NDLI: Prediction of Ratchet Boundary for 90-Degree Smooth and Mitred Pipe Bends

Content Provider	The American Society of Mechanical Engineers (ASME) Digital Collection
Author	Ahmed, G. Korba Mohammad, M. Megahed Hany, F. Abdalla Mohamed, M. Nassar
Copyright Year	2012
Abstract	The present paper attempts to predict ratchet boundary for 90-degree mitred and smooth pipe bends subjected to sustained pressure and cyclic in-plane bending. The methodology utilizes a recently published technique known as the “Uniform Modified Yielding” (UMY) technique, which relies on generation of a virtual structure with inhomogeneous reduced yield strength, whose magnitude and distribution depend on the elastic stress field due to the cyclic load. The collapse load of this virtual structure determines the threshold steady load necessary for commencement of “incremental collapse”. The technique is applied first to predict ratchet boundaries for two benchmark problems possessing analytical descriptions of ratchet boundary and uni-axial states of stress; the two-bar structure problem and the Bree cylinder. Predicted ratchet boundaries exactly coincided with the corresponding published analytical descriptions, and reasons for this correlation were discussed in this paper. The technique was then applied to three 90-degree pipe bends with similar geometries as follows: smooth pipe bend (SPB), single mitred pipe bend (SMPB), and three weld mitred pipe bend (3WMPB). Certain assumptions are adopted to enable treatment of the problem as a quasi-uniaxial one. Conservative estimates are obtained for ratchet boundaries in pipe bends that correlates well with elastic shakedown/ratchet boundary of the same problems as predicted by a recently developed non-cyclic direct technique.
Sponsorship	Pressure Vessels and Piping Division
Starting Page	617
Ending Page	626
Page Count	10
File Format	PDF
ISBN	9780791855027
DOI	10.1115/PVP2012-78673
Volume Number	Volume 3: Design and Analysis
Conference Proceedings	ASME 2012 Pressure Vessels and Piping Conference
Language	English
Publisher Date	2012-07-15
Publisher Place	Toronto, Ontario, Canada
Access Restriction	Subscribed
Subject Keyword	Collapse Yield strength Pipe bends Pressure Stress Cylinders
Content Type	Text
Resource Type	Article

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