Material Prestraining Effect on Fatigue Performance of Q235 and Q355 Structural Steels

The primary difference in fatigue performance between cold-formed steel and hot-rolled steel stems from cold work strengthening. Therefore, this study focuses on the influence of prestraining on the high-cycle fatigue performance of Q235 and Q355 steels. High-cycle fatigue tests were conducted on specimens subjected to different levels of prestraining (0%, 1%, 5%, 10% or 12%, and 16% or 20%). Subsequently, S-N (stress versus number of cycles) curves and fatigue limits were obtained, along with calculated fatigue ratio values. The results reveal that with the increase in prestraining, fatigue life is raised within approximately 500,000 cycles. Additionally, the slope of the S-N curve is enhanced but remains consistently below the specified value. Overall, the fatigue limit exhibits an initial increase followed by a decrease. Moreover, the fatigue ratio demonstrates a monotonous decrease. Further tests have confirmed that specimens extracted from steel pipes still present similar patterns. Through theoretical analysis, it has been discovered that the fatigue limit of prestrained steel can be expressed as the product of the nominal yield strength and a quadratic function of the variation coefficient in nominal yield strength. Compared with existing findings, it is found that the above patterns are applicable to ferrite-pearlite steel.