Jiming Zhou

Effect of specific pressure on fabrication of 2D-Cf/Al composite by vacuum and pressure infiltration

Abstract Carbon fiber reinforced aluminum matrix (Cf/Al) composite has many excellent properties, and it has received more and more attention. Two-dimensional (2D) Cf/Al composites were fabricated by vacuum and pressure infiltration, which was an integrated technique and could provide high vacuum and high infiltration pressure. The effect of specific pressure on the infiltration quality of the obtained composites was comparatively evaluated through microstructure observation. The experimental results show that satisfied Cf/Al composites could be fabricated at the specific pressure of 75 MPa. In this case, the preform was infiltrated much more completely by aluminum alloy liquid, and the residual porosity was seldom found. It is found that the ultimate tensile strength of the obtained Cf/Al composite reached maximum at the specific pressure of 75 MPa, which was improved by 138.9% compared with that of matrix alloy.

Threshold pressure and infiltration behavior of liquid metal into fibrous preform

A dynamic measuring apparatus was developed to investigate the infiltration process of liquid metal into the fibrous preform. 10% (volume fraction) chopped carbon fiber preforms were infiltrated with magnesium alloy under different infiltration pressures. The threshold pressure and flow behavior of liquid metal infiltrating into the preforms were calculated and measured. The microstructure of obtained Cf/Mg composites was observed. The results indicate that the measured threshold pressure for infiltration was 0.048 MPa, which was larger than the calculated value. The infiltration rate increased with the increase of infiltration pressure, but the increase amplitude decreased gradually. The tiny pores in the composites could be eliminated by increasing the infiltration pressure. When the infiltration pressure rose to 0.6 MPa, high quality Cf/Mg composite was obtained.

Influence of Notch on Mechanical Properties of Cf/Mg Composite Fabricated by LSEVI

Cf/Mg composite was fabricated by liquid-solid extrusion following vacuum infiltration technique and uniaxial tensile tests were conducted on the notched and unnotched specimens to investigate the mechanical properties of Cf/Mg composite. The effects of circular notch on the notched strength, net tensile strength, tensile modulus, and fracture strain of Cf/Mg composite were investigated. The notch sensitivity of Cf/Mg composite was elucidated through the notch strength ratio (NSR), fracture surface, and fracture mechanism. By comparing the experimental and theoretical NSR, the influences of notch size and stress concentration factor on notch sensitivity of Cf/Mg composite were investigated. The results showed that the fracture strain of the notched specimens increased with increasing the notch size. Meanwhile, net tensile strength, notched strength, and tensile moduli had opposite trends. The NSR had a functional relationship with the notch size and stress concentration factor caused by the notch had no influence on the NSR.

Principal strain-induced fiber orientation evolution in the Csf/Mg composites with a large deformation

In this article, the fiber orientation evolution in the Csf/Mg composites with a large deformation is investigated. The principal strain-induced fiber orientation evolution mechanism, which states that the fiber orientation evolution in the Csf/Mg composites with a large deformation is determined by the principal strains, is proposed. The fiber orientation distribution factors F i ( i = 1 ,   2 and 3 ) taking the form of the principal strains are proposed to quantitatively characterize the fiber orientation distribution in the Csf/Mg composites. The fiber orientation factors F i s predicted by the finite element simulation based on the principal strain-induced fiber orientation evolution mechanism are compared against those F i m measured from the micrographs of the extrusion experiments of Csf/Mg composites. The results demonstrate that the principal strain-induced fiber orientation evolution mechanism is valid and convenient to predict the fiber orientation evolution in the Csf/Mg composites with a large deformation. In the extruded Csf/Mg composites, the fibers are reoriented toward the direction of the maximum principal strain and deviated from the direction of the minimum principal strain.

Liquid-Solid Forming under High Pressure

1School of Mechanical Engineering, Northwestern Polytechnical University, Xi’an 710072, China 2Mechanics, Materials and Structures Research Division, Faculty of Engineering, University of Nottingham, Nottingham NG7 2RD, UK 3School of Materials and Metallurgy, Northeastern University, Shenyang 110819, China 4School of Material Science and Engineering, Harbin Institute of Technology, Harbin 150001, China

Numerical Simulation of Liquid-Solid Extrusion Process Based on the Mechanical Model Coupled with Solidification

Liquid-solid extrusion process is a combined process of casting and extrusion which can be used to form tubes or bars directly from liquid metal. The performance of products is enhanced through the large deformation and the solidification under pressure with less shrinkage cavity or porosity. Numerical simulation of this process is hard to run for it involves mechanical modeling of the dynamic transition from liquid phase to solid phase. The liquid zone and solid zone were modeled independently for reasons of their different characteristics of deformation. The deformation of liquid zone was described according to the principle of element removal method which eliminates the elemental distortion during the simulation. The solidified zone under elevated temperature was modeled through the hyperbolic sine constitutive equation. The dynamic transitions from liquid phase to solid phase were determined based on the results of thermal analysis. The mechanical model coupled with solidification proposed in this paper was verified through the experiments of liquid-solid extrusion of LY12 alloy.