fatigue Many mechanical parts and engineering components work under alternating loads. Under the action of alternating load, although the stress level is lower than the yield limit of the material, after a long period of repeated stress cycle, sudden brittle fracture occurs. This mechanical part is called fatigue of metal material. The characteristics of fatigue fracture of metal materials are: (1) The load stress is alternating; (2) The effect of the load is longer; (3) The fracture occurs instantaneously; (4) Whether it is a plastic material or a brittle material, it is brittle in the fatigue fracture zone. Therefore, fatigue fracture is the most common and dangerous form of fracture in engineering. The fatigue phenomenon of metal materials can be divided into the following types according to different conditions: (1) High cycle fatigue: refers to the fatigue of the number of stress cycles of more than 100000 under the condition of low stress (the working stress is lower than the yield limit of the material, even lower than the elastic limit). It is the most common type of fatigue damage. High cycle fatigue is generally referred to as fatigue. (2) Low cycle fatigue: refers to the fatigue of the stress cycle number below 10000~100000 under high stress (working stress close to the yield limit of the material) or high strain condition. Since the alternating plastic strain plays a major role in such fatigue failure, it is also called plastic fatigue or strain fatigue. (3) Thermal fatigue: refers to the fatigue damage caused by the repeated action of thermal stress caused by temperature changes. (4) Corrosion fatigue: refers to the fatigue damage of machine parts caused by the combined action of alternating load and corrosive medium (such as acid, alkali, seawater, reactive gas, etc.). (5) Contact fatigue: This refers to the contact surface of the machine parts. Under the repeated action of contact stress, pitting or surface crushing and peeling occur, which causes failure of the machine parts. Plasticity Plasticity refers to the ability of a metal material to produce permanent deformation (plastic deformation) under the action of external forces of the load without being broken by plastic deformation. When the metal material is stretched, the length and the cross-sectional area are changed. Therefore, the plasticity of the metal can be measured by the elongation of the length (elongation) and the shrinkage of the section (sectional shrinkage). The greater the elongation and the reduction of the section of the metal material, the better the plasticity of the material, that is, the material can withstand large plastic deformation without damage. Generally, a metal material having an elongation of more than 5 percent is called a plastic material (such as low carbon steel), and a metal material having an elongation of less than 5 percent is called a brittle material (such as gray cast iron). The plastic material has good plastic deformation in a large macroscopic range, and the metal material is strengthened by plastic deformation while plastic deformation, thereby improving the strength of the material and ensuring the safe use of the parts. In addition, plastically good materials can be smoothly processed in certain molding processes, such as stamping, cold bending, cold drawing, and straightening. Therefore, when selecting metal materials as mechanical parts, certain plasticity indexes must be met. Self Adhesive Standard Floor Protection Moving Floor Protection,Floor Protection Paint,Self Adhesive Floor Protection,Outdoor Floor Protection Suzhou Surface Protective New Material Technology Co.,Ltd , https://www.surfaceprotective.com