SAME MATERIAL WITH DIFFERENT ALLOWABLE STRESS 4

[LP2111]

WHAT TO SELECT WHEN THERE ARE DIFFERENT VALUES FOR ALLOWABLE STRESS FOR THE SA-307 B(BOLTING) MATERIAL?

 

[Gr8blu]

See previous (ancient) thread covering this topic.

https://www.eng-tips.com/viewthread.cfm?qid=188143

Converting energy to motion for more than half a century

 

[LP2111]

I THINK I AM NOT ABLE TO EXPLAIN MY QUESTION. FOR EXAMPLE TAKE SA-193 MATERIAL. NOW LINE NO. 28 & 31 HAVE SAME MATERIAL LISTED BUT HAVING DIFFERENT ALLOWABLE STRESS VALUE. WHY?
WHAT IS THE `t' SHOWN IN LAST COLUMN? IF I HAVE TO CHOOSE BETWEEN THEM.. THEN WHAT CRITERIA SHALL BE FOLLOWED?

 

[XL83NL]

It’s the thickness or dia of the bolt. Thicker usually means lower allowables above some point. What else is there to explain? Did that answer your question?

Huub
- You never get what you expect, you only get what you inspect.

 

[LP2111]

thank you for your valuable responses!!

 

[Christine74]

While we're here, can anyone here explain why the allowable stress of some bolting materials drops as the diameter increases? Does the manufacturing process result in the outer portion of the bolt having a higher tensile strength than the inner portion?


-Christine

 

[EdStainless]

C74, Often yes.
When you roll threads the cold work diminishes with depth.
The result is that with smaller diameters you get significant cold work while with larger ones a greater portion of the interior is not cold worked.
You also see a similar result (though from a different cause) with heat treated fasteners.

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P.E. Metallurgy, consulting work welcomed

 

[Christine74]

Makes sense, thanks for explaining that EdStainless.


-Christine

 

[Pengar]

Christine 74,
The steels tensile and yield strength, thus the allowable stresses, drops when diameter increases due to fabrication process. When the thickness increases the material cooling slows and the grain structure is larger. If the material is thin, the cooling of the material during fabrication is quicker and the grain structure is smaller. Also, when the material is cold formed, the fabrication process increases the yield stress and the allowable strenght.