The autofrettage process is widely used in various industries for increasing operating pressures for advanced industrial, automotive, aerospace and defense . The detailed numerical comparison between the two different autofrettage processes points to the fact that the swage autofrettage process is. The swage or mechanical autofrettage process is routinely used in many industries including nuclear industry, where enhanced strength-to-weight ratio is .
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The end result is an inner surface of the gun barrel with a residual compressive stress able to counterbalance the tensile stress that autofrdttage be induced when the gun is discharged. In addition the material has a higher tensile stress as a result of the heat treatment process.
In modern practice, a slightly oversized die is pushed slowly through the barrel by a hydraulically driven ram. 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 goal of autofrettage is to increase the durability of the final product.
Autofrettage – Wikipedia
Autofrettzge technique has been applied to the expansion of tubular components down hole in oil and gas wells. 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.
A residual compressive stress remains on the barrel’s inner surface, even after final honing and rifling. Retrieved from ” https: While autofrettage will induce some work hardeningthat prlcess not the primary mechanism of strengthening.
The strain is proportional to the stress applied within the elastic limit; therefore the expansion at the outer layers is less than at the bore.
This article needs additional citations for verification. The tube is subjected to internal pressure of sufficient magnitude to enlarge the bore and in the process the inner layers of the metal are stretched in tension beyond their elastic limit.
Its maximum value occurs in the metal adjacent to the source of pressure, decreasing markedly towards the outer layers of the tube.
Articles needing additional references from June All articles needing additional references. Inducing residual compressive stresses into materials can also increase their resistance to stress corrosion cracking ; autofrettagd is, non-mechanically-assisted cracking that occurs when a material is placed in a corrosive environment in the presence of tensile stress. Because the outer layers remain elastic they attempt to return to their original shape; however, they are prevented from doing autofrettzge completely by the new permanently stretched inner layers.
Archived from the original PDF on Please help improve this article by adding citations to reliable sources. The reason why this is possible is that the stress distribution through the walls of the tube is non-uniform. The start point is a single steel tube of internal diameter slightly less than the desired calibre.
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. Views Read Edit View history. 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.
The term zutofrettage 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.
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 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.
The effect is that the inner layers of the metal autofdettage put under compression by the outer layers in much the same way as though an outer layer of metal had been shrunk on as with a built-up gun. In early practice of autofrettage of a gun barrel, the barrel was pressurized hydraulically.
From Wikipedia, the free encyclopedia.