Preparation And Mechanical Properties Of Pre-bend Pillar Yarn Structured Three-dimensional Woven Spacer Composites

Three-dimensional woven spacer composite is a new type of hollow sandwich composite made by using three-dimensional woven spacer fabric as reinforcement and resin matrix.It is not only light weight,high strength and heat insulation,but also has good integrity and strong designability.Because of its excellent performance,it is widely used in radar antenna,rail transit,ships and wind power blades and other fields.In the process of preparation of three-dimensional woven spacer composite materials,extrusion during transportation and other processes will make the yarn of the fabric C-shaped bending,and the bending structure will have a certain impact on the compression and impact properties of the composite materials.In order to understand the effect of the curved structure of the yarns on the mechanical properties of the composite materials in detail,epoxy resin was combined with three-dimensional woven spacer fabric by hand paste forming process in this paper,and the material was compressed and preshaped before curing,so that the yarns presented C-shaped bending in the latitudinal direction.By adjusting the compression degree of the pre-shaped stage of the 3D spacer composites,the 3D spacer composites(3DWSC-12,3DWSC-9,3DWSC-6)with different core height and yarn bending degree were obtained,which were compared with the uncompressed 3D spacer composites(3DWSC-15).Study the influence and change of core layer height and yarn bending degree on quasi-static and dynamic compression properties,low speed impact properties and bending properties of materials.First,flat compression properties,side compression properties and dynamic compression properties of four three-dimensional spacer composites under the 50%stress level of flat compression failure limit were tested,and their failure modes were studied.The results show that after compression,the flat compression properties of 3D spacer composites are firstly affected by yarn bending after compression,and the flat compression properties of 3D spacer composites decrease.The flat compression strength of 3DWSC-12 and 3DWSC-9(0.39 MPa,0.52 MPa),Compared with 3DWSC-15(0.72 MPa),it was decreased by 45.8%and 28%.The flat compression performance of 3DWSC-6(1.04 MPa)was 44.4%higher than that of3DWSC-15(0.72 MPa).The flat pressure failure mode of the material changes from yarn fracture to yield failure,and the material has a long deformation platform after yielding,showing better energy absorption characteristics.In addition,the fatigue property of the material is decreased,and 3DWSC-9 and 3DWSC-6 will fail when the material strain exceeds the limit after 500 cycles.Secondly,the mechanical response of four kinds of three-dimensional spacer composites under the impact of 5 J and 10 J energy at low speed was tested,and the residual strength of the materials after impact was tested to evaluate the damage degree of the materials.The results showed that when the precompression degree was less than 40%,the increase of the bending degree of the column yarn would improve the toughness of the material and reduce the damage of the material under the impact of lower energy(5 J).The residual strength of3DWSC-12 and 3DWSC-9 were 70.1%and 78.6%of the initial strength,respectively.3DWSC-15 was only 66.4%of the initial strength.When the impact energy increases to 10J,the contact force between the material and the punch increases with the increase of yarn bending degree.The maximum contact force of 3DWSC-9 is 1078 N,which is 21.1%higher than that of 3DWSC-15(890 N),showing stronger impact resistance,and the remaining strength is only 28%of the initial strength.When the compression exceeds 60%,the hollow ratio of 3DWSC-6 is greatly reduced and the rigidity of the material is improved,showing stronger impact resistance and energy absorption capacity.Finally,the warp and zonal bending properties of four three-dimensional spacer composites were tested.The results show that with the increase of compression degree,the peak load of the three-dimensional spacer composites decreases.The peak meridional and zonal bending loads of 3DWSC-15 were the largest(194.2 N and 154.4 N,respectively),while the peak meridional and zonal bending loads of 3DWSC-6 were the smallest(only 108 N and94.3 N),which decreased by 44%and 38.9%compared with 3DWSC-15.In addition,the warp and zonal flexural stiffnesses of 3DWSC-6 were 1.21 N?mm~2 and 1.14 N?mm~2,respectively,which were significantly higher than those of 3DWSC-15.