Influence Factors Of Retention Length Of Carbon Fiber On The Properties Of PA66

With the development of material technology,carbon fiber reinforced modified materials have been widely used in aerospace,high-speed rail,electronics,new energy vehicles and other fields.Carbon fiber is the main bearing body of load in composite materials.Generally,the retention length of carbon fiber in composite materials directly affects the stress transfer in materials,which is a core factor for the excellent performance of materials.Therefore,it is of great significance to improve the comprehensive properties of the composites by using different conditions to improve the fiber retention length of the carbon fiber reinforced materials.This paper studies the influence of different processing equipment,screw combination and processing conditions on the retention length of carbon fiber.The carbon fiber retention length,probability distribution and micro morphology of the composite under various equipment and process conditions were studied by means of secondary optical display,scanning electron microscope(SEM),Leica optical microscope and instrumented impact.The influence of these factors on the mechanical properties of reinforced polyamide 66(PA66)was analyzed,and the internal relationship between these differences and the macroscopic properties of the material was discussed.The following results were obtained:1.In the condition of single screw extruder,the retention length of carbon fiber is 1.3 times as long as that of twin screw extruder,and the average length is 0.18 mm.However,in the condition of single screw extruder,the dispersion and infiltration effect of carbon fiber is worse,resulting in a large number of stress concentration defects in the material,and the average performance of the material is 25% lower than that of twin screw extruder.2.The combination of twin-screw with weak shear can improve the retention length of carbon fiber,which is mainly due to the fact that the weak shear screw reduces the external shear and the self shear of carbon fiber at the same time.The higher the proportion of carbon fiber is,the more obvious the self shear effect is.When the content of carbon fiber is 30% ～ 40%,the self shear of fiber has played a major role in the damage of fiber length.The retention length of carbon fiber can be increased by 17% by using the tooth disk element,and the material properties can reach the level of 40% carbon fiber content without adjusting the screw when the carbon fiber content is 30%.3.The influence of the retention length of carbon fiber on the properties of the material after moisture absorption is studied.It is found that longer retention length of carbon fiber is beneficial to the improvement of the absolute value of the material properties after moisture absorption,and higher content of carbon fiber is beneficial to the improvement of the performance retention rate of the composite after moisture absorption.4.The adjustment of processing technology can effectively reduce the self shear effect of carbon fiber,and the screw speed is the most important factor.When the screw speed increases from 100 r / min to 500 r / min,the retention length of carbon fiber decreases by 46%.The fiber retention length at 100 r / min is 23% higher than that at 300 r / min,and the tensile and bending strength of the composite increases by 8% ～ 10%.At the same time,the instrumented impact study found that the longer the retention length of carbon fiber is conducive to the increase of the maximum impact force Fmax,the crack initiation force FS and the impact displacement SM at the same time.Compared with 300 r / min,the values of Fmax and FS at 100 r / min are increased by 6.5% and 10% respectively.