used for the first time in springs fabrication process, several new steels have been developed attempting to increase the spring strength aiming vehicle mass reduction as well as increase in the fatigue life. Therefore, the shot peening process has needed shot with higher hardness, leading to both shot and equipment life reduction. Warm shot peening at or under the tempering temperature may be a solution to reduce or even avoid these effects. However, the effect of warm shot peening in improving fatigue strength has not been well established and not extensively studied. Recently, Totten et all (2002) and Tange et all (1999) studied the effect of warm shot peening of suspension coil spring. In this work, in order to get a better association of the strain hardening and residual stress as a function of shot peening temperature and its effect on fatigue strength of leaf springs, specimens of SAE5160 were penned at 25ºC, 100ºC, 150ºC, 200ºC, 250ºC and 300ºC and fatigue tested in three point bending. 2 EXPERIMENTAL
2.1 Material and test specimens The material used in this work was a SAE 5160 steel plate with 750 mm length, 63.5 mm wide and 11.4 mm thick. The geometry is quite similar to one type of leaf spring produced for vehicles. The material’s chemical composition is presented in Table (1).Table 1. Chemical composition of the SAE 5160 steel. Chemical Element C Mn Si P S Cr % wt 0.59 0.96 0.22 0.016 0.018 0.86 2.2 Fatigue test The fatigue specimens were divided in five groups, with four specimens each. The groups were placed in the furnace, heated at each previous established temperature, and remained in this temperature for 15 minutes. Once the specimens reached the required temperature they were one by one transferred to the shot peening machine. As presented in Table (2), the groups were formed by specimens selected by its hardness after quenching and tempering heat treatments, as well as by the shot temperature. The fatigue tests were carried in three point bending loading condition, 2 Hz frequency and load rate equal to zero. The test ended when the specimen was broken and the number of cycles was registered. The main idea was to compare the fatigue life of the leaf spring, with the surface treated in one of the conditions presented in Table (2). Therefore, just for comparison, there was no need to get the S-N curve and all the fatigue tests were performed at a constant maximum flexural stress of 610 MPa, that was previously established by the spring maker and it was based on the maximum stresses that the component may be submitted in life.
You've reached the end of your free preview.
Want to read all 6 pages?
- Spring '18
- Dr. maarten bakker