Laser Optoacoustic Method for Quantitative Porosity Assessment of Carbon Fiber Reinforced Plastic Composites Based on Acoustic Impedance Measurement

Abstract

Abstract—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.