Stress Distribution in Concentrically-Hollowed Thick-Walled Tubes Subjected to Uniform Radial Loading.
ARMY ARMAMENT RESEARCH DEVELOPMENT AND ENGINEERING CENTER WATERVLIET NY BENET LABS
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Autofrettage is a manufacturing process whereby a thick-walled cylindrical pressure vessel is pressurized well beyond its elastic limit. This pressurization causes the tubes interior to undergo plastic deformation. Under such a loading, the radial component of the stress throughout the tubes wall thickness is compressive, while the tangential component is mainly tensile. In very thick-walled tubes with a significant plastically deformed inner sleeve, the tangential stress component near the bore may also become compressive. However, upon depressurization, both the radial and the tangential components of the stress near the tubes bore are compressive. Likewise, the stress distribution throughout the wall thickness of a press-fitted liner inside a thick-walled tube is compressive for both the radial and tangential components. It has long been established that autofrettage of a pressure vessel, before putting it into service, increases its fatigue life. However, the optimal amount of autofrettaging is not clear. Furthermore, it is not clear to this investigator how much of the improvement in fatigue life is due to the post-autofrettage compressive tangential stresses at the bore, and how much is due to the small plastic deformation that takes place near the bore under compressive hydrostatic stresses. The ability to compute the stress distribution during autofrettage and after depressurization can be useful in determining autofrettage optimization. Furthermore, the ability to correlate the elastic-plastic interface and the state of stress on that surface, due to known stresses at the bore andor radial stresses at the tubes outer diameter, facilitates the means for predicting the interfacial radial stress between two concentrically press-fitted tubes. MM