Investigation of fracture design for medium carbon steel under extra-low cyclic fatigue in axial loading

The extra-low cyclic fracture problem of medium carbon steel under axial fatigue loading was investigated. Several problems, such as the relations of the cycle times to the depth and tip radius of the notch, loading frequency, loading range and the parameters of fracture design for medium carbon steel on condition of extra-low axial fatigue loading were discussed based on the experiments. Experimental results indicated that the tension-pressure fatigue loading mode was suitable for extra-low cyclic fatigue fracture design of medium carbon steel and it resulted in low energy consumption, fracture surface with high quality, low cycle times, and high efficiency. The appropriate parameters were as follows: loading frequency 3–5 Hz, notch tip radius r = (0.2–0.3) mm, opening angle α = 60°, and notch depth t = (0.14–0.17)D.