Study On Mechanical Properties And Foaming Behavior Of Carbon Fiber Reinforced Nylon 6 Composites

The use of engineering plastics or carbon fiber（CF）reinforced engineering plastics composites instead of traditional automotive metal materials is an important development direction of automotive lightweight.Among engineering plastics,nylon6（PA6）has attracted much attention in the field of automotive lightweight due to its excellent combination performance with CF.However,because continuous CF and nylon are difficult to form a variety of complex shape products,therefore,a lot of research has been done on short-cut CF reinforced nylon composites.At present,there are few studies on mechanical properties of short-cut carbon fiber（SCF）reinforced PA6 composites and foaming behavior of CF/PA6 composites.Herein,this paper has important scientific significance and application value for the recycling and reuse of SCF/PA6 composites and related research on the lightweight of CF/PA6 foamed composites.Under the above research background,a series of researches on mechanical properties,foaming behavior and mechanical properties of SCF/PA6composites were carried out in this paper,aiming at SCF reinforced PA6 as the research object.The main contents are as follows:（1）The CF/PA6 unidirectional strips with different lengths were fabricated into laminates by hot pressing,and their mechanical properties and interfacial bonding properties were tested.The influence of CF unidirectional strip length on mechanical properties of SCF/PA6 composites was studied,and the strengthening mechanism of SCF/PA6 composites with different unidirectional strip length was analyzed.Experimental results show that tensile strength,modulus and elongation at break of CF/PA6 composites show an increasing trend.Tensile strength,modulus and elongation at break of the 24 mm specimen increased by 72.48%,15.16%and 52.25%respectively.Bending strength and modulus increased by 83.72%and 18.69%respectively as the length of CF/PA6 unidirectional strip in the test spline increases from 6 mm to 24 mm,tensile and bending fracture morphology and fracture mechanism of short-cut CF unidirectional strip laminates with different lengths were described,and the optimum length of short-cut CF unidirectional strip was obtained by comparison.（2）PA6 foaming materials with different cellular structures were prepared by two-step foaming method.The influence of foaming temperature and pressure on cellular size and density was studied,and the compressive properties of PA6 foaming materials were tested.Experimental results show that when the pressure of the foaming reactor is constant and the temperature rises from 200℃to 205℃,the average size of the bubbles increases and the density of the bubbles decreases.When the temperature rises from 205℃to 210℃,bubbles average size decreases,while the change of the density of the bubbles is opposite.PA6 crystallinity increased from 67.73%to 74.62%after foaming.When the temperature increases from 200℃to 205℃,PA6 foam material compressive strength decreases rapidly.When the temperature increases from 205℃to 210℃,the compressive strength of PA6 is slightly higher than that of 205℃.In this chapter,the basic law between sc CO₂ foaming process conditions and microstructure of PA6 was established.（3）Based on the foaming process of pure PA6 material,CF/PA6 composites with different CF content were prepared,and their foaming behavior was studied:the effect of CF content on the size and density of CF/PA6 foam material was studied,and the mechanical properties of CF/PA6 foam material were tested.Experimental results show that with the increase of CF content from 0 to 2%,bubbles average size decreases and the density of bubbles increases,and the compression strength required to reach the preset strain of 30%increases from 1.7 MPa to 15 MPa in the compression experiment.Conclusion of this chapter reveals the heterogeneous nucleation of short-cut CF in the foaming process of PA6,and its effect on the structure of bubbles,and explains the reason why the compression properties of CF/PA6 foaming materials are significantly improved.