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RESEARCH PAPERS

An Experimental-Numerical Determination of the Three-Dimensional Autofrettage Residual Stress Field Incorporating Bauschinger Effects

[+] Author and Article Information
M. Perl1

Department of Mechanical Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117576Department of Mechanical Engineering, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel

J. Perry

Department of Mechanical Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117576Department of Mechanical Engineering, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel

1

Aaron Fish Professor of Mechanical Engineering-Fracture Mechanics. On sabbatical leave from Pearlstone Center for Aeronautical Studies, Department of Mechanical Engineering, Ben-Gurion University of the Negev.

J. Pressure Vessel Technol 128(2), 173-178 (Dec 12, 2005) (6 pages) doi:10.1115/1.2172959 History: Received November 23, 2005; Revised December 12, 2005

Autofrettage of large-caliber gun barrels is used to increase the elastic strength of the tube and is based on the permanent expansion of the cylinder bore, using either hydraulic pressure or an oversized swage mandrel. The theoretical solution of the autofrettage problem involves different yield criteria, the Bauschinger effect, and the recalculation of the residual stress field post barrel’s machining. Accurate stress-strain data and their appropriate numerical representations are needed as input for the numerical analysis of the residual stress field due to autofrettage. The purpose of the present work is to develop a three-dimensional (3D) numerical solution for both the hydraulic and the swage autofrettage processes incorporating the Bauschinger effect, using an accurate numerical representation of the experimentally measured material behavior. The new 3D computer code that was developed is capable of determining the stresses, strains, displacements, and forces throughout the entire autofrettage process. The numerical results were validated by an instrumented standard swage autofrettage process. The numerical model was found to excellently reproduce the experimentally measured pushing force as well as the permanent bore enlargement of the barrel. The calculated tangential stresses and the measured ones follow a similar pattern, but their numerical magnitude differs considerably. A wide discrepancy in both pattern and magnitude was found between the calculated and the measured axial stresses. These discrepancies seem to stem from the exact details of the mandrel’s insertion into the tube and are now under further investigation. However, in order to further validate the numerical code an hydraulic autofrettage experiment will be performed, which will hopefully eliminate the swage autofrettage discrepancies.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 2

The cylinder’s geometry–annular-strip grid

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Figure 3

The four stages of the autofrettage process

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Figure 4

The universal tensile stress-strain curve

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Figure 1

Simulation of the mandrel’s pushing force in swage autofrettage

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Figure 5

Young’s modulus Bauschinger effect factor

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Figure 6

Yield stress Bauschinger effect factor

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Figure 7

The universal compressive stress-strain curve

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Figure 8

The residual stresses following unloading

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Figure 9

The final residual stress field after machining

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Figure 10

Yield stress Bauschinger effect factor in tension

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Figure 11

The mandrel’s pushing force along the distinct barrel’s zones

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Figure 12

The experimental and numerical strains as a function of the mandrel’s location

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