NOVEL METHODS FOR DETERMINING TRUE STRESS STRAIN CURVES OF WELDMENTS AND HOMOGENOUS MATERIALS

摘要

This paper presents two new methods, one for weldments, and one for homogenous materials, for determining a material's whole range true tress - logarithmic strain curve, including both the pre- and post- plastic localization regimes. A material's whole range true stress-strain curve is of crucial importance for plastic forming analysis, and also for the analyses of damage and ductile fracture, where large plastic deformation is involved. For homogenous materials, only smooth round tensile specimens are used for determining the true stress strain curve. In many cases, it is demanding to use rectangular tensile specimens. Recently, an extensive study has been carried out by the authors on the diffuse necking behavior of specimens with rectangular cross section. It is found that the material's true stress-strain relation can be determined from the load versus thickness reduction curve of a rectangular specimen. An approximate equation for calculating true area reduction from thickness reduction for different materials and aspect ratio, is given. For weldments the conventional cross weld tensile specimens give practically little useful information. A novel method is developed for determining the true stress-strain curves of different material zones of a weldment, by using notched cross weld tensile specimens. The method can be applied to determine the true stress-strain curves for base metal, weld metal and HAZ. The effects of various parameters on the accuracy of both methods has been investigated.