Current Journal of Applied Science and Technology

This study compares the Stromeyer, Basquin, and Wöhler fatigue models for E235 steel under three surface conditions: untreated, shot-peened, and shot-peened followed by electroless nickel coating. Fatigue specimens were extracted from a pump-rotor section selected to represent a region susceptible to service-related cracking. Tests were conducted in air at room temperature under force control, with a mechanical stress ratio of 0.1, a frequency of approximately 60 Hz, and a stopping criterion of 2 × 10^6 cycles or a 2 Hz reduction in test frequency. The experimental results were analysed using the ESOPE software to estimate model parameters, fatigue limits, standard deviations, and rejection rates. For the untreated condition, the Stromeyer model produced a converted fatigue-limit estimate of 344.6 MPa and a rejection rate of 75.82%. Shot peening increased the corresponding estimate to 419.8 MPa and reduced the rejection rate to 31.57%. Following electroless nickel coating, the estimated value decreased to 299.6 MPa, while the rejection rate increased to 86.69%. Among the examined conditions, the shot-peened specimens therefore showed the highest estimated fatigue resistance and the lowest rejection rate. The results indicate that model performance varies substantially with surface condition and experimental scatter. Under the tested conditions, the Stromeyer model provided the most consistent representation of the shot-peened dataset, whereas the untreated and nickel-coated datasets showed greater variability and lower fitting reliability.