Mechanical loss of working ability is called failure,machine parts loss of specified working ability is called failure.The failure of machinery is inseparable from the failure of parts.Due to the normal wear and tear of parts or physical and chemical changes caused by parts deformation,fracture,erosion and other parts caused by the failure of the fault,this fault is also called natural fault.

1.Wear and tear of parts

Wear is the most important and common form of parts failure.

2.Deformation of parts

Machine in the process of work,due to the effect of the force,so that the size and shape of the parts of the phenomenon is called deformation.The deformation of metal includes elastic deformation and plastic deformation.

3.Fracture of parts

Parts in the external force under the action of the load,the first occurrence of elastic deformation,when the stress caused by the load beyond the elastic limit and continue to increase,the material may produce plastic deformation,the final stress exceeds the strength limit fracture.

4,pitting

The point spalling of parts under cyclic contact stress is called fatigue pitting.Parts by the chemical and electrochemical action of the surrounding medium so that the surface metal damage is called corrosion;Parts under the action of temperature changes and medium surface needle-like holes,and constantly expand known as cavitation erosion.Fatigue pitting,corrosion and cavitation are collectively referred to as erosion loss.