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12.13: On recent characterisations of the post‐yield properties of structural carbon steels
Author(s) -
Sadowski Adam J.,
Rotter J. Michael,
Ummenhofer Thomas
Publication year - 2017
Publication title -
ce/papers
Language(s) - English
Resource type - Journals
ISSN - 2509-7075
DOI - 10.1002/cepa.413
Subject(s) - strain hardening exponent , hardening (computing) , structural engineering , materials science , finite element method , carbon steel , ultimate tensile strength , forensic engineering , metallurgy , composite material , engineering , corrosion , layer (electronics)
New design methodologies are being developed that permit the full plastic condition and strain hardening properties of steel members and structures to be exploited. However, it has long been recognised that even the full plastic moment of a cross‐section cannot be attained assuming only an ideal elastic‐plastic material law, since infinite curvatures would be required to do so. Further, tests on structural members routinely show that, due to strain hardening, the full plastic condition is exceeded at finite slendernesses where one might expect stability to affect the result. This indicates that strain hardening should be a key consideration in design. Unfortunately, the strain hardening properties of carbon steels are not guaranteed by any standard or steel manufacturer, and no reliable depository of information is known to exist. Similarly, the proliferation of powerful modern finite element software that can handle significant geometric and material complexities is at odds with the paucity of information available to the analyst on the reliable choice of post‐yield material properties for carbon steels. This paper presents a brief overview of the results presented in recent publications by the authors that attempt to tackle this problem. The intention is to alert the structural engineering community to the wealth of information contained in a typical tensile stress‐strain curve relationship beyond that which is commonly reported, and to show the tentative progress that has been made in characterising the post‐yield properties of some of the most common structural steels. A specialised algebraic formulation is used to process a database of 225 stress‐strain curves of various grades, allowing an accurate assessment of their post‐yield material properties. These include the length and gradient of the yield plateau, the initial tangent strain hardening modulus of the post‐plateau region, and preliminary statistical bounds for these for the most common grades. The paper additionally flags the novel notion that the yield plateau itself exhibits a small but finite and statistically significant positive gradient, which is potentially important in structural resistance calculations.