Temperature effect on crack propagation properties of aluminum alloys in aircraft

Fatigue properties on crack propagation rate at low and elevated temperatures are the precondition of damage tolerance design for aviation metallic structures. Therefore, in order to determine fatigue properties on crack propagation rate, fatigue tests were performed on six categories of aluminum alloys (i. e. 2024-T351, 2397-T8, 6061-T651, 7050-T7451, 7050-T7452, 7475-T761) at five kinds of temperatures (-70℃, -54℃, 25℃, 125℃, 150℃) under constant amplitude loading, and fatigue crack propagation properties were determined and the comparisons between fatigue properties on crack propagation rate at different temperatures were carried out. The mechanisms of temperature effect on crack propagation rate were deduced from fractographic studies by using scanning election microscope (SEM). The results show that, compared with the situation at 25℃, logarithmic crack propagation resistance coefficient decreases by 7% to 15% at low temperature, but increases by 5% to 23% at elevated temperature; crack propagation exponent increases by 7% to 21% at low temperature, but decreases by 5% to 34% at elevated temperature, compared with the situation at 25℃; hydrogen embrittlement and oxidation effects are likely to be the main reasons for more rapid crack propagation with the increasing temperature.