Crack growth in aluminium cylinders

Some common portable aluminium gas cylinders have shown a tendency to devel op cracking. This cracking has in some cases led to leaks and on occasions to violent and sometimes fatal failures. There are a number of features of this cracking which have not been explained properly, Previous estimates of the growth rate of these cracks under sustained load have been developed from specimen testing. As shown in this paper these dat a predict crack growth rates which are too slow, by very large factors, whe n considered in light of actual failures that have been observed. It also a ppears that crack growth can be rapid even in cylinders with low levels of lead. This paper presents a numerical simulation of the growth of cracks in alumi nium cylinders based on local stresses in vicinity of crack edge. This info rmation is related to cracks actually found in cylinders that have leaked o r failed in service. From this procedure an equation for the crack growth r ate is developed which is much higher that that determined from small speci men testing. This paper concludes that additional factors, which have not b een replicated adequately in testing, must influence crack growth rates. (C ) 2001 Elsevier Science Ltd. All rights reserved.