Investigation On Damage In Carbon Woven Composite Laminates Caused By High Velocity Impact

Carbon fiber reinforced composite(CFRC)has been widely applied in aircraft structures.The damage modes,failure mechanisms and damage extent of CFRC laminates under high velocity impact,such as warhead fragmentation and gun projectile,are determined by the characteristics of projectile and properties of laminates.In this thesis,the damage behaviors and failure characteristics of the woven carbon/epoxy composite laminates target structure under high velocity impact of warhead fragments or ballistic impact are investigated.Two opposite sides,the fragmentation leth ablity and the impact resistance of target plate are systematically discussed.This research provid an important reference for the design of warhead fragmentation,and also can provide valuable guidance for the aircraft structure design to improve the anti-shock impact performance.Based on gas gun impact tests,taken the experimental results of gun shooting and warhead static explosion as references,this thesis analyzes the damage morphology and failure modes,presents the investigation of damage mode prediction on basis of impact energy.The prediction results of failure modes are further introduced into numerical analysis.Combined with the experimental tests,the high velocity impact damage characteristics of the carbon woven composite laminates and hybrid laminates are investigated.This research work can provide valuable guidance for improving the impact performance of the warhead fragment on the laminates target structure and reducing the vulnerability of the aircraft carbon woven composite laminates.The main work is listed as follows:(1)Using the gas gun to drive 5 kinds of projectiles,60 impact tests are carried out on the weoven carbon fiber resin epoxy laminates with the thickness of 5 mm and 7 mm,respectively.The damage morphologies are analyzed,and the impact damage modes are classified as back-crack type,back-burst type and penetrated type.The damage modes and mechanisms involved in each damage morphology are investigated.The variation of impact damage morphology and impact damage of the laminates with the kinetic energy of the projectile are given.The correctness of the obtained impact damage law at the installation impact velocity is verified by the artillery firing and the warhead static test.The research indicates that the projectile specific kinetic energy is one of the decisive factors of the high velocity impact damage morphology and damage extent.The damage morphology,damage modes and damage extents are different when the kinetic energies are different.When the kinetic energy of projectile is lower,the laminate thickness is different for the damage morphology.The damage type for the thin plate is normally back-burst type,and the damage type for the thick plate is back-crack type or back-burst type.Under a high specific kinetic energy,the damage modes for both the thin and thick plates are penetrated type damage,and the impact damage area is relatively small.(2)Theoretical analysis on the energy consumption of impact damage is carried out.Based on the specific kinetic energy of projectile and the penetration kinetic energy of the target plate,an engineering method for the prediction of impact damage mode and extend is proposed.According to the damage modes and the mechanism analysis of different specimens,combined with the stress wave theory and energy conservation law,the analysis of damage energy consumption and failure modes is carried out.A simplified model of impact damage area is established,the main damage modes in each area are determined,and the influencing factors of geometrical dimensions are analyzed for each area.Based on the definition of specific kinetic energy,a method for predicting the impact damage mode and its range is proposed.The accuracy and credibility of numerical simulation is improved by introducing the proposed method.(3)The prediction results of impact damages are applied to numerical simulation model and the effect of projectile characteristics on impact performance is studied,which provide important guidance for the warhead design and the improvement of destructive effect to composite targets.By comparing the numerical and experimental damage morphology and damage extent,the feasibility and applicability of the modified numerical model are verified.The damage-mode based constitutive relation is obtained by VUMAT programming,and the numerical simulation model is solved by ABAQUS/Explicit.The effects of projectile velocity,contact area,material properties and close-range interference on impact damage are further numerically discussed,which provide kinds of useful guidance the design of fragmentation and killing warhead,and some guidance have been used in warhead design.(4)Impact performance of hybrid laminates under high velocity impact is further investigated.Important guidance and suggestions on the tough material selection and the pavement method are obtained for decreasing the extent of impact damages.Based on experimental tests and numerical simulation,the impact performance and failure mechanisms of two kinds of carbon fiber reinforced hybrid laminates are investigated.It is concluded that the delamination between mixed interfaces in hybrid laminates is common.The hybrid interface delamination in E-glass/carbon fiber reinforced hybrid laminates is even worse than that of Kevlar/carbon fiber reinforced laminates.When E-glass or Kevlar fibers are laid on the impact back surface,the delamination extent is particularly serious.With the increase of the impact velocity,the delamination extent between the mixed interfaces is reduced for various lay-up methods.Under the same impact velocity,the impact performance is improved for both the laminates with reinforced E-glass or Kevlar fiber on the impact front surface.The layer is effective for reducing the impact damage,but this effect is only obvious when the impact velocity is relatively low.In order to reduce the impact damage extent,it is more suitable to lay the Kevlar fiber,than the E-glass fiber,on the impact front surface.The innovation and new contributions of this research are listed as following:(i)Based on projectile specific kinetic energy and target penetration kinetic energy,an engineering damage prediction method is proposed,for the first time,to predict the damage extent by using a small number of condition parameters.(ii)An improved numerical simulation method based on various failure criterions for different damage modes is presented,which improves the singularity and blindness of the traditional damage criterions.(iii)Based on the comparisons of impact performances between various hybrid laminates,the design suggestions and references for hybrid structures,such as the selection of tough materials and the determination of lay-up methods,are provided.These methods and conclusions exhibit a certain of reference value for theoretical analysis and engineering applications.