A Rapid Method for Generation of a Haigh Diagram for High Cycle Fatigue

A rapid test method is described for generating data points for a Haigh diagram for Ti-6A1-4V at a constant life of 10⁷ cycles at room temperature. It involves subjecting specimens to loading blocks of 10⁷ fatigue cycles and progressively increasing the load until failure occurs. An equivalent stress is obtained for each test specimen for plotting on the Haigh diagram. The method is applied to tests conducted at stress ratios (ratio of minimum to maximum stress) from R=-l to R=0.9. The validity of the method is confirmed by comparing data with those obtained using the conventional S-N interpolation approach at values of R=0.1, 0.5, and 0.8. The rapid testing technique is then extended to the generation of a Haigh diagram for the same material subjected to prior low cycle fatigue (LCF) for ten percent of its LCF life. No degradation of the fatigue limit is observed from subsequent HCF testing using the rapid testing technique.