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thermal props of HT steel

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A quick flip thru MIL-HDBK-5A

yielded thermal expansion for:

low carbon  1025           6.78 (68F to 212F); 7.00 (68F  to 392F)
alloy steel 4130/4340     6.3   (0F to 200F)The units are 10E-06
in/in/F.   The length of the assembly would determine the absolute
differential growth.   Since the CoTE is smaller for the alloy steel
heating would actually increase the bolt prestress.  If the assembly or
rod length was about 10" the differential growth would be about .0007"
or an increase of about 2000 psi in the bolt.

 Robert Kazanjy, PE  **Disclaimer: I speak for myself not UC-Irvine**
 Senior Development Engineer
 Civil & Environmental Engineering
 UC Irvine
 E4130 EG,  Zot: 2175
 rkazanjy(--nospam--at)uci.edu


> Dave Meney wrote:

> <SNIP>
> Does anyone know whether the thermal coefficient of expansion for a
> high
> tensile bolt (UTS=1050 MPa, yield stress = 945 MPa) is any different
> to that
> for mild steel?
>
> I have a problem where an argument has been raised regarding the loss
> of
> pre-tension in a torqued screw, where the screw is high tensile and
> the
> components are mild steel.  The claim is that after heating the
> assembly to
> 130°C (266°F) for a couple of hours, the thermal differences in the
> two
> steels causes significant loss of prestress.
>
> Any comments?
>
> Thanks,
> Dave Meney
> Structural Engineer