Finite Element Simulation Of HP Process Of SiC_f/TC17 Composite Sheet

Continuous Si C fibers reinforced Ti-based composites(TMCs)is a new material that combines plasticity and formability of the matrix Ti alloy with the load-bearing capacity and rigidity of the reinforced Si C fibers,whose specific strength,specific stiffness,high temperature strength and creep resistance are superior to traditional Ti alloys,also can maintain excellent fatigue resistance and creep resistance at thehigh temperature,so they have a broad application prospect in the aerospace field.In this paper,Abaqus finite element analysis software was used to numerically simulate the densification and thermal residual stress of Si C_f/TC17 composite during hot pressing(HP).According to the periodic arrangement and symmetry of the fibers,a finite element model under plane strain condition was established.When the Si C_f/TC17 composite sheet was prepared by hot pressing with the coating method,the relationship between the density in the HP process and the HP time was four stages:slow densification stage,accelerated densification stage,rapid densification stage and deceleration densification stage;in the early stage of HP,the density of the square arrangement is significantly less than that of the hexagonal arrangement;in the later period of HP,the density increases rate of the square arrangement is significantly higher than hexagonal arrangement.The density of the HP square arrangement and the hexagonal arrangement tend to be the same in the final stage;if the goal is to achieve complete densification,the effect of the two fiber arrangements is basically the same.In the early stage of HP,increasing the fiber volume fraction can slightly increase the density of the preform;in the later stage of HP,increasing the fiber volume fraction can slightly decrease the density of the preform.Increasing the heating rate can significantly shorten the time for complete densification of the composite;increasing the pressure increase rate can appropriately increase the density of the composite.In addition,the thermal residual stress of the Si C_f/TC17 composite was numerically simulated,the effects of the type and thickness of the fiber surface coating and the fiber volume fraction on the thermal residual stress were analyzed.The results show that different fiber surface coating types have a greater impact on the radial thermal residual stress inside the fiber,and have little effect on radial thermal residual stress of the surface coating and the Ti alloy matrix;the surface coating type has a great influence on the surface coating loop thermal residual stress and has little effect on the internal thermal residual stress of the fiber and the Ti alloy matrix.The Gd surface coating is the best fiber surface coating from the perspective of stress gradient.Different fiber surface coating thickness has little effect on the radial and hoop thermal residual stress of the composite;as the thickness of the fiber coating increases,the radial and hoop thermal residual stress gradient in the composite decreases accordingly.The higher the fiber volume fraction,the smaller the radial thermal residual compressive stress inside the fiber and Ti alloy matrix,the smaller the hoop thermal residual compressive stress inside the fiber,and the greater the hoop thermal residual compressive stress inside the Ti alloy matrix;The hoop thermal residual stress gradient inside the Ti alloy matrix is inversely related to the fiber volume fraction;as the fiber volume fraction increases,the stress gradient in the composite material also decreases.