- #1
foolosophy
- 35
- 0
Is Yield Stress for a fluid a real property?
Or is it a time dependent illusion we are measuring?
For example - some glass materials are referred to as super-cooled fluids and yet behave and appear like solids. In reality though these super cooled fluids flow - very slowly.
Some old glass windows on churches etc, are thicker at the bottom than the top.
One of the oldest continuous experiments is still been monitored in Australia- "The Pitch Drop Experiment"
This experiment involves the filling of a glass funnel with a very viscous pitch material. The experiment shows that the pitch flows very slowly through the opening - about one drop per decade. Its been running sonce the early 1930's and still going.
If you strike this material with a hammer it shatters into pieces like a block of glass.
So what is yield stress? Techincally its the stress that must be overcome in order for a fluid to begin shearing or flowing. But what if it takes decades for the flow to be measured? An apparentlt sold material is flowing!
Weird stuff
Or is it a time dependent illusion we are measuring?
For example - some glass materials are referred to as super-cooled fluids and yet behave and appear like solids. In reality though these super cooled fluids flow - very slowly.
Some old glass windows on churches etc, are thicker at the bottom than the top.
One of the oldest continuous experiments is still been monitored in Australia- "The Pitch Drop Experiment"
This experiment involves the filling of a glass funnel with a very viscous pitch material. The experiment shows that the pitch flows very slowly through the opening - about one drop per decade. Its been running sonce the early 1930's and still going.
If you strike this material with a hammer it shatters into pieces like a block of glass.
So what is yield stress? Techincally its the stress that must be overcome in order for a fluid to begin shearing or flowing. But what if it takes decades for the flow to be measured? An apparentlt sold material is flowing!
Weird stuff