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RE:Charpy Impact Test

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>If you design a bridge and have a normal steel with Charpy V-notch value
>of say 15 ft-lb at test temperature of 32 degree F, this steel is
>considered proper for zone 2 area where the minimum operating
>temperature is about -1 to -30 degree F.
Taken at face value this allowance is nutty. 15 ft-lb is a generally 
recognized nil-ductility transition, based on service experience with 
welded Liberty ships during World War II and an enormous amount of 
additional testing in all kinds of structures. What you're saying is that 
AASHTO allows use of welded steel structures in temperature ranges known 
to cause embrittlement, and well below the temperature range where the 
material has the ability to stop a running crack. 

There has to be something more to this. I could test a seriously brittle 
material in the upper shelf range and if I got 15 ft-lb as the impact 
energy, that would allow me to use the material at a temperature below 
the nil ductility transition where the Cv impact energy would be far less 
than 15 ft-lb. This just doesn't seem right. Perhaps AASHTO only permits 
materials with a low NDT to begin with.

Basing this requirement on the structural loading rate rather than on 
strain rates associated with running cracks also seems imprudent because 
it removes any sort of crack arrest capability from the structure. 

> Do this steel have the required
>toughness to use in area where the minimum temperature is 70 degree?
If you're talking about SA-53, I think it does in the gauges normally 
associated with pipe, based on UCS-66.

I think we're getting pretty far removed from the original question which 
deals with whether or not impact test results at 70F can be extrapolated 
to provide the Cv energy at 32F. That answer there is, 'No way...'

>The Nil Ductility temperature (NDT) of these
>metals and the exemption clause in UCS-66 may not be applicable for A53.
A-285 and A-515 are all covered by curves A or B on Figure UCS-66. A-53 
is covered by curve B.


Christopher Wright P.E.    |"They couldn't hit an elephant from
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