Apr 6, 2016 | No Comments | By Andrew Robinson

  • Cutting and notching three-point bend samples for the APS trip
    • We had to machine our own samples from the bulk tile 8 due to the short notice, but the samples are turning out relatively well. We are using the new Allied Hi-Tech Products High Speed Saw with the diamond resin bonded blade. The saw is being pushed to its limit (the cooling water is steaming), but it is still within the safe operational range, and is turning out to be a pretty effective tool. If we get an undergrad well trained on using the saw, its possible that it could be used in conjunction with polishing to save a lot of money over Bomas machining costs for ceramics. They still have chips on the top and bottom that we do not have time to remove or polish off, but these are on the opposite surfaces from the notch, and in the corner so they probably won’t affect the stress state too much.
    • Notching the samples with the diamond wire is also taking a long time especially for B4C. After rebuilding the diamond saw, and fixing its rusted threads, it is running smoothly. We also added a translation stage so we have a full 6-DoF setup (3 rotational DoF for the sample mount, 3 DoF for sample x-y-z translation). This setup has now allowed us to control the depth of the cut by varying the preload we put on the wire. This is done by translating the specimen into the wire by some amount usually around 500-2000 microns depending on the material and desired notch length. Using this setup, we spent about a day calibrating the saw by cutting glass slides to find the right preloads and cutting times for certain notch lengths in glass. We then used these numbers to inform our cutting of quartz and fused silica. For B4C, the effects of preload and cutting time change as a function of the wire lifetime because of the high wear caused by cutting B4C. Because of this high wear, we have to replace the wire for each new notch in B4C. B4C cuts at a maximum of about 1mm/ hr, but for higher quality cuts and less chips, ~800 micron/hr works better. Overall, we should be done notching the samples we currently have by Thursday. Then, on Friday, the new correct orientation single crystal quartz samples come in, and we will start notching as many of those as possible before the trip. It seems that we cannot bring the diamond wire saw with us to APS, so we are planning on training Todd’s post-doc Yunghao on how to make good notch cuts so he can notch samples Sunday and Monday. He will then express mail us the rest of the notched specimens while we are at APS.
  • Starting to write thesis
    • Introduction outline
      • Motivation: Mention Cheyenne mountain bunker as example, easier to dig into rock, and use rock as the bunker material instead of pouring equivalent concrete thickness. Thus, high rate deformation processes in rocks need more understanding.
      • Deformation processes during impact: Focus it down to dynamic fracture by end of paragraph, and discuss why intermediate rates are important to study (there are a gradient of strain rates in an impact, so we are studying the lower end).
      • Discussion of strain rates and loading devices for the different strain rates. Mention some of Wayne Chen and Bo Songs work. Motivate why we are using a piezo driver instead of other options (accuracy and range of adjustability for small samples).
      • Ways of quantifying fracture: Mention ASTM standard C-1421. Then go into Dan Casem’s 2015 paper on 3pt bend samples. Finish with discussion of the strain rates observed in Dan Casem’s experiment, and why we are performing similar experiments but with a notch. This will then lead into the experimental techniques section.
      • Overall, still need a little advice on what the literature review should focus on because it could go multiple ways. Because a lot of the design is driven by what can be found off the shelf, should I reference manufacturer documents?

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