Damage signature of fatigued fabric reinforced plastics in the pulsed ultrasonic polar scan

This study investigates the use of both the amplitude and time-of-flight based pulsed ultrasonic polar scan (P-UPS) for the nondestructive detection and evaluation of fatigue damage in fiber reinforced composites. Several thermoplastic carbon fabric reinforced PPS specimens (CETEX), loaded under various fatigue conditions, have been scanned at multiple material spots according to the P-UPS technique in order to extract material degradation in a quantitative way. The P-UPS results indicate that shear dominated fatigued carbon/PPS goes with a reduction of shear properties combined with large fiber distortions. The P-UPS results of the tension-tension fatigued carbon/PPS samples on the other hand reveal a directional degradation of the stiffness properties, reaching a maximum reduction of -12.8% along the loading direction. The P-UPS extracted damage characteristics are fully supported by simulations, conventional destructive tests as well as visual inspection. The results demonstrate the excellent capability of the P-UPS method for nondestructively assessing and quantifying both shear-dominated and tension-tension fatigue damage in fabric reinforced plastics

Treatment of Attenuation and Dispersion in the Propagation of Ultrasonic Pulses

Computer simulation techniques are continuously expanding their role as basic tools in fields, such as Quantitative Non Destructive Evaluation, in which it is important to gain a good understanding of the propagation mechanisms of waves or pulses in complex media. A method, which has been designed for the above purpose and is particularly efficient, especially if applied in conjunction with parallel processing, is the Local Interaction Simulation Approach (LISA)[l–3]. As spin-offs of LISA, the Sharp Interface Model (SIM)[4] and the Spring Model have overcome [5] the difficulties encountered in treating sharp or imperfect contact interfaces by means of the usual Finite Difference (FD) techniques

Discrimination Between Cracks and Recrystallization in Steel Using Nonlinear Techniques

One major problem in ultrasonic NDT for steel products and welding inspection is that standard linear methods are often unable to distinguish the nature of signals. Partially recrystallized grains, voids, small cracks or inclusions in the piece under investigation could produce indications very similar in terms of acoustic energy reflected and ultrasonic peaks envelope. Here, we analyze the nonlinear response to ultrasonic excitations of steel bars with both kind of imperfections purposefully generated. Using the Scaling Subtraction Method as a tool for the analysis, we show differences in the nonlinear signature, which can be used to distinguish nondestructively a crack/delamination from a region with imperfect grains formation, with possible applications of this technique in the production cycl