Prediction Of The Damage Of Composite Structure Under Low Velocity Impact

Composite can significantly increase the strength and reduce the weight of the structures, it’s widely used in the field of aerospace and manufacturing of key auto parts. But the resistance of composite structures to impact even low velocity impact is very low because of the severe anisotropy, and impact damage is prone to occur. So it’s necessary to research the damage form, evolution process and influence factors of composite structures under impact.Delamination is the main damage form of composite structures under low velocity impact, the paper firstly discusses the use of interface layer method in the study of delamination, establishes a model of composite DCB including interface elements, verifies the response of the model under tension and researches the influence of layer angle to the response. The influence of layer angle to the extension of delamination and the peak tension of the DCB model is obviously, peak tension decreases while the angle increases and changes rapidly when the angle is small and changes slowly when the angle is large.Establishes the overall three dimensional finite element model of composite laminates under low velocity impact using the finite element software Abaqus and material subroutine VUMAT, simulates the response and damage of laminates under low velocity impact, verifies the accuracy of the model and subroutine by comparison with the experiment results. The results shows that matrix cracking and delamination are the main damage of composite laminates under low velocity impact, matrix cracking appears earlier than delamination, delamination is caused by the matrix cracking and they interact with each other. The distribution of matrix cracking elements near the impact location is determined by both normal stress and shear stress, the distribution of matrix cracking elements away from the impact location is determined by normal stress, delamination appears between the layers whose layer angle change, and delamination is more serious in the side away from the impact location, the shape of delamination region looks like peanut and its long axis is along the fiber direction of the bottom layer.Finally studies the influence of velocity,projectile mass, material property and layer angle to composite laminates under low velocity impact, compares and analyzes the reason for the change of deformation, matrix cracking, and delamination of composite laminates, the velocity has great influence to the deformation and damage of laminates while the projectile mass has nothing to do with them;enhance the material property can effectively reduce the deformation and damage of laminates under impact, shear strength of laminates affects the distribution of matrix cracking elements near the impact location; layer angle has little influence to the deformation and matrix cracking of laminates under low velocity impact, while has great influence to delamination, delamination area increases while the layer angle increases, the area increases rapidly when the angle is small and changes slowly when the angle is large.