Effect of the crack length on the piezoelectric damage monitoring of glass fiber epoxy composite DCB specimens

A new nondestructive method using the piezoelectric characteristics of polymer matrix was suggested for the damage monitoring of glass fiber polymer composites, and the feasibility of the use of the method was proven through basic experiments. Heretofore, most studies have focused on basic material properties such as the piezoelectric properties of unidirectional glass fiber epoxy composites with respect to the fiber orientation or the loading speed. In this study, the effect of the crack length on the piezoelectric damage monitoring of glass fiber polymer composites was experimentally investigated. Dynamic tests of mode I were performed using double-cantilever-beam (DCB) specimens, and the relationship between the crack length and the electric-charge signals measured from the electrodes on the DCB specimens was analyzed. The experiment results showed that the magnitude of the electric-charge signals increased very slowly as the crack tip approached the electrodes, rose sharply when the crack tip was passing through the electrodes, and then decreased fast and maintained relatively very low values when the crack tip had completely passed through the electrodes. The investigation of the mechanical behaviors via finite-element analyses during the dynamic tests revealed that the tendency of electric-charge signals is quite similar to that of the strain changes in glass fiber epoxy composites near electrodes. Based on the results of the experiments and finite-element analyses conducted in this study, it was concluded that piezoelectric damage monitoring can detect crack propagation.