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Non uniform cross section heads similar to ASME VIII App.1 1.6

Non uniform cross section heads similar to ASME VIII App.1 1.6

Non uniform cross section heads similar to ASME VIII App.1 1.6

(OP)
I have a head-banger.

A small head, so small it's more economic to machine than forge, that is similar to ASME VIII App.1 Fig 1.6 except that:

1. The internal cavity is spherical;
2. The external face is flat, flush with the top of the
   flange ring.

Here's the problem:

1. Where does the reaction between head and falnge ring
   occur? i.e. How do I deteremine the radial moment?
2. Is the fact that (effective) 'radial-thickness' varies
   such that it is indeterminate if the problem is
   plane-stress or plane-strain an issue?

I think the answer to 2. is yes, because it may produce additional loadings and hence additional moments for the flange ring and the bolting.

Any ideas? Any good links?

Take note, FEA proves the equations in 1.6 to be inadequate for this form.

Some body give me an answer, the curlings finished, Britian won, Olympics over, no execuses.

Regards,

Fawkes.

RE: Non uniform cross section heads similar to ASME VIII App.1 1.6

(OP)
Can I just add one point of clarification to what I've said above. When I stated that 1.6 is inadequate, what I mean is that the FEA shows there to be an excessive factor of safety. The reults show the construction to be extremely conservative and hence uncompetitive.

RE: Non uniform cross section heads similar to ASME VIII App.1 1.6

I'm not sure I fully understood your geometry.
Anyway if you need to comply with the code, the only thing you can do is to 'carve' your actual shape till you obtain a geometry that suits one of those in Fig.1.6.
Of course this procedure will give a very safe result.


prex
motori@xcalcsREMOVE.com
http://www.xcalcs.com
Online tools for structural design

RE: Non uniform cross section heads similar to ASME VIII App.1 1.6

(OP)
The geometry:

Right, think of the sillouette of an arched bridge, flat top, flat sides, with an arch cut out of the base, this is similar to the cross section I'm looking at.

The form is already set 'similar' to Fig 1.6, what I'm after is reducing the machining time without considering such high factors of safety.

Don't get me wrong, if high SOF is required then that is the design parameter, however, everybody's looking to be more competitive.

It's just, if engineers look to improve competition it's done safely, if accountants do it; well!!

Fawkes

RE: Non uniform cross section heads similar to ASME VIII App.1 1.6

You didn't specify if you need to comply with the code.
If you do not, then you are free to use any method for dimensioning, perhaps FEA, as you mentioned it.
Otherwise I think you should use fig.1-6(d), take t as the thickess left at the apex of your dome, L as the internal radius of sphere, B where the internal sphere intersects the face of the flange, and hr wherever the mid-thickness line will meet the B diameter.
Of course if your dome is a full emisphere or near to that, this procedure could give an odd and really excessively safe result, but once again: if you need to comply with the code...
Another thought: a flanged dome with a flange thickness equal to the dome height is also quite odd. Perhaps your flange thickness is already in excess, but of course as you machine it, you don't want a thinner flange.
Why don't you just use a flat head?


prex
motori@xcalcsREMOVE.com
http://www.xcalcs.com
Online tools for structural design

RE: Non uniform cross section heads similar to ASME VIII App.1 1.6

Since you are looking at a design that has a lot more material than an optimum shape, is it possible to eliminate the hemispherical cavity all together, and have a blind flange?

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