Autofrettage

The autofrettage technique is discussed by Manning (1950) and Jawad and Farr (1989). 

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Autoclave tape Autodoping AUTOFLEX Autofrettage Autogenousmilling Autograft... 

In practice a uniform distribution of the working stress cannot be achieved, but it may be approached by various methods of constmction such as compound shrinkage, tape winding, and autofrettage which have their origin in the design of ordnance. 

Eig. 7. Pressure expansion curve of a thick-walled cylinder undergoing autofrettage (22). 

Autofrettage of small bore tubes can be effected by pushing highly poHshed and generously lubricated oversized drifts or balls through the bore. 

Fig. 18. Repeated pressure tests on autofrettaged EN25 steel cylinders, k = 2.25, with cross-bores (86,96). A, Autofrettaged at 324 MPa ...

Relaxation of the residual stresses induced by autofrettage at 720 MPa (104,400 psi) in reactor tubes k = 2.4), of AISI 4333 M6 at a uniform temperature of 300°C has been studied and it was concluded, on the basis of creep tests for 10,000 h, that after 5.7 years 60% of the original stress would remain (161). 

A. E. Macrae, Overstrain of Metals and its Application to the Autofrettage Process of Cylinder and Gun Construction, HMSO, London, 1930. 

The overspeed test is a form of proof test, in that it looks for a failure. In this case, it is a permanent deformation. Not all permanent deformations are failures. In fact, manufacturers have autofrettaged high tip speed impellers for decades. The fourth edition of API 617 was somewhat misleading as it identified the bore as the only critical area. On... 

Autofrettage in Fr Kaltrecken in Ger Samoskrepleniye Stvola, in Rus), Autofrettage is a process for manufg gun barrels, in which the inner surface layers of a plain... 

Autofrettage is also used for strengthening the walls of tubes, cylinders, pressure vessels, etc and it is claimed that it nearly doubles the elastic strength of the walls... 

Potential (pressure) fluid energy up to 10000 up to 5000 up to 4000 autofrettage (residual stresses) hydroforming isostatic pressing (sintered parts)... 

The autofrettage treatment (Fig. 1.4-9, B) is certainly one of the oldest, but still very useful methods to create beneficial residual stresses in thick-walled components (e.g., pipes). The autofrettage pressure must be adjusted to a level so that the material in the thick wall is plastically strained within a certain percentage (e.g., 50 %), the rest staying only elastically strained. 

Figure 1.4-10. Stresses in an autofrettaged thick-walled cylinder (plastification 50% through the wall)...

CT = tangential stress without autofrettage OtA = tangential stress with autofrettage 0m -tangential residual stress after autofrettage... 

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