Springs are used in many different mechanical and electronic devices. The reliability of the springs directly affects the stability and service life of these devices. Based on our decades of experience, EASON Spring summarizes the six main factors that affect the fatigue life of springs.
- Yield Strength
There is a certain relationship between the yield strength of the material and its fatigue limit. Generally, the higher the yield strength of the material, the higher the fatigue strength. Therefore, to improve the fatigue strength of a spring, we need to increase the yield strength of the spring material or use materials with a high ratio of yield strength to tensile strength. For the same material, the fine-grained structure has a higher yield strength than the coarse-grained structure.
- Surface Condition
The surface condition of a spring has a great influence on its fatigue strength. Defects such as cracks, defects, and scars caused during the rolling, drawing, and coiling processes are often the causes of fatigue fractures of springs. The smoother the surface of the material, the smaller the stress concentration and the higher the fatigue strength.
- Size Effect
The larger the size of the material, the more likely it is to have defects caused by various cold and hot working processes, and the greater the possibility of surface defects. All these factors will lead to a decrease in fatigue performance. Therefore, when calculating the fatigue strength of springs, we must consider the size effect.
- Metallurgical Defects
Metallurgical defects refer to non-metallic inclusions, bubbles, element segregation, etc. in the material. Inclusions on the surface are stress concentration points and can cause premature fatigue cracking between the inclusion and the matrix. Using vacuum melting and vacuum casting can greatly improve the quality of steel.
- Corrosive Media
When springs work in corrosive media, the surface will be pitted or corroded, generating fatigue sources under varying stresses, which will eventually lead to fractures. For example, the fatigue limit of spring steel in fresh water is only 10% to 25% of that in the air. The influence of corrosion on the fatigue strength of springs is not only related to the number of load cycles but also to the service life. Therefore, when designing springs that are affected by corrosion, we must consider the service life. To ensure the fatigue strength in corrosive environments, materials with high corrosion resistance, such as stainless steel or non-ferrous metals, can be used, or protective coatings such as electroplating, oxidation, spraying, or painting can be applied.
- Temperature
The fatigue strength of carbon steel decreases from room temperature to 120°C, increases from 120°C to 350°C, and then decreases again above 350°C. For springs used at high temperatures, heat-resistant steel should be considered. At temperatures below room temperature, the fatigue limit of steel increases.
For more than forty years, EASON SPRING has been committed to providing higher-quality and more durable springs. We welcome customers to consult and customize high-quality springs.
