Research On Hypervelocity Impact Behaviour Of Flexible Braided Composite Structures

The safety of spacecraft and space stations is seriously threatened due to the numerous space debris produced by human spaceflight activities in the orbital space environment.Designing the shield for passive protection is an important and effective measure of protection.The flexible braided material has greater advantages in foldable expansion,envelope volume,expansion space and weight than metal material,which makes it become the preferred material in the future.Compared with the metal shield,the hypervelocity impact protection mechanism of the new flexible braided composite structure is still unclear,which restricts its further application.Therefore,it is of great theoretical significance and engineering application value to carry out the research on hypervelocity impact behaviour of flexible braided composite structures.In the thesis,the hypervelocity impact behaviour of flexible braided composite structures was studied based on smoothed particle hydrodynamics(SPH)-finite element method(FEM).The research focuses on the modelling method,the damage law and protection characteristics of the flexible braided material under hypervelocity impact,and the influences of projectile shape and attack angle on impact behaviour.The specific research contents and conclusions are as follows:1.A numerical simulation method for hypervelocity impact of the flexible braided material based on SPH-FEM was studied.Based on the hypervelocity impact damage characteristics of the flexible braided material,SPH and FEM were used to simulate the projectile and the flexible braided material.The modelling method of the flexible braided material considering the meso-structure was constructed.The results show that the simulation results are in agreement with the experimental results in the literature in terms of debris cloud characteristics,perforation characteristics and kinetic energy absorption,which verifies the validity and accuracy of the numerical simulation method in the thesis.2.The impact behaviours of the single-screen shield and double-screen shield under different structural parameters and impact conditions were studied.The results show that the perforation size and the kinetic energy absorption efficiency increases first and then decreases when the area density of the shield continues to increase.With the increase of impact velocity,the perforation size increases linearly.With the increase of impact angle,the projectile fragments slide and splash back,and the damage form and position of each layer change.The perforation shape changes from circular to oval and then to long strip.The number of fiber cloth layers penetrated decreases,and the kinetic energy absorption rate increases first and then decreases.The perforation size of the second screen of the low area density double-screen shield and the spacing are approximately linear.With the increase of the spacing between the two screens,the absorption rate of projectile kinetic energy increases.The perforation size of the second screen of the high area density double-screen shield first increases and then decreases with the increase of the spacing.The kinetic energy absorption rate of the projectile ascends with the increase of the spacing and tends to 100%.Filling aerogel between the screens can aggravate the fragmentation of the projectile and absorb small projectile fragments,thus enhancing the protective ability.3.The influences of projectile shape and attack angle on the impact behaviour were studied with a cylinder as a typical shape.The perforation area of the shield decreases with the increase of the length-diameter ratio.However,the fragmentation degree of the projectile decreases and the kinetic energy reduction decreases with the increase of the length-diameter ratio.The energy of the projectile is more concentrated and the penetration ability is stronger,which is not conducive to the protection of the subsequent screen.The hypervelocity impact behaviours of cylindrical projectiles with different length-diameter ratio are affected differently by attack angle.On the one hand,the long rod projectile with larger length-diameter ratio causes higher degree of fragmentation,greater damage of the shield and more dispersed energy,which is conducive to the protection of the subsequent screen.On the other hand,the disc projectile with smaller length-diameter ratio shows the opposite trend.