Residual strength estimation of composite three-stringer panel subjected to low-velocity impact

Abstract

The presented research proposes a computational method for conservative residual strength estimation without direct modelling of impact, based on “reversed” topology optimization. To demonstrate basic steps of the method and evaluate its efficiency, the real example of compression after impact (CAI) test of aircraft three-stringer composite panel with quasi-isotropic lay-up is considered. Impact on the skin from the outer side of epy panel leads to damage in all three components of the structure: skin, stringers and noodle. Nondestructive inspection and optical microscopy is used to evaluate dimensions and damage distribution of formed defect after impact for selection of optimization volume in the model. Visually observed damaged zone on stringer and skin dent geometry also used for a conservative selection of optimization volume for the search of the “worst case” damage distribution. Topology optimization procedure shows that the most critical matrix damage distribution is the relatively uniform stiffness reduction of the ±45° layers in a composite layup. Fiber-dominant damage modes appear in 0°-oriented plies next to the noodle. Both matrix and fiber damages are enhanced in the area of stringer noodle due to stress concentration.