Damage Tolerance of Stiffened Skin Composite Panels

This work discusses design, fabrication and damage tolerance evaluation of co-cured skin stringer carbon fiber composite panels. Such stiffened panels are typically found in aircraft wing skins. Composite panels representing a portion of an aircraft wing box are designed and fabricated using Carbon fiber and epoxy matrix using resin infusion process. Fixtures to support the panels during low velocity impact tests are also designed and fabricated. A drop tower is used to conduct impact tests. Panels are subjected to various impacts to study the effect of impact energy on damage visibility and damage size. Impacts are also categorized according to their location: (a) Impact exactly above stringer, (b) Impact above skin, and (c) Impact above stringer flange. The extent of damages is studied based on non-destructive inspection techniques such as ultrasonic inspection. Further, one of the panels containing impact damages is subjected to residual strength test. Displacements and strains are measured using digital image correlation technique and resistance strain gages. Finite element model of the panel is also developed. Deformations and strains obtained from FE simulations are compared with test data. Results show that impact damages did not alter the load path significantly in the composite panel