Nonlinear Ultrasonic Imaging for Porosity Evaluation

Abstract

The influence of porosity on the mechanical behaviour of composite laminates represents a complex problem that involves many variables. Therefore, the evaluation of the type and volume content of porosity in a composite specimen is important for quality control and for predicting material behaviour during service. A suitable way to evaluate the porosity content in composites is by using nonlinear ultrasonics because of their sensitivity to small cracks. The main objective of this research work is to present an imaging method for the porosity field in composites. Two nonlinear ultrasound techniques are proposed using backscattered signals acquired by a phased array system. The first method was based on the amplitude of the half-harmonic frequency components generated by microbubble reflections, while the second one involved the frequency derivative of the attenuation coefficient, which is proportional to the porosity content in the specimen. Two composite samples with induced porosity were considered in the experimental tests, and the results showed the high accuracy of both methods with respect to a classic C-scan baseline. The attenuation coefficient results showed high accuracy in defining bubble shapes in comparison with the half-harmonic technique when surface effects were neglected.

Research on the 3D Reverse Time Migration Technique for Internal Defects Imaging and Sensor Settings of Pressure Pipelines

“…Its merits include high sensitivity, compact equipment, and a non-invasive nature that poses no risks to both human health and environmental quality [13]. UT can proficiently ascertain flaw dimensions, identify crack locations [14], delamination location, and determine the stacking sequence of composites [15][16][17] through the propagation of surface waves, guided waves, and body waves [18,19]. Subsequently, employing ultrasonic imaging methods allows for the intuitive visualization of defects within pressure pipelines [20][21][22].…”