Wrinkled/textured metal surface after test. 3

[acspain]

Hello all,

Upon testing some electro-polished metal test specimens, axially and in tension, the smooth electro-polished surface changes dramatically to a wrinkled or textured surface, why?

I can't seem to find anything that explains this effect on the internet, including academic papers and these forums. It is likely that I don't know the correct terminology. My guess at this point is that the change is due to the grains deforming/twisting/slipping and thus disrupting the originally smooth surface. References to papers or other resources to help explain this effect is most welcome.

The parts are small, roughly 0.2 mm square cross section and are cut from tubing with a 3 mm outer diameter. The material is 316 stainless steel with a grain size print call out of > or = to 8 per ASTM E112.

A picture is attached to illustrate. The tab (on the left) shows the original surface while the small area (on the right) shows the deformed surface.

Thank you for any help you can provide.
acspain

 

[FennLane]

It is well known that the free surfaces of metals become rougher during plastic
deformation. Many studies show the influence of strain, grain size, stress
mode and texture on surface roughness characteristics.
The surface roughness is found to increase linearly with
strain and depends linearly on grain size The
roughness increment is not very dependant onthe stress state
whereas texture has been found to have a great influence on
the roughness.7–9 Most of these studies are aimed at
A number of studies have shown that
plastic deformation roughens a surface by introducing
slip bands within grains and strain incompatibilities
between grains.

O. Wouters, W. P. Vellinga, R. van Tijum and J. T. M. de Hosson:
Acta Mater., 2005, 53, 4043–4050.
M. R. Stoudt and R. E. Ricker: Metall. Trans. A, 2002, 33A, 2883–
2889.
Y. Z. Dai and F. P. Chiang: J. Eng. Mater. Technol. Trans. ASME,
1992, 114, 432–438.
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Int., 2003, 43, (11), 1795–1798.
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1998, 80–81, 707–712.
Y. Z. Dai and F. P. Chiang: Mech. Mater., 1992, 13, 55–57.
O. Wouters, W. P. Vellinga, R. van Tijum and J. T. M. de Hosson:
Acta Mater., 2006, 54, 2813–2821.
Y. S. Choi, H. R. Piehler and A. D. Rollett: Metall. Trans. A, 2004,
35A, 513–524.
R. Becker: Acta Mater., 1998, 46, (4), 1385–1401.
I. Shimizu, T. Okuda, T. Abe and H. Tani: JSME Int. J. Ser. A,
2001, 44A, (4), 499–506.

 

[EdStainless]

Luder's lines

http://www.advantagefabricatedmetals.com/metalformingglossaryl.html

from the non uniform straining of the surface.

Or Orange peal, that has to do with dislocation slip in coarse grained structures.

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