The touch spring tells you several factors that affect the fatigue strength of the spring

The touch spring tells you several factors that affect the fatigue strength of the spring

1, there is a certain relationship between the yield strength of the material and the fatigue limit, 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 should try to improve the yield strength of the spring material, or the yield strength and tensile strength ratio of high materials. For the same material, the fine grain structure has higher yield strength than the coarse grain structure.

2, the maximum stress of the surface state occurs in the surface of the spring material, so the surface quality of the spring has a great impact on the fatigue strength. Cracks, defects and scars caused by spring materials in the rolling, drawing and winding process are often 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 kinds of steel and different winding methods have different reduction degrees of fatigue limit. For example, the reduction degree of cold coil spring is smaller than that of hot coil spring. Because the steel hot coil spring and its heat treatment heating, due to the oxidation of the spring material surface rough and decarbonization phenomenon, so as to reduce the fatigue strength of the spring.

The material surface is grinding, pressing, shot blasting and rolling, etc. Can improve the fatigue strength of the spring.

3. Size effect The larger the size of the material, the higher the possibility of defects caused by various cold working and hot working processes, and the greater the possibility of surface defects. These reasons will lead to the decline of 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, and so on. The inclusion on the surface is the source of stress concentration, which leads to premature fatigue cracks between the inclusion and the matrix interface. Vacuum smelting, vacuum casting and other measures can greatly improve the quality of steel.

5, the corrosive medium spring in the corrosive medium work, due to the surface pitting or surface grain boundary corrosion and become a fatigue source, under the action of variable stress will gradually expand and lead to fracture. For example, the fatigue limit of spring steel working in fresh water is only 10%~25% of that in air. The influence of corrosion on the fatigue strength of spring is not only related to the number of times the spring is subjected to variable load, but also to the working life of the spring. Therefore, the working life should be taken into account when designing and calculating the spring affected by corrosion.

Spring working under corrosive conditions, in order to ensure its fatigue strength, can be used with high corrosion resistance of materials, such as stainless steel, non-iron metal, or the surface of the protective layer, such as coating, oxidation, spray, paint, etc. The practice shows that cadmium plating can greatly improve the fatigue limit of spring.

6, temperature carbon steel fatigue strength, from room temperature to 120℃ decreases, from 120℃ to 350℃ and rise, the temperature is higher than 350℃ and then decreased, there is no fatigue limit at high temperature. For springs working under high temperature conditions, heat-resistant steel should be considered. The fatigue limit of steel increases at below room temperature.