(03-23-2017, 09:40 AM)grepper Wrote: 1) If I understand that correctly, to maintain a constant Deborah number with a piece of hot or cold steel, the rate of deformation would have to be much slower for the piece of cold steel compared to that of the the hot steel. Correct?
2) Is it true that even though steel is not exactly what I would consider a fluid, apparently it can actually relax enough over some period of time that fatigue could occur without hardening?
3) Practically, what period of deformation are we talking about with room temperature stainless steel to induce hardening? 1 per second? Five/second? 1/month?
Ad 1) Yes, Grepper, you are correct!
Ad 3) This question is too difficult for me because I do not have the relaxation time data for stainless steels. Sorry for that!
A frequently quoted example to illustrate this behaviour is the children’s toy “Silly Putty” which is based on silicone polymers.
Pulled rapidly it fractures like a solid while pulled slowly it flows like a liquid. The relaxation time of this polymer is circa 1 s. If rapidly means during 0.1 s, then the Deborah number is De = 1 s / 0.1 s = 10, what classifies the material as solid-like. On the other hand, when slowly means during 10 s, then the Deborah number is De = 1 s / 10 s = 0.1 what classifies the material as liquid-like.
We have very striking situation when our material classification depends on the experimental time! I am attaching an after diner talk by the inventor of the Deborah number.
(03-23-2017, 11:24 AM)Mark Reich Wrote: Jan, Welcome to the forum, it's great to see you jump in with your knowledge here! I've never heard of a Deborah number. From a brief search I could see that knowledge might be beyond my pay grade.
Thanks for your welcome, Mark!
The striking, but universal, concept currently discussed here is successfully applied in Earth Sciences – e.g. seismic hazard calculations. I have only tried to apply it to steels what is not quite common.
The usage of the Deborah name was inspired by the Bible verse "The mountains flowed before the Lord" (Judges 5:5). The basic idea is that everything flows, even the mountains, if you wait long enough!
Jan