Effect of Specimen Shape on the Delayed Failure Strength of High Strength Steel Prestressed by Partial Unloading

Abstract

The effects of two types of prestressing, i.e. partial unloading and perfect unloading, on the delayed failure strength have been investigated on various specimen configurations.
The results obtained are summarized as follows:
(1) Crack initiation time and 100 h delayed failure strength can be largely increased by two types o prestress methods, especially by partial unloading method, regardless of specimen thickness and notch root radius. The rate of increase of 100 h delayed failure strength by both prestress methods increases to converge to a certain value with increase of specimen thickness.
(2) In order to raise the 100 h delayed failure strength by both prestressing methods, it is necessary to increase the unloading stress to a critical value, (σ_a)_c, which increases with increase of specimen thickness and decrease of notch root radius.