Preparation And Compressive Properties Of Honeycomb Three Dimensional Braided Composites

Honeycomb structure composite materials are widely used in aerospace,rail transit and construction engineering due to its advantages of heat insulation,shock absorption and noise reduction,lightweight and high strength.Traditional honeycomb composites,such as aluminum honeycomb and Nomex,are made of metal or paper.In this paper,the three-dimensional honeycomb braided preform with integrated braiding forming was studied,and the honeycomb composites were prepared,which provided conditions for further expanding the application field of textiles.This paper uses 1×1 Four step three-dimensional braiding technology and "yarn rotation principle" are used to braid honeycomb three-dimensional braided preforms with different opening angles and shapes.Three dimensional braided honeycomb composites with different opening angles and shapes were fabricated by VARTM process.The compression experiment of honeycomb 3D braided composites was carried out by universal testing machine.The strain of the composites during compression was recorded by 3D-DIC technology.The load displacement curve,stress-strain curve,maximum compression load and energy absorption were obtained.The failure modes of honeycomb 3D braided composites with different opening angles and shapes were analyzed,The causes of failure modes are analyzed.The experimental results show that the compressive load of honeycomb 3D braided composites increases with the increase of opening angle;At the same compression speed,the honeycomb three-dimensional braided composites with different cross-section shapes(circle,quadrilateral and regular hexagon)have the worst compression load capacity when the cross-section shape is quadrilateral,and the circular cross-section is the best.The compression failure modes of honeycomb 3D braided composites with different opening angles and shapes are almost the same,and the failure process can be divided into three stages.At the initial stage of loading,the honeycomb three-dimensional braided composites deform,and cracks appear in the surface of the resin matrix,and these cracks gradually extend to the interior of the fiber,leading to matrix cracking.After the end of the linear elastic stage,the composite enters the yield plateau stage,and the load peak value decreases with different amplitude,forming a disordered and non repetitive compression peak.After the yielding platform is finished,the material will lose its stability due to the plastic collapse of the main load-bearing honeycomb structure.Through 3D-DIC strain image analysis,the fracture failure of the composite is related to the shear strain distribution,the transverse and longitudinal local strain distribution is more uniform,the shear local strain appears the phenomenon of strain concentration,and cracks are easy to appear in the region of strain concentration,which leads to the shear fracture of the composite.From the strain image analysis,the three-dimensional honeycomb braided composites with different opening angles can be divided into three stages from compression cracking to failure.In the first stage,due to the bending deformation of the inclined wall of honeycomb structure around the end of the material,with the increase of deformation,the stress distribution on the surface is uneven,and the stress concentration occurs at the joint,which leads to the free end cracking of the composite;In the second stage,with the increase of load,the bending degree of the inclined wall increases and shrinks inward,but the elastic property of the material is limited.When the shrinkage limit is reached,the inclined wall will fail;In the third stage,after the failure of the main load-bearing structure of the composite,with the increase of the load,the overall bending of the composite increases,and the inclined wall of the hexagonal honeycomb shrinks inward,resulting in tensile force at the connection point.The tensile force is transferred to the non inclined wall of the honeycomb through the connection point,which causes the non inclined wall to bend inward and produce cracks.Because there is no non inclined wall in the circular and quadrilateral specimens,the ultimate failure of the composites is due to the plastic collapse of the inclined wall.After compression,the honeycomb 3D braided composites with different shapes and different opening angles collapse to one side,forming a lateralization band.