Mechanical Properties And Numerical Simulation Of SiC Nanowire Reinforced Aluminum Matrix Composites

The property of Aluminum matrix composites depends on the matrix and the reinforcement.SiC with lots of advantages,such as high strength,high hardness,good wear resistance,small thermal expansion coefficient,good thermal stability etc.,have been widely used as reinforcement in the Al matrix composites.Well,the intrinsic brittleness and poor toughness is its limitation.SiC nanowires not only keep the advantages of SiC particles,but also have much higher strength and toughness than SiC particles and SiC whiskers.So,if SiC nanowires were used as reinforcement in the Al alloys,it would be obtained a higher reinforcement efficiency,and the Al composites with better performance.In order to study the basic rules of strengthening of aluminum and aluminum alloy matrix by nano-reinforcements with a view to obtaining high-strength composites,SiCnw/Al composites were successfully prepared by pressure infiltration method using SiC nanowires as reinforcement and four aluminum alloys of different strength grades1A99,2024,6061 and 7075 as matrix,and the effects of volume fraction of SiC nanowires,arrangement mode,matrix strength and heat treatment state on the mechanical behavior and strengthening effect of SiCnw/Al were investigated.It was shown that the SiCnw/Al composites made by using pressure infiltration method had good interfacial bonding and without interfacial reaction.SiC nanowires were uniformly distributed in the matrix.Some few pores could be eliminated by hot extrusion,the density reaches 99.9 % by hot extrusion in the two-phase region of the matrix alloy.More than 95% of the SiC nanowires in the SiCnw/Al composite after hot extrusion deformation were oriented in the axial [111] crystal direction along the extrusion direction,and the P parameter of the specimen perpendicular to the extrusion direction was close to1,while the P parameter parallel to the extrusion direction was only about 0.03.The results demonstrated that when the volume fraction of SiC nanowires increased,the interfering interweaving between SiC nanowires during extrusion and deformation led to an increase in the fracture tendency of SiC nanowires.The average length of SiC nanowires decreased from the original 10-50 μm to 9.2 μm,8.7 μm and 7.9 μm for the three volume fractions(10 %,15 % and 20 %)of SiCnw/6061 Al composites after extrusion,respectively.The highest strengthening factor f and strengthening efficiency R among all SiC-reinforced aluminum matrix composites,with the highest strengthening factor of 283% and the highest strengthening efficiency of 12.The fractures of SiCnw/Al composites showed brittle fractures in all macroscopic aspects.Microscopically,there appeared a large number of tough nests and also some destructive steps with both brittle fracture and plastic fracture.The SiC nanowires fracture in the composites in three types of ways,direct fracture,pulling out from the matrix,or debonding.The fracture of SiC nanowires in cast composites was dominated by pulling out from the matrix and debonding from the matrix,and after hot extrusion,the fracture of composites was mainly a direct fracture of SiC nanowires.In the numerical simulation,the matrix employed a linear strengthening intrinsic model,which accurately simulated the real stress-strain response of the matrix during large deformation;the matrix fracture simulation used the Bao-Wierzbicki damage criterion,which accurately simulated the elastic/plastic strain and fracture process of the matrix by considering the damage factor to measure the strength and stiffness degradation of the material during the damage process through the ductile damage theory,and the simulation data matched with the real test situation.The fracture simulations were validated by using Griffith’s strength criterion and the stiffness degradation after damage;the fracture process of SiC nanowires was accurately simulated by using Griffith’s strength criterion and the stiffness degradation after damage;and provided a theoretical basis for the design of SiCnw/Al composites.The microscale RVE model of three-dimensional SiCnw/Al composites was established,and the intrinsic model that could accurately simulate the stiffness and strength of SiCnw/Al composites was found.Compared with the mixed-law model(ROM),Cox model,and Jiang model,the Halpin-Tsai model could more accurately simulate the elastic modulus of SiCnw/Al composites,and the Shin-modified shear-lag model could more accurately simulate the yield strength of the composites.In this study,according to the good Strong and toughening characteristics of SiC nanowires reinforced Al,SiC nanowires were further incorporated into the interlayer of Cf/Al composites.SiC nanowires could effectively improve the interlayer shear strength of Cf/Al composites and the bending strength of Cf/Al composites.The prepared precision base of a flight vehicle has improved the accuracy by nearly 2 times under vibration and impact loading.