Numerical investigation on the failure phenomena of stiffened composite panels in post-buckling regime with discrete damages

• Progressive failure analysis of flat composite stiffened panels in post-buckling regime.
• Simplified discrete damage model.
• Sensitivity of the buckling onset to the damage locations.
• Sensitivity of the collapse load to different damage scenarios.

The aim of this work is to investigate the final failure response of damaged composite stiffened panels in post buckling regime under compressive load, by using progressive failure analysis (PFA) methodology. The selected panel is characterized by T shaped stringers and it is representative of the upper skin panel, toward the wing tip, of the wing box of a typical regional aircraft. PFA methodology has been applied in order to predict in addition to the initiation of the local failure also its propagation up to the final collapse of the panel, in presence of local damage (barely visible impact damage, BVID) and in post-buckling regime. For this purpose, discrete damages have been considered in the skin of the panel. According to the indications contained in many guidelines finalized to the preliminary design of composite structures, a simplified design model of BVID has been considered in this work, in particular a hole 1/4 in. in diameter has been used to simulate this damage. The collapse load of the panel has been evaluated considering different locations of a single damage and also considering multi-damage maps (the latter are more representative of a real damage scenario). The results of PFA presented in this work illustrate the combined effect of the reduction of the panel stiffness and of the damage propagation, and the sensitivity of the buckling onset and of the residual strength of the panel with respect to different damage locations and damage density.