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The molecular wedge in brittle cracks

1988; Pergamon Press; Volume: 22; Issue: 3 Linguagem: Inglês

10.1016/s0036-9748(88)80210-2

1878-2663

Robb Thomson,

Ultrasonics and Acoustic Wave Propagation

Sustained-loading crack growth has been observed in two experimental AlLi alloys at 20 and 80 °C in circumstances where there is no strong connection between fracture and conventional stress corrosion cracking or hydrogen embrittlement. The simple ternary alloy examined (AlLiZr) was found to be much more susceptible to slow crack growth than the more complex alloy (AlLiCuMgZr) which contains additional hardening precipitates. This difference is associated with the different creep response of the alloys. Water vapour in the atmosphere was found to assist crack growth in the simple ternary alloys, but a consideration of equilibrium conditions at the crack tip shows that the crack tips are “dry” in all atmospheres apart from water-saturated air. Assistance of slow crack growth by the adsorption of water molecules is considered in terms of the formation of a Thomson-type molecular wedge.