There are many failure modes of parts, which can be classified into three types, excessive deformation, fracture and surface damage failure. Each type can be divided into several different situations.
Here is mainly to share with you the form of excessive deformation failure. The so-called excessive deformation, that is, to some extent, the deformation of the original design function of the part is weakened.
1. Excessive elastic deformation failure
The part fails due to excessive elastic deformation, which is called elastic deformation failure. For example, for a shaft-shaped part that is bent and twisted, the excessive deformation amount may cause severe eccentric load or even meshing of the meshing parts on the shaft, thereby causing the transmission to fail.
2. Excessive plastic deformation failure
Plastic deformation occurs when the stress experienced by the part exceeds the yield limit of the material. Excessive plastic deformation changes the relative position between the parts, making the entire machine malfunction. For example, the tooth shape of the gear in the gearbox is plastic deformed to cause poor meshing, vibration and noise, and even pinching and breaking teeth. If the key is twisted, the bolt is stretched after being load., it will cause excessive plastic deformation failure as well.
3. Creep deformation failure
Parts subjected to long-term fixed loads may undergo creep during operation (especially at high temperatures) (ie, the amount of deformation increases with time as stress is constant). When the part creep variable has passed the specified range, it is in an unsafe state. In severe cases, it may collide with other parts, making the device unable to work normally. Components such as boilers, steam turbines, gas turbines, aerospace engines, and other heat engines often fail due to plastic deformation and stress relaxation caused by creep.
