ABSTRACT
Creep tests can be carried out at constant load or at constant stress. The use of a constant load implies an increasing stress as the cross-section of the sample decreases during the creep tests. The constant-load curve exhibits an instantaneous elongation which is made up of elastic, anelastic and plastic components followed by a period of decelerating creep, one of steady-state creep, then accelerated creep and eventually fracture. The occurrence of accelerated creep under constant load is due in part to the fact that the stress is increasing. The division of the creep curve into primary, secondary and tertiary regions dates back to the work of E. N. Andrade who first analysed the process of creep. The need to extrapolate the results of accelerated creep tests has been met by the development of several methods. A simpler approach is the F. C. Monkman-N. J. Grant relationship, which states that for given material in a certain range of stress and strain.
