Factors Influencing Low-Cycle Crack Growth in 2014-T6 Aluminum Sheet at -320 F (77 K)

An investigation was conducted to determine the low-cycle under 10 000 cycles crack growth characteristics of through- center- cracked specimens 0.060 in. 0.152 cm thick subjected to tension-tension cyclic loading. The following factors were studied 1 minimum to maximum initial stress intensity ratio R sub i 2 the maximum gross stress applied, as percentage of critical fracture stress and 3 cyclic rate. The crack growth rate was found to be a function of stress level expressed as percentage of critical fracture stress for specimens tested at the same R. value. A crack growth relation was developed which takes into account changes in R. in the low-cycle region. When the cycle rate was decreased from 0. 5 to 0.05 Ha, the cyclic life was reduced, but only for high initial stress intensities.