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Research Papers: Materials and Fabrication

A Study of the Combined Effects of Erosions, Cracks and Partial Autofrettage on the Stress Intensity Factors of a Thick Walled Pressurized Cylinder

[+] Author and Article Information
Q. Ma

Edward F. Cross School of Engineering,
Walla Walla University,
College Place, WA 99324

C. Levy

Fellow, ASME
Department of Mechanical
and Materials Engineering,
Florida International University,
Miami, FL 33199

M. Perl

Fellow, ASME
Pearlstone Center for Aeronautical
Engineering Studies,
Department of Mechanical Engineering,
Ben Gurion University of the Negev,
Beer Sheva 84105, Israel

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the Journal of Pressure Vessel Technology. Manuscript received July 22, 2012; final manuscript received January 17, 2013; published online June 11, 2013. Assoc. Editor: Kunio Hasegawa.

J. Pressure Vessel Technol 135(4), 041403 (Jun 11, 2013) (8 pages) Paper No: PVT-12-1099; doi: 10.1115/1.4023732 History: Received July 22, 2012; Revised January 17, 2013

For the investigation of cracked problems in thick-walled pressurized cylindrical vessels, the displacement-based finite element method has become one of the main computational tools to extract stress intensity results for their fatigue life predictions. The process of autofrettage, practically from the partial autofrettage level of 30% to full autofrettage level of 100%, is known to introduce favorable compressive residual hoop stresses at the cylinder bore in order to increase its service life. In order to extract the fatigue life, stress intensity factors (SIFs) need to be obtained a priori. The necessity for determining SIFs and their practical importance are well understood. However, it is usually not a trivial task to obtain the SIFs required since the SIFs largely depend on not only the external loading scenarios, but also the geometrical configurations of the cylinder. Our recent work has shown that the Bauschinger effect (BE) may come into play and affect the effective SIFs significantly for an eroded fully autofrettaged thick-walled cylinder. In this study, we further investigate the SIFs for the Bauschinger effect dependent autofrettage (BEDA) and the Bauschinger effect independent autofrettage (BEIA) at various autofrettage levels. The crack is considered to emanate from the erosion's deepest point in a multiply eroded cylinder. The commercial finite element package, ANSYS v12, was employed to perform the necessary analysis. A two-dimensional model, analogous to the authors' previous studies, has been adopted for this investigation. The residual stress field of autofrettage process, based on von Mises yield criterion, is simulated by thermal loading. The combined SIFs are evaluated for a variety of relative crack lengths with cracks emanating from the tip of erosions with various geometrical configurations and span angles. The effective SIFs for relatively short cracks are found to be increased by the presence of the erosion and further increased due to the BE at the same autofrettage level, which may result in a significant decrease in the vessel's fatigue life. Deep cracks are found to be almost unaffected by the erosion, but may be considerably affected by BE as well as by the level of partial autofrettage.

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Figures

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Fig. 1

Model of a multiply eroded cracked cylinder with three erosions and one edge crack

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Fig. 2

Erosion configurations (a) semicircular erosion (b) arc erosion (c) elliptic erosion

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Fig. 3

Absolute normalized autofrettage SIF versus nomalized erosion depth considering a constant crack depth a0/t = 0.05

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Fig. 4

Absolute normalized autofrettage SIF versus normalized crack depth considering a constant erosion depth d/t = 0.05

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Fig. 5

Normalized effective SIF versus normalized crack depth with d/t = 0.05, d/h = 1, and n = 1

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Fig. 6

Autofrettage efficiency versus normalized crack depth with d/t = 0.05, d/h = 1, and n = 1

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Fig. 7

Normalized effective SIF versus normalized crack depth with one arc erosion d/t = 0.05, r ′/t = 0.1, and n = 1

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Fig. 8

Normalized effective SIF versus erosion ellipticity with a very shallow crack (d/t = 0.05, a0/t tends to 0 and n = 1)

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Fig. 9

Normalized effective SIF versus erosion ellipticity with d/t = 0.05, a0/t = 0.05, and n = 1

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Fig. 10

Normalized effective SIF versus normalized erosion depth with a0/t = 0.05, d/h = 1, and n = 1

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Fig. 11

The normalized effective SIF versus erosion span angle for the one edge crack and three erosions with d/t = 0.05, d/h = 1, and a0/t = 0.05

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