Notched specimen and brittleness

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Discussion Overview

The discussion revolves around the phenomenon of brittleness in notched specimens of ductile metals when subjected to uniaxial testing. Participants explore the relationship between stress triaxiality and material properties, particularly focusing on the effects of notches on ductility and toughness.

Discussion Character

  • Technical explanation
  • Exploratory

Main Points Raised

  • One participant inquires about the mechanism by which three axial tensions from a notch lead to brittleness in ductile metals.
  • Another participant explains that stress triaxiality significantly influences failure strain and ductility in metallic materials, linking it to void nucleation and growth.
  • References to micromechanical explanations and the relationship between stress fields and toughness are introduced, suggesting ongoing research in this area.
  • Participants discuss the availability of modeling examples and experimental work related to the topic, indicating a willingness to share resources for further exploration.

Areas of Agreement / Disagreement

Participants appear to agree on the relevance of stress triaxiality to the brittleness of notched specimens, but the discussion remains exploratory without a consensus on specific mechanisms or models.

Contextual Notes

The discussion does not resolve the complexities of the tension distribution in the notched area or the specific conditions under which brittleness occurs, leaving these aspects open for further investigation.

Who May Find This Useful

This discussion may be useful for materials scientists, engineers, and researchers interested in the mechanical properties of metals, particularly in relation to stress analysis and failure mechanisms.

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

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