Stress-Relaxation Behaviour of Chromium-Molybdenum and Chromium-Molybdenum-Vanadium Bolting Materials

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Abstract
The object of this paper is to illustrate by means of a series of tests made on two steels, the essential differences between testing under constant load, constant total strain, and a commonly used ‘weighbar’ method that is intermediate between these two. It shows that the constant strain results do not entirely support the strain-hardening and time-hardening theories suggested by other authors. An empirical relationship, which gives reasonable correlation in the ranges of stress, temperature, and time examined, is given as an aid to analysing the results, but no correlation of this with a theoretical approach has been found, though it is hoped that it will contribute to the eventual solution of this problem. Suggestions are finally made as to how relaxation data may be used for design purposes with reference particularly to the choice of an initial stress and the value of retightening.

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