Calculating stress in metallic cable prior to setting

Calculating stress in metallic cable prior to setting
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Posted by: Bender ^®

05/01/2006, 13:27:21

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Hi All,

I've got a situation where I'm trying to calculate the minimum stress it will take to induce set in a mineral-insulated cable being wound arond a spool.

For those of you not familiar with them, mineral-insulated cable is a metal sheath with a 90% compacted powder ceramic packing and metallic core wire. In this particular case, I've got a .125 OD cable, Inconel 600 sheath, ~.015 to .020 wall with a .020" core wire. The ceramic insulation makiing up the annulus is very tightly compacted but since each grain is quite small (think icing sugar) the cable tends to be somewhat flexible. For simplicity I am analyzing the cable as a solid rod/wire of Inconel.

I have a customer asking what is the minimum spool diameter to use where the cable can be paid-off and retracted numerous times without the sheath setting. We've never had this request before so we don't have any data to compare this request with. I've used the basic elastic bending eqn sigma=Mc/I in conjection with the radius of curvature eqn, rho=EI/M. I'm not getting a solution which makes sense. I would appreciate any input on this. Thanks.

Modified by Bender at Mon, May 01, 2006, 13:44:08

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