In-situ structural health monitoring of glass fiber reinforced composites by tufted reinforcement

Through-the-thickness reinforcement (TTR) techniques have been increasingly applied to fiber-reinforced polymer composite laminates to reduce the issues caused by the weak out-of-plane properties which can reduce significantly their load-bearing capacity. The present work investigates the electrical response of carbon tuft threads as reinforcements of GFRP omega stiffened panel. Besides the mechanical contribution of the tuft reinforcements to the composites structures, this study focuses on the evaluation of the electrical response on the tufted yarns as a means of monitor the structural health. The first studies consisted of evaluating GFRP composite laminate plates reinforced with carbon tufts by means of the electrical response through tufts to damage generated by multiple low-velocity impacts. Once the tufts exhibited their ability to respond continuously while increasing damage, pull-off mechanical tests were performed in the omega stiffeners assisted by electrical resistance measurements as well as acoustic emission (AE) and Digital Image Correlation (DIC). The results showed that the measures of electric resistance on the yarns are capable to distinguish important events during the mechanical tests, as the delamination and tuft failure. Furthermore, they are in common agreement with the cumulative energy on AE and strain field response on DIC. (paper)