Damage Study And Fabrication Technology Of C_f/Mg Composite Part By Liquid-solid Extrusion Following Vacuum Infiltration Technique

Magnesium alloy is a distinctive lightweight metal due to its extraordinary low density.Unfortunately,its utilization is often restricted since Mg alloy suffers from several material inherent deficiencies like low stiffness,low fatigue resistance,high thermal expansion coefficient,etc.Carbon fiber reinforced magnesium composite(C_f/Mg composite)which holds a lot of outstanding merits because of the combination of material capability of carbon fibers and Mg matrix,including low density and thermal expansion coefficient,high specific stiffness and strength and so on.Thus this composite has great potential as replacement for traditional structural materials.Although the preparation process and performance improvement of C_f/Mg composites have been studied,the research on damage and structural component preparation is still limited.So,study on the damage mechanism and component preparation can be used to provide experimental data support for structure design,overload and fatigue safety design,damage finite element simulation and so on,and it also makes technical reserve for the popularization and application of this kind of composite material.In this paper,the research on damage and structural component preparation is as the research object.C_f/Mg composite fabricated by LSEVI technique,progressive damage,fatigue damage and notch damage are the ultimate goal of the research.The main research contents are as follows.(1)The effect of fiber architecture on C_f/Mg composites was studied.Four kinds of Cf/Mg composites with different fiber architectures were tested,and the microstructure and fracture surfaces were examined by SEM.The influence of fiber architecture on tensile and compressive properties of C_f/Mg composites was investigated.The composite with non-woven carbon fiber fabric perform(NWFP)had the highest properties.The ultimate tensile strength is 385 MPa and the elasticity modulus is 71 GPa,which increase 180%and 86%compare with that of the matrix AZ91D alloy.The compressive strength in XY direction which is improved by 110%compared with the matrix.Based on the experimental observations and analysis the failure mechanism of C_f/Mg composite was proposed.(2)The progressive damage of C_f/Mg composite was studied.Monotonic loading and stepwise loading tensile test were carried out to analyze the mechanical properties.Fracture morphology and SEM micrographs were examined to understand the damage mechanism and progressive failure of C_f/Mg composite.Two major damage processes were observed,one is between 90-150 MPa,the other is between 240-300 MPa.These phenomena can be attributed to the facts that the matrix alloy lose its bearing capacity,and the fiber damage.(3)The tensile and fatigue behavior of C_f/Mg composites was investigated experimentally.The S-N curve of the composite was determined and the fatigue behavior considering different loading levels and cycles was studied.The fatigue limit of C_f/Mg was determined to between250-270 MPa about 65%-70%of the ultimate tensile strength.Moreover,the fracture surfaces and microstructures of test samples were examined to understand the fatigue damage mechanism.The investigation finds that the residual tensile strength of specimens that survived during fatigue test was enhanced with the increase in fatigue cycles and applied stress.In addition,fatigue loading could change the tensile behavior of the composite,and a yielding point was observed at stress-strain curves of specimens which survived during fatigue test.Observations of the fracture surfaces revealed that more fibers were pulled out with the increase in fatigue cycles and applied stress.(4)The notch damage of C_f/Mg composite was studied.The influence of notch size on the tensile properties of C_f/Mg composite was analyzed.The notch sensitivity of C_f/Mg composite was elucidated through the notch strength ratio(NSR),fracture surface and fracture mechanism.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.(5)The analysis and testing of the C_f/Mg composite plate component was carried out.The C_f/Mg composite can replace the metal material and meet the requirements of the shape and structure of the plate component.The blank design,forming scheme and preparation process are studied and the technical bottleneck and technical difficulties in the fabrication of C_f/Mg composite plate are solved.C_f/Mg composite plate component without the obvious macroscopic defects were prepared by LSEVI.The test showed that the mechanical property,and overall bearing capacity of C_f/Mg composite plate component were better than that of the AZ91D alloy.