Practical determination method of the threshold stress intensity factor range Δk_th

It is necessary to identify relationship between the fatigue crack propagation rate and the stress intensity factor range, if the fracture mechanics approach is applied to evaluate the fatigue crack growth evolution. In addition, identification of the stress intensity factor range of fatigue crack growth threshold (ΔK_th) is important to evaluate the structural integrity from the view of fatigue performance. ASTM standard E647 "Standard Test Method for Measurement of Fatigue Crack Growth Rates" is widely known as a de fact standard to determine the value of ΔK_th. However, a considerably long time is required to perform the determination of ΔK_th value. Therefore, it is expected to cut the experimental period for ΔK_th determination. Efficient and time saving procedure for determining ΔK_th value comparing with ASTM-E647 is proposed in this study. Many fatigue crack propagation test data were applied to verify the validity of our proposed method. It is expected to be able to complete the experiment for determining ΔK_th value at a stage where the fatigue crack propagation rate is one order larger comparing with ASTM-E647.