The main indicators of mechanical properties of graphite materials are mechanical strength, elastic modulus, creep, and friction properties, etc.
A. The mechanical strength of graphite materials is compressive strength, flexural strength, tensile strength, etc. Mechanical strength is the ultimate resistance of materials against external damage. Compressive strength is the moment when the material is crushed under pressure. The pressure value read from the pressure gauge is the compressive strength of the graphite material. The bending strength, tensile strength and compressive strength are the same，the flexural strength is the ultimate resistance of the material when it is subjected to the breaking force and the tensile strength is the tensile force of the material.
The mechanical strength of the carbon graphite material is measured by an experimental method and its unit is Mpa (MPa). Pa is Pascal; mega is 106, which is 1000000 (one million).
1Mpa is about 10kg/cm2, which is calculated directly in our industry by 1Mpa=10kg/cm2.
The tensile strength in the mechanical strength of the carbon graphite material is about half of the flexural strength; the flexural strength is about half of the compressive strength, and the compressive strength of the artificial graphite material is 1.6-2.9 times the flexural strength, and the resistance is The tensile strength is about 0.47-0.60 of the flexural strength.
The specific strength of the carbon graphite material is moderate at normal temperature, and within 2500 ° C, its specific strength increases with increasing temperature. Therefore, carbon graphite materials have their unique advantages as high temperature materials.
B. Elastic modulus of carbon graphite material:
The modulus of elasticity is within the range of elastic deformation, and the ratio of stress to strain of the material is the modulus of elasticity, usually using Young’s modulus.
The elastic modulus is a physical quantity that characterizes the rigidity of the material. For carbon graphite materials, the elastic modulus is high as a brittle material, and the elastic modulus is low as a tough material.
Generally, the elastic modulus of carbon materials is relatively low, and the elastic modulus of graphite crystals, graphite whiskers, pyrolytic graphite, and high modulus carbon fibers is relatively high. Generally, graphite materials are basically brittle materials at room temperature and are prone to fracture.
The unit of elastic modulus is Gpa. 1Gpa = 1000Mpa.
C. creep:
Under the action of a certain pressure, the carbon material will undergo irreversible plastic deformation. This is creep. The obvious creep can be seen above 2000 °C. The carbon material has a larger creep than the graphite material, and it happens at a lower temperature. The creep of the carbon material is also directional, generally creeping parallel to the grain direction is less than the vertical direction.
D. the friction properties of graphite materials:
The graphite material has the advantages of both wear resistance and lubricity. This is because the graphite crystal is easily peeled off along the crystal layer direction, and a very thin graphite crystal film is formed on the friction surface, so that the friction coefficient is remarkably lowered, which is the reason for why the graphite material is self-lubricating. The self-lubricity of graphite depends on the presence of water and air. When the moisture content in the working environment is less than 5 g/cm3, the wear rate of graphite increases. In the air at a temperature of 300-400 ° C, the friction coefficient is increased due to strong oxidation of graphite, and in the neutral and reducing medium, good wear resistance can be maintained even at a temperature of 300-1000 ° C.
