The rock and ice mechanics lab at Lamont-Doherty is led by PIs Heather Savage, Christine McCarthy and Ben Holtzman. We are in the process of growing our lab and building our experimental program. Along with a team of postdocs, undergrads, grads, and longtime staff engineer Ted, we are rehabilitating and revamping some of the old equipment and building new rigs for exciting new experiments on both rock and ice. You can follow along with our progress here.
After the dry run was complete, it was time to move on to the real thing: ice-on-rock. Mike made a plexiglass front to the cryostat so we could watch what was happening and still keep things moderately cold (also thanks to our friends burlap and bubble wrap). Here it is in its "double direct shear" starting position...
...and afterward. We successfully slid ice past rock with an applied normal load (~100kPa)
A toast of champagne to celebrate!
And a paper describing the apparatus is found here.
Before we start getting crazy with ice and cold, we want to have a dry run of the apparatus. Can we actually control it the way we want? We loaded everything up in the cryostat, but left it at room temperature with the front panel off and, instead of ice, we placed a piece of PVC plastic as our central slider.
We used some makeshift plastic pistons so as not to potentially harm our expensive ceramic ones.
We manually dialed in our horizontal piston until we got a decent normal load (the panels that say 0.167 and 0.160 are in MPa and are the right and left load cells, respectively).
Then we slowly drove the plastic down through the rock. Plastic is pretty slippery, so we didn't get to very high shear stresses, which made me very happy for a first run. It all worked in a nice controlled manner, with data sent to a computer for later analysis. No major glitches, so next step: ICE!!
Now that the rig has been placed in its permanent position and the unistrut table has been bolted down to the concrete pier, it's time to address the elephant in the room. Let's talk about that rat's nest of wires.
Yeah I'm talking about you.
First thing we did was to systematically tackle each wire and cut it to the length it needed to be.
Then all the gray component wires (those going to the LVDTs and Load Cells) were tucked into this plastic housing and attached to the back edge of the lower plate. (That the channel housing is the same thickness as the plate was rather satisfying).
Then the wires coming out were wrapped in fancy black plastic. We are talking next level organization here.
Isn't this the tidiest thing you've ever seen?
No need to stop there. The chiller hoses needed to also make a clean profile.
They carry a methanol/water mixture from the programmable chiller in the next room to the cryostat.
So we started doing some calibrations in the apparatus and realized we would like it just a bit stiffer. We decided to put another steel plate, this time to reinforce the bottom plate. But we couldn't just slide it in. The horizontal hydraulic piston and the cryostat dimensions were all designed around the current space between top and bottom. Instead we had to lower the bottom piston the same amount as the new the steel's thickness and then slide in the plate. This required us to lift up the whole rig from the top. A mobile hydraulic crane did the trick.
While we were at it, we reconstructed the unistrut table that the rig sits on. We not only shortened it to account for the rig adjustment, we also repositioned the legs so that they were symmetric. Much prettier.
Here Mike tightens down the steel plate with an allen. He also built the housing for a lower LVDT (the rounded square on posts beneath the rig) that will measure the position of the sample as it slides.
A spring loaded LVDT will come up through a hole in the plates and cryostat. A ceramic extender piece sits right on top of the spring loaded core and will actually be in contact with the ice.
At the risk of repeating myself…we're almost there.
I'm here in Berkeley, CA, at the CIDER summer workshop. We've got a great group of students, postdocs, and guest lecturers in attendance. The topic of the workshop is "Solid Earth Dynamics and Climate - Mantle Interactions with the Hydrosphere & Carbosphere", so we have a broad swath of scientists who study everything from glacial adjustment, paleoclimate, geochemistry, seismology, geodesy, and geology.
I don't know anything about the hydrosphere or the carbosphere, but those "in the know" assure me that the way these components travel through the earth is highly dependent on the rheology of rock. So Uli Faul (from MIT) and I are giving lectures on Rheology, as well as a hands-on rheology tutorial.
For the tutorial, we decided to let students perform a creep experiment in real time. The students broke up into 3 groups to perform creep experiments on 3 different types of cheese. During the week I went with Michael Manga (from UC Berkeley) to raid his machine shop for different weights to place on top of the cheese. We gave each group 3 different size weights so that, in theory, they could come up with a flow law for their cheese. Here is Team Havarti. They were unfortunate enough to be given very tall, unstable weights. Despite this, they did a great job of collecting the data as the havarti shortened.
Here is Team Gouda. After unwrapping the classic red wax, they discussed a plan and started measuring.
And finally Team Jack, with the heaviest weights.
Despite huge error bars in estimating stress (which they had to do by calculating the volume of the cylinder and the density of the metal - but what about those holes?) and uncertainties in measuring shortening with little rulers, the groups came up with surprisingly nice creep curves. Here is my favorite curve, the one for Gouda at the lowest stress. The team didn't quite capture the immediate elastic response, but they got everything else. At about 1900 seconds, they removed the weight, so that is the relaxation portion of the curve at the right.
Although it was challenging with so few data points, I estimated a strain rate for every curve that the students gave me. Quite shockingly, the strain rate vs. stress curves were quite nice. I included my muenster data from the trials at home.
The n=1 slope in log-log space indicates that the deformation is Newtonian. If this was a polycrystalline material, I could say that it was deforming by diffusion creep. However, in the case of cheese, it has to do with proteins and fats and I really have no idea what is happening at the microstructural level. But the curves are nice. Great job everyone!
Next week I will be heading to Berkeley for the CIDER meeting. I've been asked to give a tutorial and lecture on the subject of rheology. For the tutorial, I want to let the students perform a creep experiment in real time. Rock and ice would each take too long to deform and would be a hassle to maintain at the right conditions. However, Ben Holtzman reminded me that cheese could be a perfect medium for a one-hour creep experiment. This week I want to give it a dry run or two, to make sure I can work out all the kinks.
Following our usual philosophy of experiments, I cut out various samples of Muenster and Gouda with a width to length ratio of roughly 1 to 3.
I found small cubes and rectangles of aluminum in the scrap drawer and placed them on top. Crash! Not only did the tiny aluminum not have enough heft to start any deformation, this configuration was completely unstable. They all tipped over. Back to the drawing board.
This time I will make the samples wide and short and I will get much denser metals for the weights. First I make sure to get all the dimensions of the cheese. The initial height will be used to calculate the strain as the cheese shortens. The contact area of the block on top of the cheese (I tried to make them the same size) will be used to calculate the applied stress.
Okay - this configuration works much better. The two brass pieces on the muenster weren't totally stable, but they still did the trick; despite their leaning to the side for half the experiment, we were still able to get a good creep curve:
Look out CIDER, here I come! (but now how am I going to lug all these weights in my suitcase?)
Now that the cryo-friction rig is finished, we are running through a litany of calibrations and tests using standard materials. During this process we realized that the stiffness of the rig needed improvement. Our 1" thick aluminum top plate was deflecting a small amount with large load. Even though that load is probably bigger than our usual load will be, we still want a very stiff apparatus for friction experiments. So we have added a 3/4" steel plate to the top, between the plate and the piston.
We bought some pieces to act as spacers and square washers to clamp down on the plate using the existing nuts and tie rods.
But the pieces that we ordered weren't the right size, nor even uniform in size. So we had to cut and then sand them all down. New undergraduate intern, Channing, helped with this process. First he carefully sanded each one on the belt sander, measuring after each sand.
And then he installed the pieces and washers to the rig. I can't wait to see the improved stiffness measurements!
Every spring in Japan, the cherry blossoms ("sakura") bloom for a brief period and everyone has a party. They go to parks, spread out blue tarps under the cherry blossom trees, bring snacks, drink, and contemplate the cycles of life. The party is called "hanami" (hana = flower; mi = see or look at). Last Spring I was in Tokyo for research and was fortunate enough to attend several hanami. Back home at Lamont, we actually have a row of cherry blossom trees just outside our lab.
This spring grad student Hannah Rabinowitz successfully completed her oral exams just in time for the cherry blossoms to bloom. So we decided to have a party for her…our own "Hannah-mi". Ted found the perfect big blue tarp and we all brought our favorite treats. Despite the chill, we spread the tarp out beneath the blossoms.
There we had a bit to eat…
…and nearly froze to death. Ted wisely snuck off to set up a space in the lab to spread out all the Japanese treats (wasabi seaweed, senbei, and sake) and we concluded our party in the warmth of the lab...
...enjoying the cherry blossoms from the other side of the window.
Previously I reported about Sarah's desktop reaction driven cracking experiments. Well, based on some really nice results that she is currently writing up, she's decided to scale up the experiment and perform it in the triaxial apparatus. First step is preparing the samples for loading. The most important thing to worry about is that they are leak tight, since she will be controlling both confining pressure and pore fluid pressure. Since she is going to be monitoring several more things than has been done in the past (including acoustic emissions and a furnace), she's got a lot of wires on there and keeping things tight was no trivial feat. After a couple of mishaps earlier in the week, on Friday she sealed up a sample, tested it for leaks on the bench top...
…and loaded it into the triax.
Ted monitored everything from the next room. After a nerve-racking hour or so of ramping up the confining pressure, it became clear that the procedure was a success! She now has the protocol for loading up the air tight samples and will commence the reaction driven cracking experiments. Go Sarah! And this all happens just in the nick of time: in June Sarah will be leaving us for UC Davis where she will start a lectureship position. Congratulations, Sarah!
Oh Vienna, home to so many dessert options. No sooner did I get off the plane and drop my bags in the hotel, did I find myself in the hotel bar enjoying the first of many cakes for the week.
The reason I found myself in Vienna was of course for the annual European Geological Union meeting. We Americans can't usually spend the funds to attend this meeting with any regularity. So those few times when we are invited to attend for a special session, it is a real treat. In this case, there was a session on Microstructures and Deformation Mechanisms in Ice, which received a little bit of funding from Micro-DICE in order to bring together researchers from around the world to compare notes and talk about what we are doing.
Our session was assigned one of the brand new PICO formats, which stands for Presenting Interactive COntent. At the designated time we all met at one of three bright orange PICO stations for the brief oral portion of the presentation. Since I came from so far, they gave me a ten-minute time slot to open up and introduce the session. Then the rest of the researchers went through "two-minute madness" in which they gave the highlights of their work and showed how their particular interactive poster worked.
After the "madness", we all stood in front of big touch screens to navigate and host our interactive poster. Although the content for an interactive poster involves many, many interlinking powerpoint pages (mine had 30 pages; the "sample" they sent us had 60!!) and was incredibly time-consuming to prepare, I kind of liked it. It was challenging to come up with this new, non-linear way of presenting data. I think it is probably going to be the wave of the future, with posters able to be navigated in our absence, so it was fun to be an early user. And since the session was on Monday, that left me time to enjoy the rest of the meeting and even sneak out a bit to see some of Vienna. Of course, that included a bit (read: heaping mounds) of the local cuisine.
Huge progress in the lab today. The last month or two have been filled with a whole lot of calibrating, adjusting, wiring….
…testing, cross testing and multi component cross testing. Ted has been working his butt off getting all the electronics to talk to each other just right, getting all the limits and failsafes to do their job, and fixing last minute hydraulic leaks.
And this afternoon, we had the load cells and LVDTs hooked up and the electronics driving the hydraulics pistons. We can make it move up and down on command, in either load or position control. This is huge! THE LDEO CRY-AX IS ALIVE! We can now start squeezing and sliding the heck out of stuff! Yeah!