The strength of the chain can reflect the ability of the chain to resist fracture, transition deformation and damage under the action of external force, while the hardness of the chain can reflect the resistance of the chain to wear, so do you know how the strength and hardness values are obtained?

STRENGTH

Strength refers to the ability of a material to resist fracture, excessive deformation and destruction under the action of external force. It expresses a degree that is often used as the value of the force or energy needed to reach an adverse state. The corresponding values and names of different cases are different, including the common compressive strength, tensile strength, yield strength and so on.

Compressive Strength

Compressive strength is the ability of a material to resist damage when under pressure, usually expressed by the maximum pressure it can withstand per unit area.

test method

The pressure test machine is generally used for testing.

During the compressive strength test, it is necessary to place the material of the standard specimen size (150mm 150mm 150mm) between the upper and lower plates of the pressure plate of the pressure tester to ensure that the pressure surface of the specimen is in full contact with the pressure plate, and the axis of the specimen coincides with the loading axis of the pressure tester to avoid eccentric loading.

Open the pressure test machine and apply pressure on the specimen at a certain loading rate. During loading, the pressure testing machine automatically records the pressure and the deformation of the specimen.

When the specimen is crushed (with obvious signs of crack, breakage, etc.), record the maximum pressure value FN at this time and introduce the formula:

Where: A = 150 x 150 = 22,500 mm ²

The compressive strength of the material can be calculated.

Tensile Strength

Tensile strength is the maximum stress value of the material resisting fracture under tensile load.

test method

Universal material testing machine is generally used for testing.The range of the test machine shall be selected according to the expected tensile strength of the material and the cross-sectional area of the sample to ensure the accuracy of the tension measurement during the test.

Yield Strength

For metal materials, when the stress of the material reaches the yield strength, the material will produce obvious plastic deformation. On the stress-strain curve, it is the stress value corresponding to the turning point of the material to transition from the elastic deformation stage to the plastic deformation stage.

test method

For metal materials, tensile experiment method is mainly used, while for brittle materials or materials under specific circumstances, compression experiment method is used.

Tensile experiment generally uses a universal material testing machine.

In the experiment, the test machine synchronously records the tension and the elongation data of the sample, which can generate the force-displacement curve or stress-strain curve, so as to determine the strength of the area.

The compression test method usually uses the pressure test machine.

At the time of the experiment, a compressive load was applied at the appropriate loading rate while load-displacement data were recorded. When the obvious turning point appears in the load-displacement curve, that is, the material changes from elastic deformation to plastic deformation, the corresponding stress value (obtained by dividing the load divided by the cross-sectional area of the sample) can be used as a reference for the yield strength.

HARDNESS

Hardness refers to the ability of the material to locally resist the hard object pressure into its surface. Generally, the higher the hardness, the stronger its wear resistance type, so the hardness can reflect the anti-wear ability of the chain.

According to different test methods, there are brinell hardness, Roche hardness, Vickers hardness, Richkell hardness and other different expressions, among which BU and Rockell are more commonly used.

Brinell Hardness

It is through the diameter of a certain diameter of hard alloy ball or quenching steel ball, under the pressure of the measured material surface under the action of the specified test force, maintain the specified time, measure the indentation diameter to calculate the hardness value.

merit

The indentation area of the Brinell hardness test is large, which can reflect the average performance of the comprehensive influence of each component in a large range of materials, regardless of the individual composition phase and small inhomogeneity.

shortcoming

The Brinell hardness test operation is relatively complex, and the test efficiency is low. Moreover, due to the large indentation, it is not suitable for the hardness test of finished products and sheet material, because it will cause great damage to the test sample and affect its performance.

Brinell Hardness

It calculates the hardness value by using a diamond cone with a top angle of 120 or a quenching steel ball with a diameter of 1.588mm as the pressure head. Under the action of the initial test force and the main test force, the pressure head is pressed into the surface of the tested material, then the main test force is removed, and the residual increment of the indentation depth is measured under the initial test force.

merit

Rockwell hardness test is easy and quick, you can read the hardness value from the hardness gauge dial directly. The test efficiency is high, and because the indentation is small, the surface damage of the workpiece is small, which is suitable for the hardness test of finished products and thin workpiece.

shortcoming

Due to the small indentation, the representation may be inferior to Brinell hardness, and for the material organization is not uniform, the measurement results may be greatly biased. In addition, the hardness values between different scales cannot be directly compared, and they need to be converted.