Disadvantages Of Autofrettage

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3. Types of autofrettage
Autofrettage introduces compressive hoop stresses in the region surrounding the internal diameter, to reduce the magnitude of the hoop stresses developed there when the tube is pressurized. This may be accomplished in one of two ways, as described in sub-sections 3.1 and 3.2.
3.1 Hydraulic Autofrettage
Hydraulic autofrettage involves the application of hydrostatic pressure to the internal diameter of the tube. The stress produced due to the hydraulic pressure should exceed the material yield stress and elastic deformation should begin. The pressure is further increased to propagate the deformation to the desired depth within the tube wall. Non-corrosive and non-compressibility of oil makes it a good fluid for the application as compared to a highly compressible gas. Overall this reduces both the work done when increasing its pressure, and danger …show more content…

[9] O’Hara, G P, “Analysis of the Swage Autofrettage Process,” US Army ARDEC Technical Report ARCCB-TR-92016, Benét Laboratories, Watervliet Arsenal, NY 12189, USA, 1992. Even with the use of lubricants a considerable amount of axial force is applied by the mandrel to the tube, a need to constraint it raises. Constraint locations include either the mandrel entry or exit ends. The location determines whether the deformed length of tube is held is tension (the former case) or the un-deformed length is compressed (the latter). Just like the Open- and Closed-Ends cases of hydraulic autofrettage, these axial stresses effect the precision of the radial stress patterns developed. The tube modelled by O’Hara [9] was constrained at its mandrel entry end, around its OD. [9] O’Hara, G P, “Analysis of the Swage Autofrettage Process,” US Army ARDEC Technical Report ARCCB-TR-92016, Benét Laboratories, Watervliet Arsenal, NY 12189, USA,

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