Proof testing — the effects of slow crack growth

Abstract

When slow crack growth occurs during proof testing, the extent of the crack growth while unloading from the proof stress has a substantial effect on the minimum predicted in-service failure time. It is essential that this crack growth is minimized to achieve effective failure prediction. Analyses are presented which show that the detrimental effects can be negated by environmental control during proof testing and/or rapid unloading from the proof stress; the requisite combination of unloading rate and environmental control is determinated separately for each system.