FATIGUE LIFE AND CRACK RESISTANCE OF SHEET AL-LI 1460 ALLOY AT 293-K TO 4-K

The fatigue life and fatigue crack growth rate of Al-Li 1460-T8 alloy under cyclic tension (asymmetry coefficient R = 0.1) are studied on fl at samples at T = 293 K (air), 77 K (liquid nitrogen), 20 K (liquid hy drogen and hydrogen vapour), and 4 K (liquid helium). The fractured sa mples are examined macrofractographically and electron-fractographical ly. It is found that at temperature lowering from 293 K to 4 K the fat igue life increases and the fatigue crack growth slows down. The monot onicity of these temperature dependences is disturbed at 20 K in liqui d hydrogen: in this medium the fatigue life either decreases or coinci des with that in liquid nitrogen (77 K) depending on the stress amplit ude; a similar decrease under these conditions is also observed for th e crack growth rate. Proceeding from macro- and microfractographic dat a, the correlation is found between fatigue life, crack growth rate an d fracture mechanisms in different cryogenic media. Possible mechanism s of temperature and liquid hydrogen medium effects upon the fatigue c haracteristics of the 1460 alloy are considered.