Aluminium crack propagation

In more recent work embrittlement in water vapour-saturated air and in various aqueous solutions has been systematically examined together with the influence of strain rate, alloy composition and loading mode, all in conjunction with various metallographic techniques. The general conclusion is that stress-corrosion crack propagation in aluminium alloys under open circuit conditions is mainly caused by hydrogen embrittlement, but that there is a component of the fracture process that is caused by dissolution. The relative importance of these two processes may well vary between alloys of different composition or even between specimens of an alloy that have been heat treated differently. 

Remarkably little has been published on corrosion fatigue crack propagation in copper and its alloys. In general little or no influence of marine environments has been observed in crack propagation experiments on manganese and nickel-aluminium bronzes although the frequencies employed were quite high (> 2.5 Hz) ... 

Fig. 8.64 Micrograph of a bridging site taken in situ in the SEM (secondary electrons) during crack propagation in an alumina/ aluminium titanate. P and Q denote frictions points during grain pull-out (courtesy of Nitin Padture) [21]. With kind permission of Dr. Jorge Lino...

In the case of aluminium alloys, propagation of stress corrosion cracks always proceeds along grain boundaries this form of corrosion is sometimes considered as a special case of intercrystalline corrosion in which mechanical stress accelerates crack propagation along grain boundaries. 

Wang, Kwei and Zupko have described experiments carried out on butt-jointed epoxy-aluminium plates which contained single cracks at the centre of the bond surface. They used the results of Sih and RicelS and ErdoganlS to show that the stress intensity factors for crack propagation are given by... 

Equipment and pipes within the coldbox are made of aluminium alloy or 18/10-CrNi-steel. These materials are suitable for the application at low temperatures and dispose high ductihty even at 100 K, i.e. no tendency to propagation of cracks, originating from notches, sharp edges or abrupt discontinuities of the wall thickness. 

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