| Carbon fiber has the characteristics of light weight,high strength and high modulus.The composites prepared by carbon fiber have broad application prospects in the fields of aerospace,transportation and special protection.The triaxial woven fabric contains three groups of yarns in different directions.The new weaving method of the fabric makes its structure contain hexagonal holes,which can reduce the weight and have better mechanical properties.Triaxial woven fabric for carbon fiber combines the characteristics of carbon fiber and the characteristics of fabric structure.Compared with traditional fabric,carbon fiber triaxial woven fabric has the characteristics of ultrathin and quasi-isotropic in mechanics,which makes it popular in the aerospace field.However,the weaving process for triaxial woven fabric is complicated,such as the friction and fracture of carbon fiber during the present weaving process.Also,little attention has been paid to the geometric structure model of carbon fiber triaxial woven fabric.In addition,there are few studies on mechanical properties and corresponding finite element analysis model of carbon fiber triaxial woven fabric composites.Here,we solved the problem of difficult for carbon fiber weaving and studied the weaving process of triaxial woven fabric for carbon fiber using the principle.The geometric structure of the fabric was modeled to build the relationship between the shapes of the fabric with parameters of weaving process.Finally,the mechanical properties of the triaxial woven fabric composite for carbon fiber were studied,the material three-dimensional mesoscopic model was established and the finite element analysis was carried out.Moreover,the three dimensional mesoscopic model was established and finite element analysis was carried out.Firstly,according to the weaving principle of triaxial woven fabric,the necessary mechanism of machine for carbon fiber was designed,including the yarn storage device for carbon fiber which also can adjust the warp tension,the mobile heald frame which can match the movement characteristics of carbon fiber yarns,the weft density controlling and fabric finishing device and the winding mechanism for carbon fiber triaxial woven fabric.These mechanisms form a triaxial woven fabric loom for carbon fiber weaving.In addition,the warp tension required during weaving process was calculated.The compensating length required before and after weaving was solved by connecting the carbon fiber yarns with fixed pulleys and weights.The parameters of the control unit in the weft density controlling and fabric finishing device are calculated.The relationship between the diameter of the winding roller,the step angle and the pulse number of the stepping motor,the center distance between the yarns in the fabric were analyzed.Secondly,the plane and cross section unit cell models of carbon fiber triaxial woven fabric were established respectively.The models were verified by measuring the parameters in fabrics which come from the loom.In the model of plane geometry structure,the relationships among the width of carbon fiber yarn,weaving angle,the side length of hexagonal hole,the area of hexagonal hole,the area of unite cell,and the porosity of fabric were established.In the model of section geometry structure,the relationship between four basic parameters（the width of carbon yarn,the weaving angle,the angle corresponding to the section arc and the interweaving angle）and fabric parameters（The distance between the warp yarns of the same group,the density of fabric,the thickness of fabric,the degree of yarn buckling,the coefficient reflecting the degree of yarn flattening and the coefficient reflecting the size of the gap between interwoven yarns）were established.Then,the tensile properties of carbon fiber triaxial fabric composites were studied.After the triaxial woven fabrics with different specifications were prepared as composites by resin film infiltration molding process,tensile tests for composites were performed at different angles.When the width of the carbon fiber yarn increases,the maximum tensile load and the maximum displacement of the composites along the 0° direction increase,while the tensile strength decreases.Compared with the 0° direction,the specimen stretched along the 90° direction can obtain a larger displacement,but the tensile strength is weakened.According to the damage morphology of the material,the 0° direction tensile material can be summarized into three stages of failure.The first stage is mainly matrix fracture,the second stage is inter-yarn slipping,and the third stage is mainly fiber fracture until failure.Materials along the tensile direction of 90° can be divided into two stages of failure.In the first stage,the failure occurs as matrix stripping and the micro-deformation of hexagonal hole.in the second stage,the large deformation of hexagonal hole leads to disconnection of yarns which leads to the failure of composites.In addition,the flexural properties of hybrid fabric composites were studied by reinforcing unidirectional fabrics composites with triaxial woven fabric.When the fiber volume content is reduced by 18.44%,the bending strength can reach to 99.18% of original composite by optimizing the layering structure sequence.The bending mechanism of triaxial woven fabric with different layering sequence in hybrid structure was studied by using DIC technique and acoustic emission technique.When the triaxial woven fabric is close to the top layer,there will be a long time of violent fluctuation near the maximum flexural load,because there are many signals of matrix fracture and fiber-matrix debonding in the material,and intermittent fiber fracture occurs in the upper two layers of the sample.There are more signals of matrix fracture and fiber-matrix debonding in the composites and the intermittent fiber fracture occurs in the upper two layers of the sample.When the triaxial woven fabric is in the middle layer,the curve of Load-displacement curve is similar to that of the unidirectional fabric composite which decreases rapidly after the maximum load.Besides,the fluctuation near the peak value is not obvious.When the triaxial woven fabric is close to the bottom layer,the material can obtain more strain with the increase of deflection,and the energy absorption of the triaxial woven fabric increases significantly.When the material load reaches the highest point,different from the intermittent failure of the material when it is close to the top layer,the fibers under stress together will produce damage at the same time in the later stage.Finally,the three-dimensional model of carbon fiber triaxial woven fabric composite was established by combining the cross section geometric structure model and the interlacing form of triaxial woven fabric in the composite.Then,this three-dimensional model was divided into carbon fiber and matrix according to the fiber volume fraction by testing.The finite element analysis was carried out on the mesoscopic model with the help of software.The simulation results of resin and carbon fiber yarn in the material were summarized,and the damage mechanisms of the triaxial woven fabric composites prepared by carbon fiber with different specifications under different tensile angles were analyzed.When the material is stretched along the 0° direction,the carbon fiber yarns play a dominant role in the tensile process,the resin role is weak,and the two yarns in the vertical direction of the yarn play a major role,the other four yarns provide part of the stress.However,both yarn and resin play a significant role in the tensile process at 90° direction. |
PDF Full Text Request