| In recent years,our country has actively promoted energy conservation and emission reduction in the automotive industry,so many auto companies have vigorously carried out lightweighting of auto parts to meet national environmental protection policies.Carbon fiber composites have the characteristics of light weight and high strength,and are gradually used in the manufacture of automobile parts.As the structure and rotating parts below the spring,the weight reduction effect of the drive shaft is more obvious than the body.So the research and application of high-performance carbon fiber composite transmission shaft has great significance to the lightweight of automobiles.The transmission shaft is next to the exhaust pipe in the arrangement of the chassis and is at a relatively high temperature for a long time.In addition,the car may also be used in harsh environments such as high temperature?such as desert areas?,high humidity and heat?coastal areas near the equator?,so the research on the characteristics of hygrothermal aging and thermo-oxidative aging of composite transmission shafts has very great significance in application.This paper selected carbon fiber reinforced heat-resistant resin composite used in a certain carbon fiber composite drive shaft as the research object.The hygrothermal aging and thermo-oxidative aging behavior of the composites were systematically studied,which provided key data for the use conditions of this transmission shaft.The specific methods and conclusions of this study are as follows:?1?Differential scanning calorimeter has been adopted to characterize the curing characteristics of HY-230 resin and determine the curing plan.The final plan is to cure at 140?for 40 min.The composite laminates with different thicknesses were prepared by VARI molding process and their static mechanical properties,heat resistance and cross-sectional morphology were characterized.The results showed that the laminate had excellent and stable mechanical properties,tight bonding between fibers and resin,and good interface properties.?2?The effect of hygrothermal aging on the performance of composites.Put the tensile,compression,bending,shearing and other test specimens of the composite into 40?and 60?water bath?100%humidity?for 60 days.Took out the samples regularly,and tested the sample for water absorption and diffusion,mechanical and thermodynamic properties.Under the hot water immersion at 40?,the composite reached the moisture absorption equilibrium after 400 hours of water immersion.The diffusion coefficient of water in this composite is 1.919×10-3 mm2/h.Under the hot water immersion at 60?,the composite reached the moisture absorption equilibrium after170 hours of water immersion.The diffusion coefficient of water in this composite is 4.626×10-3mm2/h.The results showed that the higher the temperature,the faster the diffusion rate of moisture in the composites.After 60 days of aging at 40?water bath,the retention rate of the tensile,compression and bending mechanical properties of the composite was above 87%,and the retention rate of interlayer shear strength was 82%.The SEM test result showed that after 60 days of aging under 40?water bath,the tensile cross-section of the composite was not flat and less resin was attached to the fiber surface,but the fiber/resin interface performance remained good.However,after 60 days of aging at 60?water bath,the retention rate of tensile,compression and bending mechanical properties of the composite was above 83%,and the retention rate of interlayer shear strength was 70%.The SEM test results showed that after 60 days of aging under60?water bath,the resin fell off more,the matrix was cracked,and the fiber/resin interface bonding performance was problematic.The DMA test results showed that the glass transition temperature of the composite did not change much after aging at 40?and 60?water bath for 60days.Infrared spectrum analysis of HY-230 resin showed that the composite undergoed almost no chemical changes after hygrothermal aging in the water bath.Based on the above tests,it is concluded that the composite can be used for a long time in the humid environment of 40?,but the use temperature should not exceed 60?.?3?The effect of thermo-oxidative aging on the performance of composites.Put the composite test strips in the oven at 140?and 200?for 60 days,and took them out regularly to characterize the mechanical and thermodynamic properties of the samples.After aging at 140?for 60 days,the retention rate of the tensile,compression,bending and interlayer shear strength of the composite was above 87%.The SEM test results showed that after 60 days of high temperature aging at 140?,the tensile fracture was uneven,the resin matrix was cracked,and the interface was slightly debonded.However,after aging at 200?for 60 days,the tensile,compression,bending and shear strength retention rate of the composite decreased seriously,of which the shear strength decreased the most,with a drop of 82%.The SEM test results showed that the fiber bundle distribution was divergent,and the fibers were almost in the form of single roots.The fiber surface was smooth and the fiber/resin interface damage was serious.The DMA test showed that the glass transition temperature of the composite aging at 140?for 60 days increased to 192?,and after 60 days at 200?,the glass transition temperature of the composite dropped to 151?.The infrared spectrum analysis of HY-230 resin showed that in the thermo-oxidative aging environment for a long time,the oxygen will react with the resin matrix faster and generate more carbonyl groups.Based on the above tests,it is concluded that the maximum operating temperature of the composite is around 140?. |
PDF Full Text Request