Abstract
Recent experiments on pressure vessel steels have shown that the fracture toughness can be significantly increased at low temperatures if the material is prestressed at a higher temperature. A conservative method is formulated to use this warm prestressing effect in the fracture mechanics analysis of nuclear pressure vessels under thermal shock. This method uses the basic premise that a crack will not initiate when the stress intensity factor is dropping with time (or constant), whether or not the temperature is dropping. A considerable amount of supportive experimental information is presented and a thorough justification of the method is given. One example is presented to illustrate the beneficial aspects of warm prestressing during a thermal shock. The results show that, when warm prestressing is used, the minimum initiation crack depth can be greater, in some cases, by a factor of ten than that calculated by standard methods.
Published Version
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