The question is not precise enough to exactly know what you mean, but here are some inputs. The ductile-to-brittle transition temperature is thermally dependent, but since strain rate has a similar yet inverse effect on dislocation movement, it is also affected by strain rate (but not significant in most applications). Any embrittling factors will also affect the ductile-to-brittle transition temperature. Hope this is of any help to you!

https://www.researchgate.net/publication/229038999_An_empirical_correlation_between_temperature_and_activation_energy_for_brittle-to-ductile_transitions_in_single-phase_materials

Article An empirical correlation between temperature and activation ...

Dear Jimmy,

the ductile brittle transition of materials has both thermal as well as athermal component.

The thermal part is related to the dislocation movements i.e flow of material and athermal is on the stochastic behavior of cleavage triggers ahead of crack front.

Any sample in transition region shows a full transition along the crack surface if you see the fracture surface, unless the test is done at lower shelf. Initial area of crack front will show dimples and later cleavage facets. The transition also varies with amount of constrain loss, more loss of constraint will decrease the transition region towards lower temperature.

You may have a look at http://www.sciencedirect.com/science/article/pii/S0013794415002386 for more details.

With regards,

Abhishek

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