I intend to manufacture a high pressure cylinder in the size of below
inner diameter : 29 mm outer diameter : 77 mm length : 286 mm
This cylinder will be mounted on a high pressure waterjet pump and the cyclic working pressure is about 4000 bar. I manufactured a cylinder and mounted it on the waterjet pump but it crashed in a few days.
To extend this cylinder's service life this cylinder must be autofrettaged, but i do not know how i can do this...
As far as i know, autofrettage is a process that inside of the cylinder pressurized up to 10.000 bar and then pressure released than this cylinder is autofrettaged, inside of the cylinder has a plastic deformation and the outer of the cylinder is under elastic deformation that causes always preloading stress through the center of the cylinder.
Are there anybody who know more about autofrettage? How can i achive this process?
Please email me at my snipped-for-privacy@yahoo.com
Autofrettaging is a way of strengthening gun barrels and thick cylinders by applying a sufficiently high pressure, called plasticizing pressure so that the inner half or two-thirds goes into plastic condition, but returns to elastic condition and then is compressed by grip of outer layers while autofrettaging pressure is
slowly released. It is also called pre-stressing. An easy way driving in oversized inner cylinder to have an effect of heated shrink fit in steel cylinder situation.
It is dealt with as an Advanced Strength of Materials subject in post graduate classes.Thin shell formulas indicated in earlier post here won't do. At thick shell inner radius, fiber stresses peak up 2 to 3 times compared to the thin shell circumferential values.
There are 3 options:
1) Single thick cylinder layer only: Calculate plasticizing pressure,and benefit over the thick cylinder values. Also check whether such facility is available.
2)Two sleeves shrink/interference fit.Calculate for the interference amount in mm needed from the elastic properties and dimensions of the two parts.
3)Choice of composite fiber / filament overwrap and a thin liner.
Text book 'Advanced Strength of Materials' by Den Hartog outlines the process and design methods is good for a start. But it is best to depend on expertise in some training and participatory mode.The first design document is valuable.
Stainless steel and carbon fiber overwrap combination is easily implementable for the small size you have in mind, but is another ew line of technology. By a careful calculation procedure that accounts for all properties of liner and composite overwrap one has to keep fiber and liner stresses in limits and avoid liner buckling when autofrettaging pressure is released.
In Aerospace applications one uses Kevlar and Carbon fibers impregnated with epoxy resin and cured to go to high stresses by Filament Winding process after winding on cylinder at certain helix angles.
Aluminum alloys can be used to be pessure contributory as liners, a special design process prevents buckling. It reduces pressure vessel weight for space application.
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