Research On The Mechanical And Flame Retardant Properties Of Hemp Fiber Reinforced Composites For Rail Transportatio

Bast fiber reinforced composite materials have broad development prospects in the field of rail transit.The application of bast fiber reinforced composite is able to avoid the drawbacks of high production energy consumption,difficult to recycle,and harm to human health caused by production and utilization of glass,carbon and aramid fiber composite materials.However,the current bast fiber reinforced composite materials cannot meet the requirements of rail transit composite materials in terms of mechanical properties and flame retardant properties.Therefore,the development of high performance bast fiber reinforced composite materials is of great significance to the realization of green and sustainable development of the rail transit industry.In this paper,ramie fabric was used as the reinforcement and unsaturated polyester resin as the matrix to prepare ramie reinforced composite materials via molding process.The mechanical flame retardant properties of the composite materials were optimized and explored.The main research contents are as follows:(1)The basic properties of ramie plain weave cloth and unsaturated resin were tested,and the influence of molding pressure,fabric weight and number of layers on the tensile properties and bending properties of ramie fabric reinforced composites was explored by single factor analysis.The results show that the composite with best mechanical properties could be achieved by molding pressure of 20MPa,fabric surface density of 190g/m~2,and fabric plies numbers of 14.The tensile strength,tensile modulus,flexural strength,and flexural modulus of the composite are100.06MPa,8.31GPa,171.03MPa and 10.15GPa,respectively.(2)Phytic acid was used for the flame retardant modification of ramie fabric reinforced composites.The effect of phytic acid concentration on the mechanics and flame retardant properties of the composites was explored.The results show that the phytic acid significantly improves the thermal stability of the ramie fabric.The carbon residue on the surface of the fabric increases.Nevertheless,the contact angle and tensile strength decreased after the treatment.When the amount of phytic acid added is 3wt%,the carbon residue on the surface of the composite material changes from a relatively loose and porous structure to a dense and expanded structure after burning.The limiting oxygen index of composite materials is as high as 36.8%.However,the mechanical properties of composite materials decreases.Compared with bending properties,tensile and shear properties decreases more significantly.The tensile strength,bending strength and shear strength are 82.58MPa,161.43MPa and19.11MPa respectively.(3)Through ramie/glass fiber hybrid modification and composite material ply structure design,the mechanical properties of ramie composite materials were further improved and their moisture absorption properties were reduced.The results show that when the glass fiber content is 14wt%and in the outer layer,the mechanical properties,flame retardancy and moisture absorption of the composite material are relatively good.The tensile strength and bending strength are 102.21MPa and179.34MPa.The water absorption rate is 3.5%.The limiting oxygen index is 38.3%.There is no droplets fall during vertical combustion.The continued combustion time is 0 seconds and has a damage length of less than 1mm.The mechanical properties and flame retardant properties of the composite material meet the requirements of the composite material standard for rail transit.(4)The ABAQUS software was used to simulate and analyze the tensile and bending properties of the ramie/glass fiber composite material,which intuitively and clearly reflects the deformation of the sample under stress.It is found that the simulated values of tensile strength and bending strength are 116.91MPa,191.64MPa respectively,which is consistent with the actual test results of the composite material.The tensile stress is concentrated in the region of the specimen clamping moving end.The bending stress is concentrated in the indenter acting area.