Research Low-velocity Impact Damage Behavior On Composite Stiffened Panels

Because of the existence of stiffeners,the composite stiffened panel has improved antibuckling ability and maximum load capacity.It has been widely used in the main structure of the aircraft.The composite structure is sensitive to the external impact.When it is subjected to low velocity impact loads,delamination and matrix cracks will appear,which will reduce the residual compressive strength significantly.When the impact energy is small,the damage caused by the impact is not easy to detect,and it will influence the flight safety.There are many researches on the low-speed impact of composite laminates,but composite stiffened panels were rarely studied about this aspect.Composite stiffened panels are larger in size and more complex than composite laminates,they were used in the more critical position in aircraft.Therefore,it is of great significance to study the impact on composite stiffened panels for the structural design and routine maintenance of the structure.The aircraft will be hit during routine use.Common shock sources have rigid impacts and flexible impacts,such as the impact of gravel on the runway,the fall of the maintenance tool,the impact of birds and hail.In this paper,the impact damage characteristics of the composite stiffened panels are discussed from the low velocity impact of the rigid body and the high speed impact of the flexible body,taking into account the effect of the impact position,the impact velocity,the type of the stiffeners and other factors on impact damage.Considering that the damage of composite material under low impact is concentrated near the impact point,the finite element model of the composite stiffened panel is established by local refinement strategy.According to the characteristics of the bonding domain and the bonding contact model,the interface between the sub-layer of the skin and stiffeners adopt the bond contact model,and the interface between the skin and the stiffeners use the bond domain.The effectiveness of the numerical model is verified by comparing the calculated results with the experimental data.On this basis,the impact damage characteristics of the composite stiffened panels are studied.The results show that matrix tensile damage and delamination are the main manifestations.The tensile damage of the matrix is perpendicular to the fiber angle.The bending of the stiffener is prone to produce matrix tensile damage and delamination damage.Hail,as a flexible body,is constantly broken during the impact.Debris will take away part of the energy,which is the reason that the structure can withstand the impact of higher energy shock.Finally,the residual compressive strength of the stiffened panel with impact damage is studied.In the longitudinal compression loading of the composite structure,the tensile cracking of the matrix is the most serious.The compressive fracture of the fiber and the matrix are transverse through the structure to form a damage zone,the tensile cracking of the fiber is discontinuously distributed on the damage zone.When the composite stiffened panel is subjected to a lower impact energy,the damage under compression loading does not extend from the location of impact damage.When the impact does not cause damage to the stiffeners,the compressive bearing capacity of the structure does not drop obvious.