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Research Papers: Design and Analysis

Plastic Instabilities in Spherical Vessels for Static and Dynamic Loading

[+] Author and Article Information
T. A. Duffey

P.O. Box 1239, Tijeras, NM 87059tduffey2@aol.com

Impulsive loading is defined in ASME Code Case 2564 as a loading whose duration is less than 35% of the fundamental breathing mode of the vessel.

J. Pressure Vessel Technol 133(5), 051210 (Jul 15, 2011) (6 pages) doi:10.1115/1.4003472 History: Received September 27, 2010; Revised December 21, 2010; Published July 15, 2011; Online July 15, 2011

Significant changes were made in design limits for pressurized vessels in the 2007 version of the ASME code (Sec. VIII, Div. 3) and 2008 and 2009 Addenda, and these are now a part of the 2010 code. There is now a local damage-mechanics based strain-exhaustion limit, including the well-known global plastic collapse limit. Moreover, Code Case 2564 (Sec. VIII, Div. 3) has recently been approved to address impulsively loaded vessels. It is the purpose of this paper to investigate the plastic collapse limit as it applies to dynamically loaded spherical vessels. Plastic instabilities that could potentially develop in spherical shells under symmetric loading conditions are examined for a variety of plastic constitutive relations. First, literature survey of both static and dynamic instabilities associated with spherical shells is presented. Then, a general plastic instability condition for spherical shells subjected to displacement-controlled and short-duration dynamic pressure loading is given. This instability condition is evaluated for six plastic and viscoplastic constitutive relations. The role of strain rate sensitivity on the instability point is investigated. Conclusions of this work are that there are two fundamental types of instabilities associated with failure of spherical shells. In the case of impulsively loaded vessels, where the pulse duration is short compared with the fundamental period of the structure, one instability type is found not to occur in the absence of static internal pressure. Moreover, it is found that the specific role of strain rate sensitivity on the instability strain depends on the form of the constitutive relation assumed.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

Grahic Jump Location
Figure 1

Coordinates of spherical shell

Grahic Jump Location
Figure 2

Structural and material instabilities for a spherical shell with bilinear stress-strain relation and σ0/K=0.1

Grahic Jump Location
Figure 3

Hoop force as a function of radial displacement, for example, problem utilized in Ref. 9

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