What is the difference of DBTT & FATT 1

[Jason8zhu]

Dear all,

It seems that both DBTT & FATT are reflecting the temperature from ductile to brittle.
Any difference between DBTT and FATT:
-ductile-brittle transition temperature (DBTT)
-fracture appearance transition temperature（FATT）


Thanks.

 

[metengr]

Yes, there is a difference, the FATT is the fracture appearance transition temperature where the FATT value is based on the change from cleavage to shear fracture appearance percentage for a broken CVN impact specimen. Commonly, FATT₅₀ is used, where 50 refers to 50% cleavage and 50% shear fracture appearance on a broken CVN impact specimen.

The DBTT is similar except the DBTT value is based on the inflection point of a CVN impact energy versus test temperature curve, where the CVN upper shelf (ductile) changes to lower shelf CVN (brittle) values at a specific test temperature.

 

[EdStainless]

Both of them are constructs that help us define changes in behavior. In some materials they are very similar, in some they are very different.
You can do similar things with K1c and other fracture or fatigue tests. People tend to use impact because it is fast, cheep, and easy. But remember in either case the mathematically determined 50% point is already well into the brittle region, you to ask what level of property degradation the application can tolerate.

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P.E. Metallurgy, Plymouth Tube

 

[Jason8zhu]

Thanks metengr & EdStainless for your kindly interpretation.