A special notched tensile specimen to determine the flow stress-strain curve of hardening materials without applying the Bridgman correction

Abstract

Structural integrity assessment of weldments requires the input of flow stress-strain curve of each individual material zone. To cope with these challenges, a cylindrical cross weld tensile specimen with a notch located either in the weld metal, base metal or possibly heat affected zone has been previously developed by the authors to determine the true stress-strain curve for the material zone of interest. The disadvantage of this notched tensile testing method as well as the standard tensile testing method using a smooth specimen, is that the well-known Bridgman correction still has to be applied in order to obtain material’s equivalent or flow stress-strain curves. In this study, tensile specimens with various notch geometries have been scrutinized and a ‘magic’ specimen with a special notch geometry has been identified. By using this special notched tensile specimen, material’s flow stress-strain curve can be directly calculated from the recorded load versus diameter reduction curve and no Bridgman correction is needed. The method is very accurate for power-law hardening materials and becomes less accurate for materials with significant Lüders plateau in the initial yield region.