Damage Tolerance and Residual Strength of Composite Airframe Materials and Structures

Abstract

The extend of impact damage in solid composite or sandwich structures depends on the materials, the stacking structures impact damage/growth in bay or stringer region is well detected by ultrasonic sequences, the size, mass and velocity of the impactor and the component ability to 0absorb the shock. The resulting complex interaction makes the forecast of damage and its growth under fatigue loading difficult. Impact damage is most critical for sandwich, when the skin remains intact. Except of a small dent or blister in the surface the impacted zone is often no visible or barely visible, but damage may grow under fatigue loading to a critical size and endangers the component. In stringer reinforced inspection. In sandwich/ structures with foam core delaminations are detected around the impact zone between skin/core and local buckling of delaminated skin layers triggers its progress. With Honeycomb core impact delaminations are hardly detected. The core is crumpled in the vicinity of the impacted zone and the elastic support is reduced. Under compressive loading the core shrinks in thickness direction and the skin buckles in core direction. To reduce the testing amount the analysis tool CODAC was developed and will be used in the frame of a Concurrent Integrated Engineering Process to quickly evaluate the impact behavior of stringer-stiffened panels due to low-velocity impact and will be extended to sandwich structures.