Preparation Of Ramie Reinforced Composite Modified By Shear Thickening Fluid And Its Impact Resistance

In recent years,the rapid development of high-technology,more and more composite materials have been used widely.However,with the reduction of fossil resources such as oil and human environmental awareness,new biodegradable environmentally friendly composite materials has become the focus of attention.Natural fiber-reinforced composite materials are widely used in automobiles,from the past used in automotive interior decoration gradually applied to automotive exterior parts,and has begun to try to use in the automotive structural carriers.Therefore,it is necessary for natural fiber reinforced composite materials to have good mechanical properties such as stretching,bending,impact and so on.And so,the mechanical properties of ramie-reinforced polylactic acid composites are studied in this paper,which provides some theoretical support and reference for the application of natural fiber-reinforced composites in automobile field.Based on the previous research,the Ramie fabric was used as the reinforcement,the polylactic acid as the resin matrix.The surface of the ramie fabric was treated by alkali treatment,silane coupling agent(KH550)treatment,alternating treatment and plasma modified treatment;.The composite process of preparation and optimization of the shear thickening liquid-ramie fabric was studied.The composites with different angles and different thicknesses were designed.Ramie reinforced polylactic acid composites were prepared by optimizing the molding process.The mechanical properties and the impact resistance were tested.The following conclusions can be drawn.(1)There is no new characteristic absorption peak in the spectrum of shear thickening liquid.The shear thickening liquid is a stable system without chemical reaction.When the ramie fabric and STF composite,ramie fiber is evenly coated by SiO2.Ramie fabric surface was attached and filled by a large number of SiO2 particles.With the increase of STF concentration,the weight gain and thickness of STF-ramie composite fabric increased.Thickness increase effect is notobvious,and composite fabric permeability decreased.(2)The interweaving resistance of the ramie fabric was increased with the increase of the concentration after the impregnation of STF,and there was a positive correlation between the two.Compared with the original sample,the breaking strength of the composite fabric increases,the elongation at break decreases,and the breaking strength increases with the concentration of impregnation treatment.In the low-speed tensile conditions,the fracture strength growth is slow.In the high-speed tensile conditions,it increases the effect is obvious.Shear thickening resistance to rapid tensile deformation effect is obvious.When the concentration of immersion treatment,the more filled SiO2 particles,the effect is more obvious.(3)Using the orthogonal test method,the L9(34)orthogonal table was selected.The range analysis method was used to evaluate the mechanical properties,and the surface and cross-sectional morphology of the composites were analyzed.The optimum molding parameters were determined to be 170?,7MPa and 40 min respectively.After adding the gasket in the mold,the surface morphology of the composites is improved to a higher degree.Therefore,the need for composite material preparation requirements to select the appropriate thickness of the gasket.(4)The tensile and flexural properties of the composites were compared and analyzed.It was found that the tensile and flexural properties of the composites prepared by 5wt% alkali +5wt% KH550 were the best.Tensile fracture mode is ductile fracture.(5)Impact resistance:When the concentration of KH550 was 5%,the pressure was 30 Pa,the power was 120 W,and the plasma treatment time was 4min,the impact properties of the prepared composites were the highest excellent.When the concentration is 5wt% alkali + 5wt% KH550,the impact toughness of the composites is increased by 54.4KJ.m-2 respectively under the multi-factor alternating treatment.The impact toughness of the composites was improved obviously when compared with the single factor treated ramie fabrics.The impact toughness of the composites increased with the increase of the STF concentration,but the impact toughness of the composites increased first and then decreased with the shear thickening and impregnation treatment.(6)In the thickness direction,the impact toughness of composites increased with the increase of ramie fabric reinforcement layer.The impact toughness of the composites was H2>H5> H1> H4> H3.The impact angle of 30°on the impact resistance of composite materials to improve the effect is more obvious.(7)The energy absorption mechanism of the two-layer composite material can be divided into three processes: firstly,the hammerhead contact surface composite material is mainly shear failure of the fiber reinforcement.As the pendulum hammer through the layer by layer,the middle part of the main form of reinforced fiber reinforced plastic shearing failure,the main form of damage to the tensile fracture,hammer contact with the back of the fiber reinforced tensile fracture failure.