Types of mechanical parts failure forms and influencing factors Do you know?

Failure of mechanical parts means that parts are partially or completely lost in design during use. The part is completely destroyed and cannot continue to work; or the part has been seriously damaged, and if it continues to work, it will lose its safety; or if it can work safely, the loss of design accuracy will be invalid. In order to prevent the failure of parts, it is necessary to carry out failure analysis on the parts, that is, by judging the failure form of the parts, determining the failure mechanism and causes of the parts, selecting materials, determining a reasonable processing route, and proposing measures to prevent failure.

 

 

1. Mechanical parts failure form

 

The common failure modes of mechanical parts can be divided into three types: excessive deformation failure, fracture failure and surface damage failure.

 

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(1) Excessive deformation failure: failure of the part due to excessive deformation exceeding the allowable range. It mainly includes failure modes such as excessive elastic deformation, plastic deformation and creep occurring at high temperatures.

 

(2) Fracture failure: a phenomenon of separation into two or more parts that are not connected due to excessive bearing load or fatigue damage. Fracture is the most serious form of failure, including ductile fracture failure, low temperature brittle fracture failure, fatigue fracture failure, creep fracture failure and environmental failure failure.

 

 

(3) Surface damage failure: failure caused by damage or dimensional change of the surface of the part due to the relative friction of the surface or the corrosion of the environmental medium. It mainly includes forms such as surface wear failure, corrosion failure, and surface fatigue failure.

 

It should be pointed out that the same mechanical parts often work not only as a failure mode. However, there is always a way for the parts to fail. The core problem of failure analysis is to find out the main failure modes.

 

 

2. Reasons for failure of mechanical parts

 

There are many factors that cause the failure of mechanical parts, which are complicated and involve many aspects such as structural design of parts, material selection, processing and manufacturing of materials, assembly and maintenance of products.

 

(1) Unreasonable design: Mainly refers to the incorrect or unreasonable structure and shape of parts, such as gaps in parts, small arc angles, transition zones of different shapes, etc. On the other hand, it means that the working conditions and overload conditions of the parts are insufficiently estimated, resulting in insufficient actual working ability of the parts, resulting in early failure of the parts.

 

(2) Unreasonable material selection: In the design, the form of part failure is judged incorrectly, and the selected material performance cannot meet the working conditions; the performance index based on the material cannot reflect the resistance of the material to the actual failure form, and the wrong material is selected; The material used is of poor quality, the composition or performance is unqualified, and the design requirements are not met.

 

(3) Unreasonable processing technology: improper processing of parts may cause various defects, resulting in parts failing earlier in use. Such as overheating, over-burning and banded structure during hot working; decarburization, deformation and cracking occur during heat treatment; deeper knife marks, grinding cracks, etc. occur during cold working.

 

(4) Improper installation and installation: the assembly and installation process does not meet the technical requirements. If the installation is too tight, too loose, the alignment is not allowed, and the fixing is unstable, the parts may not work properly or fail prematurely; in addition, Violation of the rules during operation, overloading, overspeed, failure to repair and maintain on time will also cause premature failure of parts.