Determination of true stress strain characteristics of structural steels using Instantaneous Area Method

This paper presents recent research findings on true stress strain characteristics of normal strength S275, S355 and high strength S690 steels to EN 10025:2005. It aims to provide generalized constitutive models for analysis and design of steel structures. Comprehensive experimental and numerical investigations into mechanical properties of the structural steels have been carried out based on test results of nine monotonic tensile tests. Non-uniform stress and strain distributions within the necked region are found when the test coupons are under very large deformation. After corrections to the stress and strain non-uniformities by Instantaneous Area Method with successive approximations, true stress strain characteristics of the tested steels were successfully quantified as generalized constitutive models. Moreover, the microstructures of the typical structural steels haven been carefully examined, and their microstructural constituents are successfully quantified by Digital Image Analytics. The research findings are very important for subsequent numerical investigations into the structural performance of steel structures under very large deformations up to fracture. The authors are grateful for the financial supports from the Research Grants Council of the Government of Hong Kong SAR, and the CNERC for Steel Construction (HKB).