Geometrical and Material Characterization of Quenched and Self-Tempered Steel Reinforcement Bars
Publication: Journal of Materials in Civil Engineering
Volume 28, Issue 6
Abstract
Quenched and self-tempered (QST) steel reinforcement bars (rebars) are manufactured by Thermex or Tempcore processes. Characterization studies of QST rebars are mostly limited to reveal the hardened outer layer and some improved mechanical properties compared to hot-rolled (HR) and cold-worked (CW) rebars. However, investigations on residual stresses and imperfections originating from the manufacturing process as well as stress concentrations arising from the ribbed profile are rarely found in the literature. Surface residual stress may be beneficial or detrimental to the fatigue performance of rebars although they have been studied only on the subsurface of QST rebars. Surface imperfections are zones of stress concentration from where fatigue cracks may initiate. Imperfections are usually identified in the fractured cross section resultant from fatigue tests of rebars. Stress concentrations can also arise from the rib geometry. Although the rib geometric parameters affect the stress concentration factor on rebars, stress concentration analysis are restricted to two-dimensional (2D) finite-element models (FEMs). The study presented herein is part of a further detailed investigation on the fatigue behavior of HR-CW and QST rebars in the very high cycle domain. In the present work, characterization analyses of QST rebars include (1) experimental investigation of surface and subsurface residual stresses on QST rebars by cut compliance and X-ray diffraction techniques (residual stresses from both techniques are discussed); (2) identification of surface imperfections by scanning electron microscopy (SEM) analysis; and (3) three-dimensional (3D) finite-element analysis of stress concentrations on the ribbed profile. The influence of the rib geometry such as radius, width, height, and inclination as well as the rebar diameter on values are analyzed. The critical zones are determined along the ribs.
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Acknowledgments
The authors are grateful to Danièle Laub from the Interdisciplinary Centre for Electron Microscopy (CIME) at EPFL for her help with the sample preparation for the microscopic analyses. We are also grateful to Cyril Dénéréaz from the Mechanical Metallurgy Laboratory (LMM) for the hardness measurements.
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Published In
Journal of Materials in Civil Engineering
Volume 28 • Issue 6 • June 2016
Copyright
© 2016 American Society of Civil Engineers.
History
Received: Sep 5, 2014
Accepted: Apr 8, 2015
Published online: Jan 7, 2016
Published in print: Jun 1, 2016
Discussion open until: Jun 7, 2016
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