Study Of Fabric Ply Splicing Design And Mechanical Performance Of Complex Structure Stitched Composites

Carbon fiber stitched composite materials are manufactured by utilizing carbon fiber laminated technology and stitching technology.The exceptional abilities in laminated forming capabilities for complex components and great interlayer mechanical properties,making them have wide-ranging application prospects in hightech applications such as aviation and aerospace,transportation,and new energy.Recent research on carbon fiber stitched composite materials has mainly concentrated on the interlayer reinforcement mechanism of the introduction of stitched fibers,with comparatively less attention directed at the fundamental aspects of the profiling laminated carbon fiber fabrics in the manufacturing process of complex special-shaped stitched composites.Carbon fiber fabric profiling laminate is a critical process in the production of carbon fiber stitched composites.For complex shaped components,the limited deformability of carbon fiber fabric necessitates the use of cutting and splicing techniques to conform to curved surfaces while preventing wrinkling.Additionally,fabric setting method is needed during the lay-up process to ensure the fabric fits the mold surface and maintain the shape.Therefore,fabric ply splicing and shape preserving are the key technologies to realize the integrated manufacturing of composite with complex special-shaped structures.In response to the development requirements of carbon fiber stitched composite for landing gear of one type helicopter,this thesis mainly focuses on the design of carbon fiber fabric ply splicing and shape preserving method in the preparation process of complex-shaped stitched composite materials.By analyzing the ply splicing structure and laying process,and eliminating the influence of the stitched fibers,this research systematically scrutinized the effects of ply splicing structure parameters on the mechanical properties of composite materials and obtained the relationship between the ply splicing structure and the performance of composite materials.Based on the theory of three-dimensional(3D)fabric technology,a novel method for setting carbon fiber fabrics was proposed and the performance of shape preserving was evaluated.A virtual fiber embedding model for laminated fabric composite materials and a constructioneffect analysis method for laminated spliced fabric composites were developed,and the impact of splicing spacing on the tensile properties of composite materials was analyzed.The main research contents are as follows:(1)Laminated fabric setting design.We employed 3D weaving theory to design a two-layer layer-to-layer satin fabric structure and then manufactured a 3D carbon fiber hybrid fabric with a hot-melt fiber layer on the surface,and studied the properties of the shaping preserving after setting.Additionally,the influence of the hot-melt fiber content on the mechanical properties of the composites was analyzed.The research results indicate that the shape preserving performance of the new hybrid fabric is increased by 3 times in the warp direction and 2 times in the weft direction.When the hot-melt fiber content was greater than 4%,the interlayer peeling strength of the fabric was higher,and the bonding effect is good.(2)Study on tensile properties of laminated spliced fabric composites.Five different ply splicing structures were defined through analyzing the laminated structure.Systematic evaluation of the influence of splicing layer number,splicing depth,splicing angle,and splicing spacing on the tensile properties of laminated spliced fabric composites was done using experimental methods,combined with DIC strain technology and acoustic emission technology.Additionally,an analysis of the tensile response and failure mechanisms of laminated spliced fabric composites was conducted.The findings suggest that: the ply splicing significantly affects the tensile strength,however,its effect on the tensile modulus is minor.By increasing the number of consecutive splicing layers,the tensile performance of the composite materials was found to decrease,and the retention rate of the tensile strength is close to the proportion of the continuous layers of fabric at the spliced part.Improving the tensile strength of the composite material is possible by increasing the splicing depth.When the splicing spacing is greater than 30 mm,the tensile strength retention rate of the composite material tends to be stable,which is close to the proportion of continuous layers at the splicing point.At the same splicing spacing,the tensile strength of interlayer spliced and misalignment spliced fabric composites increases gradually when the splicing angle was reduced.(3)Study on compressive properties of laminated spliced fabric composites.This thesis focuses specifically on the number of splicing layers,splicing depth,and splicing angle on the compression properties of laminated spliced fabric composites.An analysis of the mechanical response and damage process of composite materials containing ply splicing under compressive loads was conducted.The research results show that: the ply splicing has a greater impact on the compression strength of composite materials,while its impact on the compression modulus is minor.Same-position multilayer splicing leads to a reduction of the compression strength of composite materials,and the retention rate of compression strength ranges between 80% and 85%.The compression strength retention rate of same-position interlayer splicing fabric composites is more than 70%.The compression strength retention rate of cross-position interlayer spliced fabric composites is more than 75%.With the same splicing angle and depth,the compression performance of cross-position interlayer spliced fabric composites is superior to that of same-position interlayer spliced fabric composites.(4)Study on in-plane shear properties of laminated spliced fabric composites.This thesis focuses specifically on the number of splicing layers,splicing depth,and splicing angle on the in-plane shear properties of laminated spliced fabric composites and the mechanical response and damage process of composites with ply splicing under shear load were analyzed.The research results show that: the ply splicing has a greater impact on the in-plane shear strength of composite materials,while its impact on the in-plane shear modulus is minor.The same-position multilayer splicing leads to a decrease in the shear strength of the composites,and the shear strength retention rate is greater than the proportion of the continuous layers at the splicing position.It was also found that when same-position interlayer splicing is performed,the retention rate of in-plane shear strength of the laminated spliced fabric composites is over 80%.Similarly,crossposition interlayer splicing also resulted in retention rate exceeding 80%.When the splicing depth was held constant,the shear strength of the ±45° cross-position interlayer spliced fabric composites was slightly lower compared to that of the 45° same-direction interlayer spliced fabric composites.(5)Structure-effect analysis of laminated spliced fabric composites.A quadratic spline function model was proposed to represent the yarn path,and the geometric model of the satin fabric structure was established.Based on this,a virtual fiber embedding model for laminated fabric composites was constructed,and a structure-effect analysis method of the laminated spliced fabric composite was performed.The influence of splicing spacing on the tensile properties of the composites was analyzed.The numerical simulation results show that: as the splicing space increases,the tensile strength of the composite materials initially decreases,then increases,and finally tends to be stable.The tensile strength of the composite materials decreases the most when the splicing spacing is 10 mm,with a decrease of 38.6%.Additionally,when the splicing spacing is greater than 30 mm,the decline value of the tensile strength of the composites decreases and tends to be stable,with the strength retention rate being close to the proportion of the continuous layer at the splicing part(80%).These numerical results entirely consistent with the experimental results.This thesis systematically examines the relationship between the ply splicing structure and the properties of composite materials using experimental and numerical simulation methods.A new method for fabric shaping is proposed,and a structure-effect analysis method for laminated spliced fabric composites is established to provide technical support for the development of complex special-shaped structure stitched composites.