Identifying delamination in carbon fiber composites based on defect modes in imperfect phononic crystals

Abstract

Delamination is one of the most common types of damage in fiber-reinforced composites. In this paper, borrowing from the concept of defect modes in imperfect phononic crystals, we propose a method for identifying delamination damages in composite materials. Specifically, by periodically arranging concentrated masses on the surface of a finite carbon fiber beam, the carbon fiber beam becomes a phononic crystal, and defect modes in Bragg bandgaps can be observed when there is delamination. With the spectral element method formulation, we show that the frequencies of defect modes are directly related to the length and location of the delamination. By performing algebraic addition and subtraction on the generated defect mode frequencies when applying excitations at the two ends of a defected carbon fiber composite beam, an approximately linear correlation with the length and location of delamination can be obtained. Our analytical and experimental results indicate that, by introducing periodicity on the carbon fiber composite beam and applying appropriate post-processing algorithm to the generated defect modes, rapid and accurate identification of the delamination length and location can be achieved based on the bandgap characteristics of the imperfect phononic crystals.