Research On Low Energy Impact Damage And Dynamic Response Of Aeronautic Typical Composite Construction

Composite material has the advantage of high strength,high stiffness,high designability and good fatigue resistance which lead to the wide applications in aerospace technology,marine engineering,weapons equipment technology,civil construction,transportation and daily life.However,during the manufacture,use and maintenance,composite materials is easily subject to many kinds of low-energy impact damage caused by foreign objects.Such depth of dimples formed by the impact of generally less than 0.5mm and they are hardly to find visually,but inside the composite material maybe has undergone fiber compression,fiber fracture,matrix compression,matrix cracking and delamination damage,which lead to mechanical properties significantly decreased,resulting in load carrying capacity decrease and seriously affect flight safety.The low energy impact test,the residual compressive strength test and numerical study of the composite sandwich plate and the composite foam sandwich structure are carried out in this paper.The main research contents of this paper include:(1)Experimental study on low energy impact of composite laminates.Low energy impact test of four typical structure of 64 composite specimens were carried out in different impact of energy,different punches,different structural laminates.The impact force versus time curves,displacement versus time curves,strain versus time curves,impact force versus displacement curves were got.The effects of different variables on the low energy impact damage and dynamic response of composite laminates are studied.(2)Experimental study on low energy impact damage resistance and damage tolerance of composite laminates.The pit depth and delamination area are regarded as damage resistance.The contact method was used to measure the depth of the pit to research the relations of impact energy and pit depth,punches' shape and pit depth.The Ultrasonic C-scan was used to detect the delamination area of nondestructive testing.MATLAB code programming and Image-pro plus6.0 pixel processing method were used to obtain more precise delamination areas.The residual compressive strength was used to characterize the damage tolerance.It studied the effect of different factors to damage tolerance.(3)Numerical simulation of low energy impact damage of composite laminates was carried.The results showed that the long axis of delamination associated with the direction of lower layer.Delamination does not occur between the two-ply with same direction.The larger angle between the upper and lower layer's long axis,the greater the delamination area.To apply ± 45 ° in the structure's outermost plies can significantly improve the impact resistance.To apply 45°/0° or-45°/0° in the structure's outermost plies can significantly improve the residual compressive strength.(4)Experimental study on low energy impact of composite foam sandwich panels.To study the effect of the impact energy,foam type,punch type,eleven low energy impact tests of foam sandwich panels were carried.The impact force versus time curves,displacement versus time curves,impact force versus displacement curves,strain versus time curves,lower panel displacement versus time curve,the amount of foam core compression were obtained.(5)Numerical simulation of low energy impact of composite foam sandwich panels.To establish composite foam sandwich panels low energy impact damage finite element model,using Hashin failure criteria and adhesive contact model.According to the experimental result of the test 101-16mm-7 and the test 201-16mm-17 J,to verify the accuracy of the model,and got the final failure mode of the upper and lower panels.(6)Typical aerospace composite structures low energy impact and residual strength numerical Analysis.Tool fall was simulated in the condition of the 12.7mm punch and 8.1J impact energy,the low energy impact and the compression after impact of a type of unmanned aerial vehicle foam sandwich structure on rudder and aileron composite material were simulated,obtained the impact damage for each sub-layer,the core material destruction and the residual compressive strength of the structure.