Yield to Tensile Strengths Ratio Threshold Values for Ductile Materials

[struclearner]

If we need to categorize the ductile and brittle materials based upon the ratio of yield to ultimate tensile strengths of the materials.
What is the threshold values for the ratio, where the materials could be specified as ductile or brittle?

Thanks for the input.

 

[dik]

I don't know if there is a defined ratio... I consider a material as being ductile if it 'plateaus' at the yield value and is able to sustain that load for an elongation of about 20% minimum or it has to sustain a load for an amount past the point that yield is considered. There may be a more scientific definition, but I'm not aware of it. There has to be a relatively defined yield value.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

Define 'brittle'

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[weldstan]

Brittle materials are more defined by absorbed energy in an impact test at a defined operating or design temperature rather thab a tensile test performed at room temperature but that is defined by the material itself. Are you more interested in low carbon and low alloy steels?

 

No

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[EdStainless]

The mode of loading and strain rate are both factors.
If you can measure a tensile elongation in a normal tensile test then the material has ductility, even if it is only a few percent elongation.
Whack it in an impact test, is there a shear zone, any lateral expansion?
Often the combination of temperature and strain rate are more important.
And what material are you talking about? A steel with a DBT or an austenitic alloy that does not have one?
And how important is fatigue and damage tolerance?
This is a much broader issue.

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P.E. Metallurgy, consulting work welcomed

 

OK, I'll stop hinting and spell it out: there is no brittle; there are only degrees of ductility*.

* Not to be confused with impact resistance**

** Not to be confused with fracture toughness

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[struclearner]

'Ductility is usually expressed as a percent elongation in a 2-in gage length.
A ductile material has a value greater than 5% and a brittle material less than 5%."

Reference
Machine Design
Theory and Practice
Aaron D. Deutschman
Walter J. Michels
Charles E. Wilson

 

Suggest you obtain a second opinion.
And no I am not being pedantic.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."