In this work, enhanced thermal data processing is developed with experimental procedures, improving visualization algorithm for sub-surface defect detection on industrial composites. These materials are prone to successful infrared nondestructive investigation analyses, since defects are easily characterized by temperature response under thermal pulses with reliable results. Better defect characterization is achieved analyzing data with refined processing and experimental procedures, providing detailed contrasts maps where defects are better distinguished. Thermal data are analyzed for different CFRP specimens with artificial defects and experimental procedures are verified on real structural aeronautical component with internal anomalies due to impact simulation. A better computation method is found to be useful for simultaneous defect detection by means of automatic mapping of absolute contrast, optimized to identify defect boundaries.

In the present work, the results of acoustic nonlinear response of ultrasonic wave propagation when monitoring the progress of damage induced by fatigue on notched C45 carbon steel specimens have been reported. Two ultrasound probes were fixed to the specimens during the tests. The input signal was sinusoidal type, while the corresponding ultrasound response signal was acquired and recorded at each stage of the test by means of a digital oscilloscope. A nonlinear frequency study was performed on the acquired data to evaluate the change in the second- and third-order nonlinearity coefficients of β₁ and β₂, respectively, on the tested specimens. Ultrasonic results were correlated to plastic strain at the notch tip in the initial phases of fatigue and stiffness degradation. The results showed a significant increase in second-order nonlinearity β₁ in the early stages of fatigue life. Subsequently, starting from about 30–40% of the fatigue life, the nonlinearity of β₁ increases. Before final failure, from 80 to 85% of fatigue life, the second-order nonlinearity further increases in the crack propagation stages. The nonlinear parameter of the third-order β₂ was less sensitive to damage than the parameter β₁, showing a rapid increase only starting from approximately 80 to 85% of the fatigue life. The proposed method proved to be valid for detective damage induced by fatigue and to predict the lifetime of metal materials.

The identification of defects in real components made in composite material assumes considerable importance in the aeronautical field, as irregularities in the material can compromise its functionality. Also, the possibility (NDT) to verify the effectiveness of repairing on the component during exercise through non-destructive testing techniques has great importance. The goal of the present study is the application of the ultrasound and thermographic techniques for the identification of defects in a repaired component and the evaluation of the damage caused by the application of cyclical fatigue loads. All the important factors were studied, improving ultrasound scanning and allowing evaluating the effectiveness of the techniques used. In this paper, one case of study was proposed for non-destructive damage evaluation employing Phased Array ultrasonic and thermographic methods on aeronautical CFRP component. The structural element analysed is a spar with a double-T section with a hole and presents a repair by scarfing and hot bond process. The experimental results obtained shown the validity of the ultrasonic and thermographic technique for the sensitivity in detecting defects on full-scale aeronautical components with short execution and scan times.

The work presents a numerical and experimental analysis of a full-scale fatigue test on a CFRP rear spar of an aircraft solicited by a load history representative of variable load levels during the flight conditions. The structural element is essentially a double-T section with a hole and presents a repair by scarfing and hot bond process. The global stress field of the component was determined by a numerical model realized with a commercial FEM code. The numerical model is realized to reproduce the component geometry and stacking sequence, the representative constraints and service loads. The real component has been subjected to cyclic random fatigue stresses and subsequently a static bending load to evaluate the residual strength. Finally, the experimental results obtained, illustrated and discussed, were compared with the numerical ones.