Failure Analysis Of Composite Repair Structures Under Different Impact Velocities

Since 1940 s composite has been used in the fields of aviation and electronic,with the deepening of the understanding of composite materials with superior performance, now composite material has been widely used in aerospace,shipbuilding, protective equipment, machinery manufacturing, and other fields.With the application of composite materials in aircraft structure and protective equipment, more and more attention has been paid to the impact damage of composite materials. Composite laminates are made of two or more than two layers.The different forms failure of fiber breakage, matrix cracking and delamination are easy to occur between the fibers, the fiber and the matrix, and the layers. In order to improve the impact resistance of composite materials, the matrix of high modulus and high strength is usually used, and the fiber content are increased in a certain range.Impact damage can be divided into three types: high energy, medium energy and low energy impact damage. High velocity impact damage, such as bullets,impact of high-speed particles can cause laminate penetrating injury, and the emergence of small range of hierarchical and flat fiber fracture; medium impact energy does not occur through injury, near impact zone appears broken fiber,laminate bending deformation caused by a wide range of stratification and the fibers in the back of laminates fracture. Low energy impact damage is not visible damage,in the composite material appears the matrix cracking or minor fiber breakage.In this paper, the failure of each sub layer under the impact of composite material repair structure is studied.First, this paper establishes the low velocity impact of composite laminate model, get the bullet force-displacement curve and the validity model is verified by comparing the numerical results and experimental results.Secondly, this paper establishes a bullet impact composite repair structure model, and the bullet medium velocity impact composite repair structure model,analysis of the element failure in each motherboard sub layer in the process ofimpact and influences of damage holes on the failure result.Finally, the effects of different shapes and sizes of patch on the repairing structure are analyzed in this paper.