Polarization-resolved terahertz imaging of intra- and inter-laminar damages in hybrid fiber-reinforced composite laminate subject to low-velocity impact

Terahertz imaging is applied to characterize a hybrid fiber-reinforced composite laminate subject to low velocity impact in this study. The hybrid fiber-reinforced composite laminate comprises unidirectional glass/epoxy and carbon/epoxy plies with a cross-ply stack pattern. Both impact-induced intra- and inter-laminar damages are successfully detected, and the damage evolution throughout the thickness is also evaluated. The interaction between the terahertz polarization and carbon-fiber orientation is investigated in detail. Inter-laminar damage at the interface and the intra-laminar damage close to the same interface can be differentiated via polarization-resolved imaging. With a parameter fitting method based on multiple regression analysis, delamination is characterized quantitatively. Terahertz C- and B-scan images clearly exhibit the propagation of the damage from the top to the bottom surface in three dimensions. (C) 2016 Elsevier Ltd. All rights reserved.