Abstract
The fatigue life and fatigue crack growth rate of AlLi 1460-T8 alloy under cyclic tension (asymmetry coefficient R = 0.1) are studied on flat samples at T = 293 K (air), 77 K (liquid nitrogen), 20 K (liquid hydrogen and hydrogen vapour), and 4 K (liquid helium). The fractured samples are examined macrofractographically and electron-fractographically. It is found that at temperature lowering from 293 K to 4 K the fatigue life increases and the fatigue crack growth slows down. The monotonicity of these temperature dependence is disturbed at 20 K in liquid hydrogen: in this medium the fatigue life either decreases or coincides with that in liquid nitrogen (17 K) depending on the stress amplitude; a similar decrease under these conditions is also observed for the crack growth rate. Proceeding from macro- and microfractographic data, the correlation is found between fatigue life, crack growth rate and fracture mechanisms in different cryogenic media. Possible mechanisms of temperature and liquid hydrogen medium effects upon the fatigue characteristics of the 1460 alloy are considered.
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