What's the difference between stiffness, strength and hardness?
Stiffness: refers to the ability of a material or structure to resist elastic deformation when stressed. It is a manifestation of the difficulty in elastic deformation of materials or structures. The stiffness of materials is usually measured by the elastic modulus E. In the macroscopic elastic range, the stiffness is the proportional coefficient that the load of parts is directly proportional to the displacement, that is, the force required to cause unit displacement.
Hardness: the ability of a material to locally resist hard objects from pressing into its surface is called hardness. The local resistance of solids to foreign invasion is an index to compare the hardness of various materials.
Strength: one of the mechanical properties of engineering materials to resist fracture and excessive deformation. The commonly used strength performance indexes are tensile strength and yield strength (or yield point). Cast iron and inorganic materials will not yield, so their strength characteristics can only be measured by tensile strength. Polymer materials also adopt tensile strength. When subjected to bending load, compression load or torsion load, the strength performance of a material should be expressed by its bending strength, compression strength and shear strength.
Extended data indentation hardness
Press the specified indenter into the measured material with a certain load, and compare the hardness of the measured material according to the degree of local plastic deformation on the surface of the material. The harder the material, the smaller the plastic deformation. Indentation hardness is widely used in engineering technology. There are many kinds of indenters, such as steel balls, diamond cones and diamond pyramids with a certain diameter.
The load varies from a few grams of force to several tons of force (that is, tens of millinewtons to tens of thousands of newtons). Indentation hardness also defines the duration of load acting on the surface of the measured material. The main indentation hardness is Brinell hardness, Rockwell hardness, Vickers hardness and microhardness.
Roche hardness
This hardness test method was put forward by S.P. Lakwer of the United States in 19 19, which basically overcame the above shortcomings of Brinell test method. The indenter used for Rockwell hardness is a diamond cone with a cone angle of 120 or a steel ball with a diameter of 116 inch (1inch is equal to 25.4 mm), and the indentation depth is used as the basis for calibrating the hardness value.
When measuring, the total load is divided into initial load and main load (total load minus initial load). The initial load is generally 10 kg. After adding to the total load, the main load is removed, and the indentation depth at this time is used to measure the hardness of the material.
References:
Baidu Encyclopedia: Hardness
Baidu Encyclopedia: Strength
Baidu encyclopedia: stiff