GEC ALSTHOM Engineering Systems Ltd have been involved in the design of storage tubes for spent nuclear fuel elements.
To identify candidate tube materials and welds, GEC asked TWI to carry out an experimental programme to determine the static and dynamic tensile and fracture toughness properties. TWI's 10m drop-weight tower was used for the high loading rate tests, which allowed an impact speed of up to 13400mm/s (30mph).
As expected, tensile test results showed that the strength of the steels investigated increased at higher loading rates. Fracture toughness test results on parent steels and welds revealed that an increase in loading rate causes ashift in the fracture toughness transition curve. For one steel this resulted in a change in fracture mode from fully ductile to brittle.
These results assisted GEC ALSTHOM in material selection and also demonstrated the importance of assessing design scenarios under realistic conditions. As underlined the behaviour of steel structures during recent earthquakes, fracture toughness properties are likely to be markedly less forgiving to the existence of weld flaws at high loading rates.
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