M. Fonte

The microstructure and environment influence on fatigue crack growth in 7049 aluminum alloy at different load ratios

Abstract The role of microstructure and environmental influence on fatigue crack has been investigated on a high strength 7049 aluminium alloy, artificially aged to underaged (UA) and overaged (OA) microstructures with approximately the same yield strength properties, but differing in the mode of slip deformation. The UA alloy deforms by planar slip while the OA alloy by wavy slip. Crack growth measurements were performed at constant load ratios, between 0.8 and −1, in ambient air and vacuum. The influence of load ratio is discussed in terms of slip deformation mechanisms, microstructure, and the influence of environment using the two intrinsic parameters, ΔK and Kmax.

The environment effect on fatigue crack growth rates in 7049 aluminium alloy at different load ratios

Abstract The influence of environment and micro structure is investigated on a high strength 7049 aluminium alloy sheet cold rolled and heat-treated. This aluminium alloy was artificially aged to underaged (UA) and overaged (OA) conditions, resulting in approximately the same yield strength, but different mode of slip deformation. The UA alloy deforms by planar slip while the OA alloy by wavy slip. Crack growth measurements were performed at constant load ratios between -1 and 0.8 in ambient air and vacuum. The influence of load ratio is discussed in terms of slip deformation mechanisms, microstructure and environmental effects using the two intrinsic parameters, ΔK and K max The two parameters lead to two intrinsic thresholds that must be simultaneously exceeded for a fatigue crack growth. Mechanisms of near-threshold crack growth are briefly discussed for several concurrent processes involving environmentally assisted cracking with intrinsic microstructural effects.