Damage identification of prepreg composites subject to accelerated fatigue tests

The fatigue behavior of composite materials under time-dependent loading is investigated. Fatigue is induced in test beams using an electro-magnetic shaker. The test beams made of prepreg composite materials with a layup [(±45)2]S before and after fatigue loading are used as a case study for the proposed method. The averaged stiffness properties of the test specimen are monitored during the fatigue cycles by measuring the first natural frequency. The first bending mode shapes of the test beams are measured using a laser scanning vibrometer at selected fatigue stages. Based on this modal information, the (reduced) bending stiffness distribution of the test beam is identified using an inverse method

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