Tensile Properties Of Warp-knitted Automotive Interiors And Finite Element Study

With the rapid development of the automotive industry,people’s consumption level has increased significantly and there are new requirements for automotive interior materials.With the advantages of excellent performance,light weight,environmental protection and low cost,textile materials have gradually replaced metal and leather as interior materials in cars.Textile fabrics,especially knitted fabrics,have good elasticity,ductility and many variations of patterns,which can well meet the requirements of automotive interior fabrics for beauty,durability and comfort,and have a good prospect in the field of automotive interior trim.Automotive interior trim materials have certain requirements for mechanical properties,and processing is often done by moulding,injection moulding and other processes,and knitted fabrics are compounded with other materials,often requiring the elasticity,softness and strength of the fabric material to meet the moulding requirements.Traditional methods of exploration for the design and optimisation of the mechanical properties of material structures have mostly used experimental methods,resulting in repetitive and inefficient work.The finite element method can be used to simulate and predict the force process of the material and optimise the structure and parameters of the material based on the results,effectively reducing the number of experiments and time costs and improving the efficiency of the design.This thesis focuses on the investigation of the tensile properties of warp-knitted materials for automotive interiors.A three-comb warp-knitted tissue is designed as a material for automotive interiors,and in order to achieve the recycling of waste polyester,the knitting raw materials are compared with virgin polyester and recycled polyester.The tensile properties of the composite were tested by laminating the warp-knitted fabric with non-woven fabric and sponge respectively;then the single cell model of the three-combed warp-knitted fabric was modelled based on rhino 3D modelling software;finally the mechanical properties of the warp-knitted fabric were simulated based on ABAQUS finite element analysis and the deformation mechanism of the coils during the stretching process was analysed,and the following conclusions were obtained:(1)The spinning process and basic performance parameters of polyester,the raw material of the fabric,were explored,and the production process parameters were determined,in which the drying temperature of virgin polyester and recycled polyester was 180 °C,the crystallization temperature was 175 °C and the oven temperature was290 °C.The melting point,crystallinity and orientation of the virgin and recycled polyesters were characterised using DSC and X-ray diffractometry,and the DSC and XRD curves of both were found to be in general agreement.The melting point of the recycled polyester was 250.09 °C and that of the virgin polyester was 253.26 °C.The crystallinity and orientation of the recycled polyester were slightly lower than those of the virgin polyester,49.92% and 46.27% for the virgin polyester and 98.18% and 97.98%for the recycled polyester,respectively.Due to the secondary recycling process,the breaking strength and elongation of the recycled polyester are slightly worse than that of the recycled polyester,and the dynamic friction coefficient is slightly higher than that of the latter,at 0.24 and 0.23 respectively.(2)Based on the two polyester materials,a three-combed warp-knitted fabric was designed and woven,which was laminated with non-woven fabric and sponge respectively.The tensile properties of the warp-knitted fabric,non-woven composite fabric and sponge composite fabric were tested in 0°,30°,60° and 90° directions.It was found that the non-woven composite fabric had the best breaking properties at different angles,with the strength stable between 700 N and 1050 N.The elongation at break varied between 60 mm and 75 mm,and the breaking strength of all six specimens was greatest in the 90° direction.The Poisson’s ratio of the materials was tested and found to be stable at around 0.3.The mechanical parameters of the fabrics were fitted based on the Fourier model and Exponential function.(3)The surface geometric information of the interior warp knitted fabric was collected using a polarising microscope,and the width,height and depth of the coils were measured respectively to obtain the geometric structure parameters of the warp knitted fabric;then the coils and extension lines of the three combs in the three-comb warp knitted fabric were modelled separately,and the centre line of the single cell model was constructed using NURBS curves based on the obtained type value points and control point coordinates,and the spatial The curve equation of the coils was fitted;the yarn cross-section was formulated as a circle,and the model of each comb was completed by sweeping,and finally the three-dimensional spatial model of the whole three-comb fabric was constructed by means of an array.(4)Based on the single cell model of the three-combed warp knitted coil,the finite element analysis software ABAQUS was used to simulate the tensile properties of the material in the longitudinal and transverse directions.The morphological changes of the warp-knitted coils during the stretching process were compared and analysed,including the changes in width,height and tilt angle of the coils,and the central trajectory model of the coils was extracted.It was found that there was no obvious trend in the overlapping part of the coils during stretching due to the interference of the backcomb coils;the width of the separate part of the coils decreased and the height and tilt angle of the coils increased as the stretching progressed.At the end of longitudinal stretching,the width of the individual part of the coil shortens by 88.65%,the height of the coil increases by 26.96%and the angle of inclination of the coil changes by 15.91°.When the transverse stretching was completed,the width of the individual part of the coil was shortened by 58.37%,the height increased by 29.90% and the tilt angle of the coil changed by 43.48°.This study has certain reference significance for the production and application promotion of textile materials for automotive interiors,while the construction of a threecomb warp knitted fabric model helps to predict the mechanical properties of complex multi-comb knitted materials,laying the foundation for future structural design and performance optimisation of materials for automotive interiors.