FATIGUE-CRACK GROWTH OF TI-62222 TITANIUM-ALLOY UNDER CONSTANT AMPLITUDE AND MINITWIST FLIGHT SPECTRA AT 25-DEGREES-C AND 175-DEGREES-C

Fatigue crack growth behavior was investigated for Ti-62222 titanium a lloy under constant amplitude (R=0.1 and 0.5) and miniTWIST flight spe ctra at 25 and 175 degrees C. Crack closure was observed at threshold and near threshold for both temperatures with R = 0.1 but not for R = 0.5. Based upon applied or effective Delta K, fatigue crack growth beh avior for a given R ratio showed no significant temperature effect. Mi niTWIST flight spectra fatigue crack growth life at 175 degrees C, how ever, was 2.5-3.5 times greater than at 25 degrees C. Fatigue crack gr owth life calculations using NASA/FLAGRO were conservative. Fatigue cr ack growth was transgranular with SEM fracture surface morphology depe ndent upon both Delta K and temperature with significant increase in s econdary cracking at 175 degrees C. (C) 1997 Elsevier Science Ltd. All rights reserved.