Creep

Under stress at high temperatures (750DEG-1,000DEG F.), most metals, even hard alloy steels, manifest a sort of internal slip or "creep." To prevent costly machine failures and ugly accidents, metallurgists have long studied, measured and allowed for creep, but they still do not know much about what fundamentally happens.

Last week the metallurgical journal Metal Progress commented on the researches of Professor Daniel Hanson of England's University of Birmingham, who had divided creep into four stages. These are elastic stretch (like rubber); plastic flow (like mud); slower plastic flow; approach to fracture. Professor Hanson's theory of fracture is that the metal atoms, under continuing mechanical stress plus their own agitation due to heat, are moved one by one to new positions so that the whole structure is weakened. When enough atoms are thus individually moved, the metal breaks.

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