A Novel Approach for ∆K Estimation in the Fatigue Threshold Region Based on ΔKth and Kmax,th

Abstract

A novel procedure, proposed by Kujawski and Vasudevan 1, has been evaluated as an alternative to the ASTM E647 stand ard for determining the ∆Kth and Kmax,th thresholds. This method relies solely on the actual propagation of cracks, which oc curs only when both thresholds are satisfied simultaneously. For long cracks, a more efficient estimation of thresholds can be achieved. Compared to the ASTM E647 standard (R=0.1, ∆Kth=2.95MPa√m), the new methodology for the same R yielded a value of ∆Kth=2.50MPa√m and determined a maximum stress threshold of Kmax,th=3.35MPa√m. A correlated parameter, K*=Kmaxα·∆K1-α, α=0.5 for Al 2024 T3 alloy, was employed to provide an effective relation between the loading ratio and the threshold conditions, with K* values ranging from 2.8 to 3MPa√m for R-ratios from 0.1 to 0.7. The implementation of this tech nique has the potential to reduce testing time and postprocessing efforts by minimizing the need for crack propagation calcu lations. This method provides valuable insights into the material behavior near the fatigue threshold for the specific cases and material investigated.