Talk:Rheid

Should include a mention of glass, a common rheid that most people are familar with. Many have seen historic colonial homes where the glass at the bottom of the pane is noticeably thicker than the top. R Stillwater (talk) 00:24, 8 November 2008 (UTC)

Wrong. This is a myth that should not be perpetuated here. Glasses made before the development of modern float processes were non-uniform in thickness; many historic panes are noticeably thicker at one end or the other--according to MIT's Egon Orowan (1902-1989), half are thicker at the top.

Any rational consideration of the matter should be sufficient to dismiss such persistent nonsense.

One also wonders why this alleged thickening is confined to the glass in...windows. Why don't we find that Egyptian cored vessels or Hellenistic and Roman bowls have sagged and become misshapen after lying for centuries in tombs or in the ground? Those glasses are 1,000–2,500 years older than the cathedral windows....

It is worth noting, too, that at room temperature the viscosity of metallic lead has been estimated to be about 10 to the 11th power, (10¹¹) poises, that is, perhaps a billion times less viscous—or a billion times more fluid, if you prefer—than glass. Presumably, then, the lead caming that holds stained glass pieces in place should have flowed a billion times more readily than the glass. While lead caming often bends and buckles under the enormous architectural stresses imposed on it, one never hears that the lead has flowed like a liquid.

The above-cited information is the work of Robert Brill, who has published peer-reviewed studies as the chairman of the Committee on Archeometry of Glass, a technical committee of the International Commission on Glass (ICG) established for the scientific study and -conservation of historical glass. In 1990, he received The Pomerance Award for Scientific Contributions to Archaeology from the Archaeological Institute of America.

Patronanejo (talk) 02:14, 23 November 2012 (UTC)

Definition

The original introduction as expressed on 01 April 2005 by the originator of this article, GeoGreg, defined Rheid as follows:

In geology, a rheid is a solid material that deforms by viscous flow. To be considered a rheid, deformation by flow should exceed elastic deformation by at least a factor of three.

This was revised on 2 December 2010 by Marie Poise to:

In geology, a rheid is a solid material that deforms by viscous flow.

Marie Poise emended her heavily truncated result by moving the "See also" links into the introductory text, creating the current definition:

In geology, a rheid /ˈriːɪd/ is a solid material that deforms by viscous flow. The term has the same Greek root as rheology, the science of viscoelasticity and nonlinear flow.

There is much in the current passage that is recognisable from the original as contributed by GeoGreg.

Unfortunately, it is also recognisable from the McGraw-Hill Dictionary of Scientific & Technical Terms (Sixth Edition), 2003 .

A substance (below its melting point) which deforms by viscous flow during applied stress at an order of magnitude at least three times that of elastic deformation under similar circumstances.

I am not a geologist, so I am not sure if there is any significant difference in the way I've worded the following three options:

If at temperatures below its melting point a solid experiences crystalline reorganization in response to regions of compressive force--shifting its constituent molecules or atoms such that mass appears to be transferred (or "flow") to domains under lesser compressive force--that solid may be considered to be a rheid.

A rheid /ˈriːɪd/ is a solid which experiences crystalline reorganization in response to domains under atypical compressive forces, shifting its constituent atoms or molecules such that mass appears to be transferred (or "flow") to regions under lesser pressure.

A rheid /ˈriːɪd/ is a solid which undergoes crystalline reorganization at temperatures below its melting point, shifting its constituent atoms or molecules in response to domains experiencing atypical compressive forces such that mass appears to be transferred (or "flow") to domains under lesser pressure.

I am going to select one and replace the current passage; please revert if the result conflicts with geological reality. --Patronanejo (talk) 09:20, 23 November 2012 (UTC)

EDIT Here's what I ultimately decided on:

A rheid /ˈriːɪd/ is a non-molten solid which experiences crystalline reorganization in response to domains under atypical compressive forces, shifting its constituent atoms or molecules such that mass is convected to regions under lesser pressure. --Patronanejo (talk) 10:09, 23 November 2012 (UTC)

Hi Patronanejo, thanks for having a go at this, but I don't find any of your proposed definitions effective at describing what a rheid is. I've gone back to using something based on Carey's original definition as described by Arthur Holmes. It's bound to bear some relationship to the form of words used in the McGraw-Hill dictionary - note that Neuendorf uses "A substance (below its melting point) that deforms by viscous flow during the time of applied stress at an order of magnitude three times that of the elastic deformation under similar conditions"[1] without attribution - there aren't too many ways of describing this, while still honouring the original. Unfortunately I don't have access to the original Carey paper, so I can't be sure exactly how he put it. Mikenorton (talk) 22:05, 23 November 2012 (UTC)

Hi Mikenorton, I have a feeling you're right--inevitably, ESGLO also uses the same definition. I described what I understand to be our best model for the non-molten migration of highly-compressed solids at a molecular level.

S. Warren Carey's paper on rheidity was published in the very first Journal of the Geological Society of Australia (1953, link to abstract only). He defines it as follows:

The rheidity of a substance is defined as that property which determines whether it will behave as a fluid or solid for a particular experiment. It may be measured for given conditions of temperature, pressure, and shear stress, by that time for which the shear must be maintained for the deformation by viscous flow to exceed by one thousand times the elastic deformation. When loads are maintained for longer than the rheidity, the substance deforms as a fluid, and the elastic terms of the deformation equation may be neglected as insignificant.

It's not a definition that seems to make any attempt to describe the phenomenon at a fundamental level--but as my training is in molecular biology, there is no way I am going to dispute anyone's understanding of geophysics (particularly the temporal dimension of rheidity, but I'm also less-than-comfortable with the rheology of non-Newtonian fluids)

--Patronanejo (talk) 15:56, 2 December 2012 (UTC)

Thanks for the link - I think that I've honoured that reasonably well, but maybe someone will be along to correct that view. non-Newtonian fluids are indeed strange beasts. Rock salt moves as a Newtonian fluid when buried beneath younger deposits over a geological timescale, as a non-Newtonian fluid at the earth's surface as in a salt glacier in the wet season on a timescale of days and weeks or you can break it into pieces with a hammer on a much shorter timescale. Mikenorton (talk) 16:11, 2 December 2012 (UTC)

Thank you for the historical perspective. No doubt you detected in my edits an unarticulated suspicion that viscosity--as a Newtonian concept--is not entirely adequate as the basis of a useful description of rheidity. Presented with Carey and Neuendorf for context, I am come to understand that any alternative needs be legitimised by no small claim to authority in geophysical- or non-Newtonian continuum mechanics.

It was much easier to propose an alternative under the impression that the original editor was a less-than-selective plagiarist!

Thank you also for briefly addressing the temporal dimension of the rheidity of salt deposits. My understanding of the temporal aspect has been almost-entirely derived from Marcus Reiner's 1963 comments to the Fourth International Conference on Rheology in Providence, Rhode Island.

Reiner, Marcus (August 1963). "The Deborah Number" (PDF). Physics Today, January 1964. 17 (1): 62. doi:10.1063/1.3051374. Retrieved 10 February 2007.

--Patronanejo (talk) 04:45, 3 December 2012 (UTC)