The Effect Of Yarn Reduction On The Deformability Of 2.5D Fabric And The Mechanical Properties Of The Composite

2.5 dimensional(2.5D)Angle interlock composite material has excellent mechanical properties,it will be expected to be widely used in aviation,aerospace,shipbuilding,construction and other fields.The improvement of the traditional weaving process and the related molding method,it can be manufactured with near net-shape to produce complex shapes and different sizes of the special shaped components and it has good design ability and strong profiling capability.The variable cross section 2.5D Angle interlock composite material manufactured by reducing warp yam method has good structural integrity and overall performance stability.In this paper,the demand of yarn reduction and the theroy of yarn reduction of 2.5D angle interlock fabric were analyzed,and the concept of geometrical structure of yam-reduction unit is introduced.The change of fabric meso-structure caused by different yam-reduction methods was analyzed.It was found that the unit yarn-reduction combined with The movement of the yam in the same layer could ensure the structure integrity and uniformity of the yarn interlacing structure.Then,the preform and its composite materials which accords with the gradient changes were manufactured by this method.According to the adopted method of yarn reduction,a 2.5D angle interlock meso-structure geometric mode was established based on the oval cross-section of the fiber bundle,and then the warp yams offset in the weft direction due to yam reduction were studied.Based on this,the meso-structure and unit model of the 2.5D angle interlocking composite yarn with varying cross section of the yam interlacing structure were determined.Finally,the elastic constants of the yam-reduction and non-yam-reduction units were predicted by the stiffness average method respectively.To evaluate the in-plane shear performance of 2.5D angle interlock fabric by the method of image frame,in order to reduce the error brought by the frame assembly,the existing frame assembly was modified to evaluate the effects of the yam reduction structure on the in-plane shear performance.The results show that the shearing angle(locking angle)of 2.5D interlock fabric is about 50 When it is in the locked state,and the shearing angle of the yam-reduction 2.5D fabric was reduced by 10%,showing weaker shear-resistant behavior.Before the locked state,the shear modulus is very small and it floats in the range of 0.05?0.1 MPa.When the shearing strain is greater than 0.5,but increased dramatically when the shear strain was larger than 0.5.At higher shear deformation,gaps between yarns are reduced,and yarn compaction occurs,so the fabrics exhibit stiffer material properties.In this paper,the warp tensile and flexural properties of 2.5D angle-interlocked composites before and after yam-reduction were tested.The failure of the yam-reduction composite mainly occurred in the variable cross-section area.Failure mode is a combination of fiber breakage,matrix cracking and fiber extraction damage.Then,a quantitative comparative analysis of the yam-reduction and non yarn-reduction angle interlock composite materials were carried out from the strength,modulus and tensile strain at break.The results show that the tensile strength and the longitudinal strain of the yam-reduced structure decrease by 9.0%and 8.0%,respectively.The initial modulus,flexural strength and flexural modulus increase by 6.0%,5.0%and 0.2%respectively.Therefore,this project proposes yarn-reduction unit method which has minimized the influence on basic mechanical properties of 2.5D angle interlocking composite.