Ice691: double sample, 3 x P-drop f.g. ice I + 10% by vol 0.3-micron Al2O3
  Top piece: WBD method
  Bottom piece: DLG method
  Cold press 2 hrs at 120 MPa, 210 K
   
T = 210 K, P = 50 MPa, s = 6 MPa step (1)
T = 210 K, P = 50 MPa, s = 8 MPa step (2)
T = 210 K, P = 50 MPa, s = 12 MPa step (3)
before compaction
after compaction, before def, 0,90 degree views
after step (2), 0, 90 deg
after step (3), 0, 90 deg

run log
687, 691 working plot

 

Legend: Upper graph of each pair is motor speed V (proportional to edot); lower graph is load (in volts). Translate motor V to edot thus: V0.02 ≈ 3e-7/s . Load to stress translation for ice687 is roughly 0.25 MPa/mV, with a 5 mV zero offset. Horizontal scale is time. 5000 ≈ 14 hrs.
     
e=0.114

Tues afternoon. End step (3) at 5% additional strain. edot chart started to show acceleration--so there was some worry about mechanical instability--but then it dropped down again.

Weds a.m., about to start step (4), and the jacket developed a leak. The bulging jacket around the bottom end cap (rightmost photos above) was worrisome.
e=0.097

Tues 2/26/13 midday. Step (3) underway. Steady and significant strain hardening for first ~3% strain has leveled off over the past hour at 1.8e-6/s. 10x increase in strain rate for 1.5x increase in stress =>n ≈ 5.5. What is going on in this stuff? Might be interesting to go back to step (2) condition after this for a clue about the cause of the extended transient and the high n: a big change wrt step (2) usually means the existence of back stress (e.g., from elevated dislocation density); a small change suggests a mechanism change between (2) and (3).
e=0.066

Mon morning 2/25/13. End step (2b). edot ~1.8e-7/s over past 12 hrs. Sample comes out now for shape measurements.

Quick length change measurements on images above say the ratio of avg strain rates on top T and bottom B samples is 1.42. Diameter measurements say the T/B stress ratio (=1/area ratio) was 1.16 at the start of deformation (and not much different, 1.18 at the end). This ratio of conditions in the T and B samples is represented in the working plot above by the short slanted line through the two points plotted at mean conditions.

If T and B are rheologically identical, then n =log(1.42)/log(1.16) = 2.1. On the other hand, if T and B have the same n=4 as run 687 but have different pre-exponentials, then the strain rate ratio should have been 1.16^4 = 1.8; the fact that it was 1.42 would mean the B material is stronger than the T at these conditions.
e-0.059 Late Sunday. Continue step (2b). edot ~1.5e-7
e=0.053 Sun late morning. After backing off piston for zero check of force gage (was ok), continue step as (2b). After 60-90 mins, edot has settled back to where it left off.
e=0.052 Sun 2/24/13 morning. End step (2). edot still close to 2e-7/s, slight to no strain hardening over past 24 hrs. The first ~4 hrs of this 12+ hour record actually show a small amount of strain softening. May not be significant given ±0.2 K T variation and other extraneous things.
e=0.043 Sat evening. Step (2) continues.
e=0.039 Sat, midday. Step (2) continues, as does strain hardening. Avg edot since previous shot 2.1e-7/s. This is now only 3x faster than at the end of step (1), meaning apparent n < 4.
e=0.034 Sat 2/23/13 am, ~13 hrs later. Steady work hardening. edot averaged 3.3e-7/s over first ~6 hrs of this trace, 2.8e-7/s over most recent 6 hrs.
e=0.020 Fri ~1800 hrs. Start step (2), which takes off way faster than expected, 4.6e-7/s over the 2nd half (~past 2 hrs) of trace. 6x increase in edot for only a 33% increase in stress => n > 6!
e=0.013 Fri ~6 hrs later, end step (1). edot 7.4e-8/s over past 6 hrs. This edot is way to slow to get to 5% by Mon am; brief email discussion about raising s in next step...
e=0.012 Fri 2/22/13 early. Step (1) continues. edot ~2x slower than expected, slight but steady strain hardening throughout.
e=0.007 Thurs 2/21/13 pm. Step (1) underway. Currently somewhere in the neighborhood of 4e-7/s at 210 K and 6 MPa. Differential stress in the DLG portion is roughly 15% lower. Ignore the bounce in the stress in the lower trace as I work through some LN difficulties.
  Check out early start at ~2.4 MPa, through pt. ~600. edot ≈ infinity^-1.