What is the failure of mechanical parts? How many failure modes of parts?

Date：2022-03-10 13:51:46 Views：2880

The failure of mechanical parts refers to the partial or complete loss of design function during the use of parts. The parts are completely damaged and cannot continue to work; Or the parts have been seriously damaged. If you continue to work, you will lose safety; Or although it can work safely, it has lost the design accuracy and other phenomena belong to failure.

In order to prevent the failure of parts, it is necessary to analyze the failure of parts, that is, by judging the failure form of parts, determining the failure mechanism and causes of parts, selecting materials pertinently, determining reasonable processing routes, and putting forward failure prevention measures.

Main failure forms of mechanical parts

Static strength failure

When mechanical parts are subjected to external loads such as tension, compression, bending and torsion, they break or destroy because the static stress on a dangerous section exceeds the strength limit of the parts. For example, the bolt is broken after tension and the key or pin is cut or crushed.

Fatigue strength failure

Most mechanical parts work under the condition of variable stress, which can cause fatigue failure and failure.

In addition, cracks or particle spalling will also occur on the surface of parts under the long-term action of contact variable stress. Fatigue failure is a failure form that occurs gradually with the continuation of working time. It is an important reason for the failure of mechanical parts. For example, fracture caused by fatigue crack propagation, fatigue fracture and pitting of tooth root and fatigue fracture of chain after loading are typical fatigue failure. The static strength failure of mechanical parts is because the static force exceeds the yield limit, and there is often a large deformation before the fracture, so the static strength failure can be found and predicted.

Fatigue strength failure is gradually formed, but it is difficult to predict in advance, so it is more harmful.

Tribological failure

Tribological failures are mainly corrosion, wear, slipping, gluing and contact fatigue.

Corrosion is an electrochemical or chemical corrosion phenomenon that occurs on the metal surface. As a result, the surface of parts will be rusted and the fatigue resistance of parts will be reduced.

Wear is the phenomenon of loss or transfer of surface materials between two contact surfaces in the process of relative movement.

Gluing is the phenomenon that the oil film between two relatively moving surfaces is damaged, and local adhesion occurs under the working conditions of high speed and heavy load. When the two surfaces slide relatively, the bonded part is torn, and a groove mark is formed on the surface along the relative moving direction, which is called gluing.

Contact fatigue is the phenomenon of cracks or particle spalling on the surface under the long-term action of contact variable stress.

Some parts can only work normally under certain working conditions. For example, the sliding bearing with liquid friction can work normally only when the lubricating oil film of the sliding bearing is worn out. Otherwise, the sliding bearing will fail in the form of overheating, gluing and wear, which belongs to Tribological failure.

For another example, the slip of belt drive and the fretting wear of threads are also examples of tribological failure.

Other failures

In addition to the main failure modes pointed out above, there are other failure modes of mechanical parts, such as stiffness failure with excessive deformation, instability failure and so on.

In addition, the specific failure mode of mechanical parts also depends on many factors, such as the working conditions, material, loading state and the nature of stress. Even for the same part, due to different working conditions and mechanical requirements, there may be multiple failure forms. For example, gear transmission may have failure forms such as tooth fracture, wear, tooth surface fatigue pitting, gluing or plastic deformation.