What are the factors affecting the fatigue strength of the finger spring?

What are the factors affecting the fatigue strength of the finger spring?

1. There is a certain relationship between the yield strength and the fatigue limit of yield strength materials. Generally speaking, the higher the yield strength of the material, the higher the fatigue strength. Therefore, in order to improve the fatigue strength of the spring, please try to increase the yield strength of the spring material. Material with a high ratio of strength or yield strength to tensile strength. For the same material, fine grain structure has higher yield strength than coarse grain structure.

2. The maximum stress of the surface state mainly occurs on the surface of the spring material, so the surface quality of the spring has a great influence on the fatigue strength. Cracks, defects and scratches in the rolling, stretching and rolling process of spring materials are usually the causes of spring fatigue fracture. The smaller the surface roughness is, the smaller the stress concentration is and the higher the fatigue strength is. Influence of material surface roughness on fatigue limit. With the increase of surface roughness, the fatigue limit decreases. Under the condition of the same roughness, different steel types and rolling methods have different reduction degrees of fatigue limit, for example, the reduction of cold coil spring is less than that of hot coil spring. Due to the heating of steel coil spring and its heat treatment, the surface of the spring material will become rough and decarbonized due to oxidation, thus reducing the fatigue strength of the spring. Grinding, pressing, sandblasting and rolling material surfaces. Both can increase the fatigue strength of the spring.

3. Size effect The larger the size of the material, the greater the possibility of defects due to various cold working and hot working processes, and the greater the possibility of surface defects, which will lead to decreased fatigue performance. Therefore, the influence of size effect should be considered when calculating the fatigue strength of spring.

4. Metallurgical defects Metallurgical defects refer to non-metallic inclusions, bubbles, segregation of elements in materials, etc. The presence of inclusions on the surface is a source of stress concentration, which may cause fatigue cracks to occur prematurely between the interface between the inclusions and the substrate. Vacuum smelting, vacuum casting and other measures can greatly improve steel quality.