Determining material true stress-strain curve from tensile specimens with rectangular cross-section

The uniaxial true stress logarithmic strain curve for a thick section can b e determined from the load-diameter reduction record of a round tensile spe cimen. The correction of the true stress for necking can be performed by us ing the well-known Bridgman equation. For thin sections, it is more practic al to use specimens with rectangular cross-section. However, there is no es tablished method to determine the complete true stress-logarithmic strain r elation from a rectangular specimen. In this paper, an extensive three-dime nsional numerical study has been carried out on the diffuse necking behavio ur of tensile specimens made of isotropic materials with rectangular cross- section,and an approximate relation is established between the area reducti on of the minimum cross-section and the measured thickness reduction. It is found that the area reduction can be normalized by the uniaxial strain at maximum load which represents the material hardening and also the section a spect ratio. Furthermore, for the same material, specimens with different a spect ratio give exactly the same true average stress-logarithmic strain cu rve. This finding implies that Bridgman's correction can still be used for necking correction of the true average stress obtained from rectangular spe cimens. Based on this finding, a method for determining the true stress-log arithmic strain relation from the load-thickness reduction curve of specime ns with rectangular cross-section is proposed. (C) 1999 Elsevier Science Lt d. All rights reserved.