Notched specimen and brittleness

[Gunde]

How would you explain the fact that a notched specimen* of a ductile metal becomes brittle when tested uniaxially?

The notch produces three axial tensions. But why does three axial tension cause brittleness?

And how does the tension distribution look like in the notched area?

Thanks!


*(Round pole, with a radius, aluminium)

 

[PerennialII]

Hi Gunde,
what you're talking about is the effect of stress triaxiality on failure strain (or toughness/ductility overall) in metallic materials. It is a common response in metallic materials to notches and cracks, and in general as said, a sensitivity of toughness to the nature of the prevailing stress fields.

The micromechanical explanation is related to the how stress triaxiality affects the mechanisms of ductile tearing ... it is a factor in void nucleation, growth and coalesence (growth of voids in particular), thereby resulting in decrease of ductility related material properties.

Example of modeling of the phenomenon and some related experimental work (a pretty good review actually) is given for example in the PhD thesis below:
http://www.mt.mek.dtu.dk/reports/PHDthesis/pdf/rt.pdf

... + there are several review articles available which can point out if you're interested, still an area of intense study (think can dig you for example some finite element results to display the different effects if you're interested).

 

[Gunde]

Thanks!

It’s all coming together now.

If you can find some finite element results and point out a few articles that would be great.

 

[PerennialII]

Sure thing, I'll PM you the address of a package I'll upload to a hosting service.