Numerical Study On Low-velocity Impact Behavior Of Carbon Fiber Reinforced Thermoplastic Composites

Carbon fiber-reinforced thermoplastic composite(CFRTP)has the advantages of recyclability,high impact resistance,good vibration damping characteristics,high fracture toughness and post-formability,and has shown huge performance in the process of continuous improvement in material performance and continuous reduction in material weight.The composite material structure has the risk of being damaged by the impact of objects during production,use and subsequent maintenance.It is of great engineering significance and theoretical value to conduct a complete and systematic study on the mechanical response and damage mechanism,energy absorption and conversion,and residual performance after impact of carbon fiber reinforced thermoplastic composites during low-velocity impact.According to this,this paper had done the following three aspects of research work:(1)Combined with several existing fiber-reinforced composite material damage models,a damage model more suitable for CFRTP laminates was established.By means of FEM,the effects of impact energy,punch weight and initial velocity on damage behavior of CFRTP under low-velocity impact were studied.As the impact energy increased,the damage degree,damage range,and impact duration of the laminate increased accordingly.At lower impact energy,the laminate mainly absorbed and transformed the impact energy by elastic deformation,while at higher energy it mainly absorbed the impact energy by damage and plastic deformation.The remaining compressive strength of the laminate decreased with the increase of impact energy,and the decline rate gradually slowed down.Under the premise that the impact energy was unchanged,changing the weight and initial velocity of the punch only affected the duration of the impact process,and had little effect on the impact damage characteristics of the composite laminate structure.As the mass of the punch increased,the duration of the impact increased.(2)By means of FEM,the influence of the number and position of[45]laminate on damage behavior of carbon fiber reinforced composites under low-velocity impact were studied.[45]laminate could increase the stress transfer area of laminates,effectively reduce the degree of damage and plastic deformation,and improve the impact resistance of laminates.With the increase of the number of[45]laminate,the impact resistance of the laminates increased.Under the condition that the number of[45]laminate was kept unchanged and the position was only changed,the[45]laminate was laid on the outermost layer of the laminates to effectively improve the impact resistance of the laminate.(3)By means of FEM,the effects of panel performance,impact energy and impact times on the mechanical response,energy response,impact damage and post-impact compression strength of CFRTP honeycomb sandwich panel were studied.The results showed that the performance of composite panel directly affected the impact resistance of the honeycomb sandwich panel.The retention rate of compressive strength of the honeycomb sandwich panel with the[45]4 thermoplastic laminates as the panel was as high as 53.6%.CFRTP honeycomb sandwich panels could absorb more than 80%of the kinetic energy of the punch,of which plastic deformation energy absorption accounted for more than 60%.When the impact energy exceeded the elastic deformation limit of the composite honeycomb sandwich panel,the same as the energy response of the laminate was that part of the impact energy was dissipated in plastic deformation,damage generation and evolution,friction and volume damping;the difference was that the honeycomb core layer would hinder the rebound of the composite panel,and part of the elastic energy was retained.Under the same impact energy,the more impact times,the higher the damage degree of the honeycomb sandwich panel.Under the same total impact energy,multiple low-energy impacts had less damage than a single high-energy impact.Under the impact energy of 1 J,the depth of the pit in the first loading was 0.94 mm,which was 0.46 mm and 0.78 mm smaller than those in the second loadings and third loadings respectively;the retention rate of remaining compressive strength in the first loading was 68.1%,which was 9.3%and 11.9%higher than those in the second loadings and third loadings respectively.