The Effect Of Pre-Strain And Aging On The Fracture Toughness Of Australasian Constructional Mild Steel

Hyland, C. W. K., Ferguson, W. G. and Butterworth, J. W. (2004). The Effect Of Pre-Strain And Aging On The Fracture Toughness Of Australasian Constructional Mild Steel. In: Atrens, A., Boland, J. N., Clegg, R. and Griffiths, J. R., Structural Integrity and Fracture International Conference (SIF'04), Brisbane, Australia, (163-170). 26-29 September 2004.

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Author Hyland, C. W. K.
Ferguson, W. G.
Butterworth, J. W.
Title of paper The Effect Of Pre-Strain And Aging On The Fracture Toughness Of Australasian Constructional Mild Steel
Conference name Structural Integrity and Fracture International Conference (SIF'04)
Conference location Brisbane, Australia
Conference dates 26-29 September 2004
Publication Year 2004
Sub-type Fully published paper
Editor Atrens, A.
Boland, J. N.
Clegg, R.
Griffiths, J. R.
Start page 163
End page 170
Abstract/Summary The effect of tensile pre-strain and aging on the brittleness of mild steel at typical building service temperatures was investigated. Brittle cleavage modes of fracture were developed at temperatures as high as 10 and 20 degree C in side-grooved CTOD specimens, that had been prepared from steel pre-strained by 9.8% or more. The CTOD three-point bend samples, SENB3, were cut from 25 mm thick flanges of 310UC158 Grade 300Plus steel column sections and were naturally aged for 11 months or more after pre-straining. The effect of natural aging was more pronounced than expected, significantly raising the tensile properties of the pre-strained steel. The fracture properties of the steel were also affected by the combination of pre-strain and aging. Steel that had been pre-strained by 4.9% and aged showed the greatest increase in fracture toughness, compared to as-received steel, and failed by ductile fibrous fracture at 10 degree C. Steel that had been pre-strained by 9.8% and 17.7% and then aged, exhibited a smaller increase in fracture toughness. At 10 and 20 degree C this more highly pre-strained steel failed by brittle cleavage fracture, while at 30 degree C failure was by ductile fibrous fracture. Examination of the fracture surfaces by scanning electron microscope indicated that cleavage fracture in the aged pre-strained steel was influenced by the density of non-metallic inclusions. The effect of the development of brittle cleavage modes of fracture in the pre-strained and aged steel at typical building service temperatures requires further investigation to assess the implications on structural integrity of pre-strains introduced during fabrication and those caused by design events such as earthquakes and explosive blasts. The study also found that the Direct Current Potential Drop method, DCPD, of determining fracture initiation and therefore fracture properties, was more effective than the single specimen test procedure specified in BS7448-4:1997. All the specimens tested exhibited Type 4 or Type 6 force versus displacement characteristics according to BS 7448:Part1:1991. The fracture initiation values, delta i , identified by the DCPD method were in reasonable agreement with the delta u values calculated using BS 7448:Part1:1991, for the specimens that showed Type 4 characteristics. However the delta m values calculated for specimens with Type 6 characteristics using BS 7448:Part1:1991, significantly over-predicted the CTOD at initiation, compared to that found using the DCPD method.
Subjects 290801 Structural Engineering
Keyword fracture
mild steel
pre-strain
aging
Australasian
brittleness
cleavage
Q-Index Code E1
Q-Index Status Provisional Code
Institutional Status Unknown

Document type: Conference Paper
Collection: School of Mechanical & Mining Engineering Publications
 
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Created: Mon, 20 Dec 2004, 10:00:00 EST by Lucy Peachey on behalf of Research Management Office