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Determining the effect of strain rate on the fracture of sheet steel
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Beaumont, Richard Adrian (2012) Determining the effect of strain rate on the fracture of sheet steel. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b2681979~S1
Abstract
A key challenge for the automotive industry is to reduce vehicle mass without
compromising on crash safety. To achieve this, it is necessary to model local failure in a
material rather than design to the overly conservative criteria of total elongation to failure.
The current understanding of local fracture is limited to quasi-static loading or strain rates
an order of magnitude too high for automotive crash applications.
This thesis studies the local fracture properties of DP800 sheet steel at the macroscopic
scale from strain rates of to for the first time. Geometries for three stress
states, namely plane-strain, shear and uniaxial tension, were developed to determine a
fracture locus for DP800 steel using optical strain measurement. These geometries were
developed using Finite Element Analysis and validated experimentally for strain rate and
stress state. Thermal imaging was used to determine the effect of strain rate on
temperature rise and its associated effect on fracture. Fractography was used to examine
the specimens’ failure modes at different strain rates.
The geometries were applied to the advanced high strength steel grade DP800. Despite
prior evidence from simple tensile test data, DP800 showed no significant variation in
fracture strain with strain rate in all three stress states. Non-contact thermal
measurements showed that the high strain rate tests ( ) were non-isothermal with
temperature rises of up to being observed. As a result of this it is difficult to
decouple the effect of strain rate from the effect of temperature and requires further
investigation. The test geometries were also applied to the deep draw steel DX54 and the
aluminium alloy AA5754 where a strain rate effect was observed. Both materials are
significantly more ductile than DP800 whish exposed a limitation in the test procedures. At
high fracture strains the stress state deviates from its intended value and can invalidate the
test. Therefore, a method was developed for determining the validity of a test for each
geometry and material from experimental data. The preliminary data from DX54 indicates
significantly greater strain rate sensitivity across one order of magnitude than was
observed in five orders of magnitude in DP800.
Item Type: | Thesis (PhD) | ||||
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Subjects: | T Technology > TA Engineering (General). Civil engineering (General) T Technology > TS Manufactures |
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Library of Congress Subject Headings (LCSH): | Sheet-steel -- Fracture, Strains and stresses | ||||
Official Date: | October 2012 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Warwick Manufacturing Group | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Dashwood, R. J.; McGregor, Iain | ||||
Sponsors: | University of Warwick; Engineering and Physical Sciences Research Council (EPSRC); Tata Steel | ||||
Extent: | xx, 201 leaves : illustrations. | ||||
Language: | eng |
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