Suzhou Zhaoneng Precision Spring Hardware Co., Ltd.
Address£ºNo. 161, Shilin Road, Suzhou High-tech Zone
Several Factors Affecting Fatigue Strength of Springs
1. In general, the higher the yield strength of the material, the higher the fatigue strength. Therefore, in order to improve the fatigue strength of the spring, the yield strength of the spring material should be improved, and the yield strength of the material should be improved. Or a material having a high ratio of yield strength to tensile strength. For the same material, the fine grain structure has a higher yield strength than the fine grain structure.
2. The surface state of the maximum stress occurred in the spring material surface, so the surface quality of the spring on the fatigue strength of a great impact. Spring material in the rolling, drawing and rolling process caused by cracks, defects and scars and other defects are often caused by spring fatigue fracture reasons.
The smaller the surface roughness, the smaller the stress concentration and the higher the fatigue strength. Effect of Material Surface Roughness on Fatigue Limit. As the surface roughness increases, the fatigue limit decreases. In the case of the same roughness, the fatigue limit of different steel grades and different rolling methods is also different, for example, the degree of reduction of cold coil spring is smaller than that of hot coil spring. Because the steel coil spring and its heat treatment heat, due to oxidation of the surface roughness of the spring material and produce decarburization phenomenon, thus reducing the fatigue strength of the spring.
The surface of the material grinding, strong pressure, shot blasting and rolling and so on. Can increase the fatigue strength of the spring.
3. The greater the size of the size effect material, the higher the possibility of defects due to the various cold and hot working processes, and the greater the possibility of surface defects, all of which result in deterioration of the fatigue properties. Therefore, when calculating the fatigue strength of the spring to consider the size effect.
4. Metallurgical defects Metallurgical defects are nonmetallic inclusions, bubbles, segregation of elements in the material, and so on. The existence of the inclusions on the surface is a stress concentration source, leading to premature fatigue cracks between the inclusions and the matrix interface. Vacuum smelting, vacuum casting and other measures, can greatly improve the quality of steel.
5. Corrosive media spring in the corrosive media, due to surface pitting or surface grain boundary corrosion has become a source of fatigue, under the action of the stress will gradually expand and lead to fracture. For example, working in the spring of spring steel, fatigue limit of only 10% to 25% in the air. The effect of corrosion on the fatigue strength of the spring is not only related to the number of times the spring is subjected to variable loads, but also to the working life. Therefore, the design life of the spring should be taken into account when calculating the corrosion affected by the spring.
Corrosion conditions in the work of the spring, in order to ensure its fatigue strength, corrosion resistance can be used high-material, such as stainless steel, non-ferrous metals, or surface protective layer, such as coating, oxidation, spray, paint and so on. Practice shows that cadmium can greatly improve the fatigue limit of the spring.
6. Temperature The fatigue strength of carbon steel decreases from room temperature to 120 ¡ã C and rises from 120 ¡ã C to 350 ¡ã C. The temperature is higher than 350 ¡ã C and decreases again. There is no fatigue limit at high temperature. In the high-temperature conditions of work under the spring, to consider the use of heat-resistant steel. At lower temperatures, the fatigue limit of the steel is increased.