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Research Papers

Impact of Intensity of Residual Stress Field Upon Reyielding and Re-Autofrettage of an Autofrettaged Thick Cylinder

[+] Author and Article Information
Anthony P. Parker

Defence Academy of the United Kingdom,  University of Cranfield, Swindon, SN6 8LA, Englandparker.ETR@tiscali.co.uk

Edward Troiano

 US Army WS & T Center, Benet Labs, Watervliet, NY 12189–4050edward.troiano@us.army.mil

John H. Underwood

Battelle Scientific Services, Watervliet, NY 12189–4050treaclemine@hughes.net

J. Pressure Vessel Technol 134(4), 041003 (Jul 09, 2012) (4 pages) doi:10.1115/1.4006349 History: Received November 07, 2011; Revised January 06, 2012; Published July 09, 2012; Online July 09, 2012

Re-autofrettage has been identified as a significant, cost-effective method to achieve higher reyield pressure (RYP) and/or weight reduction in large caliber gun tubes. For a given overstrain, residual stress profiles for hydraulic and swage autofrettage may differ significantly in their intensity. The simplest representation of this “intensity” effect is the magnitude of the bending moment “locked in” via the residual hoop stress. Hill’s analytical, plane strain, Von Mises analysis predicts a larger “locked-in” moment than does the equivalent open-end condition. By assuming a range of stress-field intensities (f) scaling from 1.0 to 1.4 times that were produced by open-end hydraulic autofrettage, it was possible to assess reyield behavior following initial autofrettage via a generic numerical study. In cases where Bauschinger effect is absent, reyield initiates at the original elastic–plastic interface. This includes the ideal Hill distribution. When Bauschinger effect is present, reyield for f1.1 initiates at the bore and after further pressurization at the original elastic–plastic interface within two zones. For f1.2, the reverse is the case, with initial yield at the original elastic–plastic interface and subsequently at the bore. RYP increases with increasing f up to f = 1.175 and then decreases significantly. This loss of RYP may be mitigated by hydraulic re-autofrettage. At f = 1.0 re-autofrettage increases RYP by 4%. At f = 1.4, RYP is increased by 19%. There are modest increases in safe maximum pressure (SMP) as a result of re-autofrettage. RYP closely approaching re-autofrettage pressure is achievable for f1.3. Within this range, re-autofrettage offers a significant benefit. Re-autofrettage also produces beneficial effects via increased bore hoop compressive stress, this increase varying from 20% for f = 1% to 0% for f = 1.4. Such increased compression will benefit fatigue lifetime for fatigue cracks initiating at the bore. Conversely, tensile outside diameter (OD) hoop stress increases, with increasing f, by a maximum of 6%.

FIGURES IN THIS ARTICLE
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Copyright © 2012 by American Society of Mechanical Engineers
Topics: Stress , Autofrettage
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References

Figures

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Figure 1

(Diagrammatic) (a) original long, swaged tube; hatched lines show the position of the disk prior to extraction. (b) Intact disk after extraction. (c) Disk after axial slicing showing opening as the locked-in hoop stresses and associated bending moment are released.

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Figure 2

Residual stress profiles based upon numerical solutions (N) and analytic solutions (A). All solutions incorporate Von Mises criterion other than plane-stress case.

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Figure 3

RYP and SMP as a function of residual stress-field scaling factor (f)

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Figure 4

Von Mises stress state at peak re-autofrettage pressure of 850 MPa (f = 1.0–1.4) and for Hill at pressures of 840 MPa and 845 MPa

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Figure 5

Hoop residual stress profiles following re-autofrettage to 850 MPa

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Figure 6

Hoop stresses at inside diameter and OD before and after re-autofrettage

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