Research On High-speed Impact Damage Of Composite Laminates

Composite materials have the advantages of low density,high specific strength,high specific modulus,good fatigue resistance and corrosion resistance.Composite materials have become one of the four major aviation materials in the new generation of aircraft.During the service of the aircraft,it is inevitable that it will be hit by foreign objects,and the composite material is prone to unobservable damage,such as fiber breakage,delamination and matrix cracking,and even severe structural damage.In this paper,glass fiber woven composite laminates are used as research objects,and the effects of the thickness and hybrid effects of laminates on the high-speed impact damage characteristics and transformation mechanism of protective structures are studied.First,five continuous-thick glass fiber woven composite laminates were prepared using the vacuum hot-press forming process,and then 2 mm thick hybrid laminates containing one layer of 304 stainless steel mesh and three layers of 304 stainless steel mesh were prepared.Secondly,the one-stage light gas gun system was used to conduct impact experiments.Hemispherical-nosed projectile were used to impact five thicknesses of glass fiber woven composite laminates.The impact process was recorded by a high-speed camera and the ballistic limit velocity was calculated using a fitting formula.The damage of the laminate and its mechanism characteristics were analyzed by a microscope.The study found that the ballistic limit of the laminate increased linearly with the thickness.The energy absorption rate of the thicker plate is slightly larger than that of the thin plate.The main damage modes of laminates are fiber bundle tensile fracture and shear fracture failure,matrix crack,fragmentation and delamination damage.There are two reasons for the delamination damage.One is the delamination damage caused by multiple reflections of tensile stress waves in the laminate;the other is the difference in the amount of deformation of each fiber layer leading to the shear damage of the interlayer matrix and the delamination damage.Thicker plates are more likely to cause large area delamination damage than thinnerplates.Finally,high-speed oblique impact tests were performed on 2 mm thick glass fiber composite laminates and glass fiber / metal mesh hybrid laminates containing one and three layers of 304 stainless steel mesh.The study found that the ballistic limit of the laminate with three layers of stainless steel mesh was the highest,and the second was the lowest,and that of the laminate with one layer of 304 stainless steel mesh was the lowest.With the increase of the speed,the damage area of the laminated plate without 304 stainless steel mesh increased first,then decreased,and then it tended to be constant.After adding 304 stainless steel mesh,the laminate will cause greater delamination damage and absorb more energy during impact.When the oblique impact is at a lower speed,the laminate has a weaker resistance to deformation and produces ductile failure.The main damage modes are matrix crack,matrix fracture,delamination,fiber tensile fracture and wire tensile fracture.When the speed is far above the ballistic limit,the laminate is affected by the strengthening of the strain rate.The laminate's resistance to deformation is enhanced and brittle failure occurs.The main damage modes are matrix cracks,matrix breakage,delamination,fiber shear fracture and wire shear fracture.