Fatigue tests and assessment of high-yield-strength cold-rolled large-diameter ribbed steel bars

Cold-rolled large-diameter ribbed steel bars have higher strength than hot-rolled steel bars but are susceptible to cracks, particularly at the root of the ribs, owing to the manufacturing process. This study investigated steel bars of 75 mm diameter produced using different manufacturing processes. Extensive testing of the specimens was conducted, including high-cycle fatigue tests under various high loadings, fatigue crack growth (FCG) rate at a stress ratio of 0.85, fracture surface analysis, and statistical analysis of the probabilities and FCG mechanisms. A fatigue life model considering the initial cracks in a ribbed steel bar was proposed based on the Paris and Walker models. Fewer rolling cycles and higher tempering temperatures accelerated the growth rate of the initial cracks. Finally, the FCG life was calculated using the integral equation under diverse processes and loading conditions. The critical thresholds for the initial crack length demonstrated the ability to withstand 2 × 10 6 cycles under a stress amplitude of 88 MPa without fracture.