP structures with complex shapes. This method may be of use for various types of composite materials, regardless of acoustical waves propagating features related to a periodical material’s structure. CFRP specimens with three reinforcement schemes and different average volume porosity contents were investigated. It is shown that the local porosity distribution in the studied CFRPs is nonuniform along the fiber stacking plane. The porosity content obtained by the laser-ultrasonic method was checked using the X-ray computer tomography. The porosity values, averaged from the laser-ultrasonic measurement results, coincide with the X-ray tomography data within the error limits. The method can be useful for quality control of obtained composite structures with the aim of modernization of technology processes and selecting optimal production conditions and also for the detection of changes in composite structures during their operation or during fatigue testing processes. Keywords CFRP · Polymer composites · Porosity · Laser ultrasonics · Longitudinal acoustic waves
1 Introduction Polymer composite materials are currently widely used in industry [1]. One example of such materials is carbon fiber reinforced plastic (CFRP) composites based on carbon fibers and organic matrix. The use of carbon fiber reinforcement in combination with polymer matrix allows one to obtain a * Yu. G. Sokolovskaya [email protected] 1
Department of Physics, M. V. Lomonosov Moscow State University, Moscow, Russia 119991
2
International Laser Center, M. V. Lomonosov Moscow State University, Moscow, Russia 119991
3
The National University of Science and Technology “MISiS”, Leninskii prospect 4, Moscow, Russia 119991
material whose specific physical and mechanical characteristics are higher
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