What factors affect the fatigue strength of springs?
UP data:2015-06-27
What factors affect the fatigue strength of springs?
There is a certain relationship between yield strength and fatigue limit of 1. yield strength materials. In general, the higher the yield strength and the higher the fatigue strength, the yield strength of the spring material should be improved to improve the fatigue strength of the spring, or the material with high ratio of yield strength to tensile strength should be adopted. For the same material, fine grain structure has higher yield strength than coarse and fine grain structure.
2. the maximum stress in the surface state mostly occurs on the surface of the spring material, so the surface quality of the spring has a great influence on the fatigue strength. Defects such as cracks, defects and scars caused by spring materials during rolling, drawing and rolling are often the causes of fatigue fracture of springs.
The smaller the surface roughness, the smaller the stress concentration and the higher the fatigue strength. The effect of the surface roughness of the material on the fatigue limit. With the increase of surface roughness, the fatigue limit decreases. In the case of the same roughness, the degree of the fatigue limit of different steel and different rolling methods is different, for example, the reduction of cold coil springs is smaller than that of hot coil springs. Because the steel hot coil spring and its heat treatment are heated, the surface of the spring material is rough and the phenomenon of decarbonization is produced by oxidation, which reduces the fatigue strength of the spring.
Grinding, pressing, shot blasting and rolling of material surface. The fatigue strength of the spring can be improved.
The greater the size of the 3. size effect material is, the higher the possibility of defects caused by cold and hot processing, the greater the possibility of producing surface defects, which will lead to a decline in fatigue properties. Therefore, the effect of size effect should be taken into account when calculating the fatigue strength of springs.
4. metallurgical defects metallurgical defects refer to non-metallic inclusions, bubbles and segregation of elements in materials. The inclusion on the surface is a stress concentration source, which causes premature fatigue cracks between the interface between the inclusions and the matrix. The quality of steel can be greatly improved by vacuum smelting and vacuum pouring.
When 5. corrosion medium works in corrosive medium, it becomes a fatigue source due to surface pitting or surface grain boundary being corroded, which will gradually expand under stress variable and cause fracture. For example, spring steel working in fresh water has a fatigue limit of only 10%~25% in air. The effect of corrosion on the fatigue strength of springs is not only related to the number of times the spring is subjected to variable loads, but also to the working life. Therefore, when designing and calculating the spring affected by corrosion, the service life should be taken into account.
In order to ensure the fatigue strength of the spring working under corrosion conditions, the material with high corrosion resistance, such as stainless steel, non iron metal, or surface plus protective layer, such as coating, oxidation, spray, paint and so on. Practice shows that cadmium plating can greatly improve the fatigue limit of springs.
The fatigue strength of 6. temperature carbon steel decreased from room temperature to 120 C, increased from 120 to 350 C, and then decreased after the temperature is higher than 350, and there was no fatigue limit at high temperature. When working under high temperature conditions, the use of heat-resistant steel should be considered. Under room temperature condition, the fatigue limit of steel increases.
What factors affect the fatigue strength of springs?
There is a certain relationship between yield strength and fatigue limit of 1. yield strength materials. In general, the higher the yield strength and the higher the fatigue strength, the yield strength of the spring material should be improved to improve the fatigue strength of the spring, or the material with high ratio of yield strength to tensile strength should be adopted. For the same material, fine grain structure has higher yield strength than coarse and fine grain structure.
2. the maximum stress in the surface state mostly occurs on the surface of the spring material, so the surface quality of the spring has a great influence on the fatigue strength. Defects such as cracks, defects and scars caused by spring materials during rolling, drawing and rolling are often the causes of fatigue fracture of springs.
The smaller the surface roughness, the smaller the stress concentration and the higher the fatigue strength. The effect of the surface roughness of the material on the fatigue limit. With the increase of surface roughness, the fatigue limit decreases. In the case of the same roughness, the degree of the fatigue limit of different steel and different rolling methods is different, for example, the reduction of cold coil springs is smaller than that of hot coil springs. Because the steel hot coil spring and its heat treatment are heated, the surface of the spring material is rough and the phenomenon of decarbonization is produced by oxidation, which reduces the fatigue strength of the spring.
Grinding, pressing, shot blasting and rolling of material surface. The fatigue strength of the spring can be improved.
The greater the size of the 3. size effect material is, the higher the possibility of defects caused by cold and hot processing, the greater the possibility of producing surface defects, which will lead to a decline in fatigue properties. Therefore, the effect of size effect should be taken into account when calculating the fatigue strength of springs.
4. metallurgical defects metallurgical defects refer to non-metallic inclusions, bubbles and segregation of elements in materials. The inclusion on the surface is a stress concentration source, which causes premature fatigue cracks between the interface between the inclusions and the matrix. The quality of steel can be greatly improved by vacuum smelting and vacuum pouring.
When 5. corrosion medium works in corrosive medium, it becomes a fatigue source due to surface pitting or surface grain boundary being corroded, which will gradually expand under stress variable and cause fracture. For example, spring steel working in fresh water has a fatigue limit of only 10%~25% in air. The effect of corrosion on the fatigue strength of springs is not only related to the number of times the spring is subjected to variable loads, but also to the working life. Therefore, when designing and calculating the spring affected by corrosion, the service life should be taken into account.
In order to ensure the fatigue strength of the spring working under corrosion conditions, the material with high corrosion resistance, such as stainless steel, non iron metal, or surface plus protective layer, such as coating, oxidation, spray, paint and so on. Practice shows that cadmium plating can greatly improve the fatigue limit of springs.
The fatigue strength of 6. temperature carbon steel decreased from room temperature to 120 C, increased from 120 to 350 C, and then decreased after the temperature is higher than 350, and there was no fatigue limit at high temperature. When working under high temperature conditions, the use of heat-resistant steel should be considered. Under room temperature condition, the fatigue limit of steel increases.
