Simulation Of Impact Damage And The CAI On Stiffened Composite Panels Structures

Stiffened composite panels are the typical composite structure type on aircraft. It's unavoidable for the aircraft to encounter low-velocity impact during its manufacture,assembling and service.It will cause fibre broken, matrix cracking and delaminatiion, leading to the reduction of strength and stiffness. A low-velocity impact with sufficient energy will cause damage in the composite structure, which may be barely visible. To develop structures which are more damage-tolerant, it is necessary to understand how the damage is caused and how it can affect residual performance. Many investigations of impact damage in carbon-fibre composites are based on testing of small laminates rather than full-scale structures. Several important issues regarding simulation of composite structure due to low-velocity impact were investigated including contact law, damage initiation and the corresponding change of stiffness, and damping. The analysis yields analytic functions describing the history of contact force, displacements of the impactor and the panel in three main directions.This paper is focusd on strengthen our understanding of the factors which control impact damage in composite structures, particularly the effects of geometry and substructure. The structural elements chosen for the investigation comprised a series of stiffened composite panels, representative of real aircraft structure. The effects of geometry were investigated by impacting panels of different stringer spacing and skin thickness, and the effects of substructure by impacting the panels at different positions relative to the stringers. Besides confirming the relation between pti depth and damagedarea, impact energy, the more important thing is to confirm the CAI of composite panels and stiffened composite panels, gaining the relation between CAI and damage size. After impact, the compressive strength of composite structure reduced substantially, so the CAI become the standard method to judge the severity of impact damage.