Intergrated Evaluation Method for Fatigue Limit of Notched Steel with ΔK_(th) Value

摘要

It is the big problem to evaluate the fatigue limit σ_w in order to safely design structures and machines. Under the condition of the fatigue crack initiation limit σ_(w1), the present author defined the initial crack size area~(1/2) using the characteristic elastic field of the notch, the half length of the fatigue crack a and a notch depth t. Using this area~(1/2), the methods of calculating ΔK_(th) and σ_(w1) were proposed. In addition to it, in this condition it is made sure that ΔK_(th) exists on the band from ΔK_(th) prediction line of the micro fatigue crack within 18% error. Using ΔK_(th) calculated by the prediction line and the value of area~(1/2), this evaluating method of σ_(w1) was confirmed with annealed 0.35% carbon steel. As a result, it was confirmed that this method to evaluate σ_(w1) is within 18% error. Moreover it was also confirmed that the σ_(w1) value by this prediction method is within 10% error when the predicted σ_(w1) value is greater than σ_(w2).