3 Main Failure Modes Of Mechanical Machined Parts

Mechanical parts cannot perform normal functions within the period reserved by the design scheme and under the required standards. Failure forms of mechanical parts: overall fracture, plastic deformation, erosion, wear, gluing and contact fatigue. Evaluation criteria for mechanical parts in general design scheme: static compressive strength, fatigue limit, friction and wear.

1. Static Compressive Strength Failure

When mechanical parts are subjected to external loads such as bending, compression, bending and torsion, they will crack or be destroyed because the static stress on a dangerous section exceeds the yield limit of the parts. For example, the anchor bolt is broken after bending and the key or pin is broken or crushed.

In addition, if the stress on the part exceeds the strength limit of the raw material, the part will undergo plastic deformation. Plastic deformation will lead to the reduction of precision or inaccurate positioning, seriously endangering the normal work of parts, so it is also classified as failure.

2. Fatigue Limit Failure

The vast majority of mechanical parts operate under the variable stress standard, and the function of variable stress can cause fatigue damage of parts and lead to failure.

In addition, cracks or particle shedding may occur on the surface of the part under the long-term effect of touch stress. Fatigue failure is a failure form that occurs slowly with the running time, and it is the key reason for the failure of mechanical parts.

For example, after the axle is loaded, fatigue crack propagation causes cracking, fatigue fracture and crevice corrosion of gear teeth and fatigue fracture of drive chain are very typical fatigue failures. The failure of the static compressive strength of mechanical parts is due to the fact that the pile exceeds the strength limit and usually undergoes very large deformation before cracking, so the failure of the static compressive strength can often be detected and predicted.

Fatigue limit failure is gradually improved, but it is difficult to predict in advance, so its damage is higher.

Magnesium AZ31 Machined part

3. Tribology Failure

Tribological failure mainly includes erosion, wear, deviation, gluing and contact fatigue. Etching is a kind of photo catalytic or organic chemical corrosion condition on the surface of metal materials. Its conclusion will lead to rust on the surface of parts and reduce the fatigue relieving ability of parts. Wear is the loss or conversion of chemical substances on the surface of two touching surfaces in the process of uniform movement.

Gluing is caused by the destruction of the oil slick between two relative speed surfaces. Under the fast and light load working conditions, parts of the two surfaces stick together. When the position where the two surfaces adhere to each other is torn off and grooves are generated on the surface along the relative speed direction, it is called gluing.

Touch fatigue refers to the condition that cracks or particles fall off on the surface subjected to the long-term effect of touch stress.

Some parts can work normally only under certain operating conditions. For example, the rolling bearing with liquid friction can work normally when the oil film is too thin, otherwise the rolling bearing will have failures in the form of overheating, gluing, wear, etc., which belongs to the tribological failure.

For another example, the deflection of the pulley and the wear of the shaft of the screw tooth are examples of tribological failure.

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