Abstract
Fatigue crack growth (FCG) properties were determined for aluminum alloy 6061-T6 and 7075-T6 plates exposed to a humid (relative humidity RH=90%) air or dry nitrogen gas, and the effect of hydrogen on the FCG process was discussed together with a fractographic study of fracture surfaces. The 6061-T6 shows a superior FCG resistance to the 7075-T6, resulting in no increase in FCG rate with a reduction of frequency from 10 Hz to 0.1 Hz and also with a change of cyclic loading wave from sine to trapezoid. This response is attributed to the effect of hydrogen to assist localized slip deformation, leading to a crack-tip bunting. According to applying the present FCG data to design a high-pressure container liner for automobile on a basis of the engineering standard JARI S001, it is found that the 6061-T6 can possess a higher allowable stress than the 7075-T6.
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