Two-dimensional quasi-static debonding in GFRP/balsa sandwich panels

The two-dimensional (2D) debonding behavior of GFRP/balsa sandwich panels presenting embedded circular disbonds at the face sheet/core interface was experimentally investigated. The bottom of the panels was fixed and out-of-plane quasi-static tensile loads were applied to open the crack. Two different face sheet configurations were studied. The first consisted of a pure woven ply layup while in the second, layers of continuous filament mat (CFM) were placed above and below the woven plies. The inclusion of CFM layers at the face sheet/core interface resulted in an enhanced fracture behavior exhibiting improved load-bearing performance and significant crack arrest. In-plane stretching strains appeared in the deformed face sheets due to the 2D embedded nature of the crack. The magnitude of the stretching was quantified based on the in-plane strains monitored throughout the experiments. As a result of the stretching, shear mode contributions were activated, causing the initiation of secondary cracks in the pure woven configuration and crack migration in the woven/CFM configuration. The migration in the latter occurred from the face sheet/core interface to the woven/CFM interface, generating dense fiber-bridging. This intensified fiber-bridging was found to be the main cause of the already-mentioned improvement in the fracture performance of the woven/CFM configuration.