Causes of fatigue and fracture of floor springs
The surface state stress 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, flaws and scars caused by spring materials during rolling, drawing and coiling are often the causes of spring fatigue and fracture.
The smaller the surface roughness of the material, the smaller the stress concentration and the higher the fatigue strength. The effect of material surface roughness on fatigue. As the surface roughness increases, fatigue decreases. In the case of the same roughness, different steel grades and different coiling methods have different degrees of fatigue reduction. For example, the degree of reduction of cold-coiled springs is smaller than that of hot-coiled springs. Because the steel hot coil spring and its heat treatment are heated, the surface of the spring material becomes rough due to oxidation and decarburization occurs, which reduces the fatigue strength of the spring. Grinding, pressing, shot blasting and rolling on the surface of the material. Both can improve the fatigue strength of the spring.