Converting hardness to fracture toughness 2

[MightyJ]

Does anyone have the equation to convert hardness (vickers) to fracture toughness? I would think it's only for certain materials but, could be a useful equation for me to have. I will continue to look for it and will post it if I find it. Thanks

 

[metengr]

There is no such equation for converting hardness to fracture toughness.

 

[Wrenchbender]

Agreed. There is no quantitative relationship between frax toughness and hardness/tensile strength. If you still need a rough guide read 'Rapid and Inexpensive Tests for Determining Fracture Toughness' report 328, 1976 by the National Material Advisory Board, and look at Figure 1.

http://books.google.com/books?id=NG...esult&ct=result&resnum=1#v=onepage&q=&f=false

 

[MightyJ]

Ah, yes you guys are right there is no exact conversion or relation, though maybe I ment there was a way to obtain a fracture toughness reading when doing a hardness test. I just found the calculations and attached them in pdf. It is based on using a macro vickers indent and measuring the cracks emanating from each corner. Obvious, but still useful and neat.

 

[CoryPad]

Fracture toughness calculated from crack length during indentation testing is going to be limited to brittle materials. Is this for a metal? This technique is more suited to ceramics, where it has been developed more thoroughly.

 

[metengr]

CoryPad;
The above software is apparently used on intermetallic compounds as one of several methods as indicated below

http://www.sciencedirect.com/scienc...serid=10&md5=8c04d97f3ffdf9bbfa13014911259240

I don't see any application to typical metals or alloys. Amazing what a little internet leg work can do.

 

[CoryPad]

I had past experience with this for ceramics; brittle intermetallic compounds would be an obvious extension. The technique really isn't suited toward metals, so this topic would be better if placed in Forum367.

 

[MightyJ]

Yes, only for brittle materials (so mostly ceramics). It's obvious you need to have crack propagation to even do the calculation. It could be moved, and might be very useful to someone. I have heard the KIC SHETTY is the most commonly used also.