text

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.

Friday, 26 June 2015

Getting ready for CIDER

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?)

Monday, 1 June 2015

Improving the apparatus stiffness

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!