Tresca, Von Mises and Luder bands 2

[Hurricanes]

I recently managed to get hold of a copy of 'Design of Piping Systems' by the M W Kellogg company. In the chapter relating to strength of materials, it discusses yield conditions, detailing both the Tresca and the von Mises yield conditions.

Where it got interesting for me was the discussion of low carbon steels which typically have an upper and a lower yield point. As the limit stress is based on the lower yield point, it is the stress required for the Luders bands to widen.

Only the shear stress acting in the plane of the Luders bands can cause them to widen, and as the intermediate principal stress is perpendicular to the bands it must be ineffective. Therefore the yield condition is closer to Tresca than von Mises.

Is this why the ASME codes use Tresca rather than von Mises? My other piping books make no mention of Luders bands, one says Tresca is preferred as it is mathematically simpler compared with von Mises.

Does anyone know of any references which discuss this further?

I have read through previous discussions here on Tresca, Von Mises and Principal stresses, but this doesn't seem to have been mentioned.

 

[BigInch]

I don't know, but if I had to guess, it would be because Tresca is the simplest one.

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"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[JohnBreen]

Yet another gold star for BigInch!

The ASME B31 Committee chose the Tresca criteria simply because it is the easiest to calculate - no technical issue involved. The ASME B31 Codes strive to present a simplified methodology for design and analysis of piping systems.

Glad to see that you are reading the Kellogg book - you might also find this one interesting from a historic perspective:

http://www.scribd.com/doc/15454461/Spielvogel-Piping-Stress-Calculatons-Simplified

Just remember that the above book was written before we changed the allowable stress to 2/3 yield and some of what is in the book is obsolete.

Some other interesting reading on this topic:

http://www.scribd.com/doc/20061898/Chapter-b04-stress-Analysis-of-Piping-System

Regards, John

 

[Hurricanes]

Thanks to both of you for clearing that up.

Thanks for the texts, John. Spielvogel's book should make for some interesting bedtime reading.