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Research Papers: Materials and Fabrication

On the Material Modeling of the Autofrettaged Pressure Vessel Steels

[+] Author and Article Information
G. H. Farrahi

School of Mechanical Engineering, Sharif University of Technology, Tehran 11365-8639, Iranfarrahi@sharif.edu

E. Hosseinian

School of Mechanical Engineering, Sharif University of Technology, Tehran 11365-8639, Iranehs@mehr.sharif.edu

A. Assempour

School of Mechanical Engineering, Sharif University of Technology, Tehran 11365-8639, Iranassem@sharif.edu

J. Pressure Vessel Technol 131(5), 051403 (Jul 27, 2009) (6 pages) doi:10.1115/1.3148084 History: Received September 07, 2008; Revised March 18, 2009; Published July 27, 2009

Material modeling of high strength steels plays an important role in the accurate analysis of autofrettaged tubes. Although, the loading behavior of such materials is nearly elastic-perfectly plastic, their unloading behavior due to Bauschinger effect is very complicated. DIN1.6959 steel is frequently used for construction of autofrettaged tubes in some countries such as Germany and Switzerland. In spite of similarity between chemical compositions of this steel with that of A723 steel, due to different material processing, these two steels have an unlikely behavior. In this paper the material behavior of DIN1.6959 was accurately modeled by uniaxial tension-compression test results. Both 6 mm and 12.5 mm diameter specimens were used and compared. Also various relations for modeling of autofrettaged steels were investigated, and a new relation was introduced for accurate modeling. Moreover, two test methods, i.e., uniaxial tension-compression and torsion tests, used for modeling of autofrettage steels, were analyzed. Also, material models of three important autofrettage steels, i.e., A723, HB7, and DIN1.6959, were compared.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Configuration of a 12.5 mm diameter test specimen

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Figure 2

Engineering stress-strain plots of DIN1.6959

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Figure 3

Typical uniaxial stress-strain curve showing loading and unloading regimes

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Figure 4

Experimental data and proposed fit for normalized unloading Young’s modulus of DIN1.6959 steel

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Figure 5

Normalized unloading Young’s modulus; comparison between A723, DIN1.6959, and HB7 steels

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Figure 6

Bauschinger effect factor of DIN1.6959 versus initial plastic strain; comparison between various offset values and proposed fits

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Figure 7

Bauschinger effect factor versus initial plastic strain; comparison between A723, DIN1.6959, and HB7 steels

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Figure 8

Full material model of DIN1.6959; comparison between experimental data and numerical fits

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Figure 9

Comparison between uniaxial tension-compression test and torsion test results

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Figure 10

Normalized Young’s modulus; comparison between uniaxial tension-compression and torsion tests

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Figure 11

Bauschinger effect factor (0.2% offset value); comparison between uniaxial and torsion tests

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