CYCLIC STRESS-STRAIN BEHAVIOR AND LOW-CYCLE FATIGUE OF TI-6-4 AT 260-DEGREES-C

Low-cycle fatigue tests on Ti 6-4 (Ti-6Al-4V) have been carried out at 260-degrees-C under strain-controlled conditions with constant strain amplitude and increasing multistep strain levels. The results of constant strain amplitude tests were used to establish the fatigue diagram whereas the multistep tests were examined to assess the cyclic stress-strain behavior in comparison with the conventional stress-strain curve. Most of the tests were carried out under zero-to-tension conditions in the intermediate-cycle range (N(f) congruent-to 3 x 10(3) to 10(5) cycles). The effect of prior strain cycling on the tensile properties was also investigated. The experimental data is discussed together with theoretical evaluations. In addition, microstructural examinations of the rupture surfaces have been made to show evidence on the type of crack initiation sites and on the crack propagation modes at different strain levels.