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Duzshura Although the outer layers of the tube are also stretched, the degree of internal pressure applied during the process is such that they are not stretched beyond their elastic limit. The effect is that the inner layers of the metal ahtofrettage put under compression by the outer proess in much the same way as though an outer layer of metal had been shrunk on as with a built-up gun.

This means that the inner layers have been stretched to a point where the steel is no longer able to return to its original shape once the internal pressure has been removed. Autofrettage is a metal fabrication technique in which a pressure vessel is subjected to enormous pressurecausing internal portions of the part to yield plastically, resulting in internal compressive residual stresses once the pressure is released.

The end result is an inner surface of the gun barrel with a residual compressive stress able to counterbalance the tensile stress that would be induced when the gun is discharged. The tube is subjected to internal pressure of autifrettage magnitude to enlarge the bore and in the process the inner layers of the metal are stretched in tension beyond their elastic limit.

The term autofrettage is also used to describe a step in manufacturing of composite overwrapped pressure vessel COPV where the liner is expanded by plastic deformationinside the composite overwrap. By using this site, you agree to the Terms of Auyofrettage and Privacy Policy. Inducing residual compressive stresses into materials can also increase their resistance to stress corrosion cracking ; that is, non-mechanically-assisted cracking that occurs when a material is placed in a corrosive environment in the presence of tensile stress.

June ;rocess how and when to remove this template message. Because the outer layers remain elastic they attempt to return to their original shape; however, they are prevented from doing so completely by the new permanently stretched inner layers.

Archived from the original PDF on Its maximum value occurs in the metal adjacent to the source of pressure, decreasing markedly towards the outer layers of the tube. The goal of autofrettage is to increase the durability of the final product. The amount aytofrettage initial underbore and oversize of the die are calculated to processs the material around the bore past its elastic limit into plastic deformation.

The technique is commonly used in manufacture of high-pressure pump cylinders, warship and tank gun barrels, and fuel injection systems for diesel engines. The start point is a single steel tube of internal diameter slightly less than the desired calibre. Autofrettage proceess The reason why this is possible is that the stress distribution through the walls of the tube is non-uniform. The method has been patented by the Norwegian oil service company, Meta, which uses it to connect concentric tubular components with sealing and strength properties outlined above.

In early practice of autofrettage of a gun barrel, the barrel was pressurized hydraulically. This page autofrettave last edited on 29 Octoberat The strain is proportional to the stress applied within the elastic limit; therefore the expansion at lrocess outer layers is less than at the bore. Finally, the elasticity of the barrel can be tested by applying internal pressure once more, but this time care is taken to ensure that the inner layers are not stretched beyond their new elastic limit.

This article needs additional citations for verification. While autofrettage will induce some work hardeningthat is not the primary mechanism of strengthening.

Articles needing additional references from June All articles needing additional references. Unsourced auyofrettage may be challenged and removed. In addition the material has a higher tensile stress as a result of the prcess treatment process.

Please help improve this article by adding citations to reliable sources. The next step is to subject the compressively strained inner layers to a low-temperature heat treatment which results in the elastic limit being raised to at least the autofrettage pressure employed in the first stage of the process.

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The conglomeration of these materials producing a solid mass is called plain concrete. By sim- It is easier to use. Where the contractor is responsible in establishing the mixture proportion that will achieve the required strength and workability as specified in the plan. Aside from its rapfd hardening properties, it can resist chemical attack by sulfate and weak acids including sea water.



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