156B Week 7

Overview of Status of Analysis, Design, Fabrication, Tests, etc.

• • Fabricating full-length prototype for cast

    • Issues manifested while scaling up; most issues solved by controlling impulse sealer heat

  • Testing solution to grain bunching (two pouches instead of one)

  • Troubleshooting persistent nozzle leakage with RTV

  • Characterizing coffee modulus of elasticity to determine ratio of grains to layers

Parts Arrived:

• • Carbon Fibers

Parts in Shipment:

• • Ball valves

  • Nozzles

Accomplishments from Previous Week

• • Tested full length cast with a single, vertically-segmented grain pouch and double grain pouch to reduce bunching

  • Fixed leaks in cast with vertically-split grain pouch and tested for 75N at 10mm deflection

  • Initial tests for cast with two grain pouches but with everything else constant tested for 40N

    • Tested again for 60N

    • Hypothesized that the discrepancy between the two tests was caused more by the difference in how tightly the cast was rolled around the cylinder than the difference in grain pouch types

  • Fixed issue with Instron which prevented raw data from exporting properly

Goals for Next Week (list names after each item). Use specific and measurable objectives.

• • Testing carbon fiber with grains (Olesya)

  • Determine the modulus of coffee by 3 pt. Bend test (Brian, Dylan)

  • Quantify vacuum magnitude with vacuum gauge (Olesya)

  • Compile testing results in PowerPoint (Kerrianne)

  • Use metal mesh (chicken wire?) to retain cylindrical shape (Kerrianne)

  • Refine length of coffee pouch so it wraps fully around (Kerrianne)

  • Research layer manipulation methods, including origami and steaming (Dylan)

  • Research additional layer type that can be added outside paper layers (Kerrianne)

    • Can use softer and more conformable layers to increase thickness without running into bending resistance issues

Sponsor Comments from Last Meeting and Actions Taken to Address these Comments

In Person (2/20/18)

• • • Could determine modulus of coffee from three-point bending test on an Instron

      • Learned how to conduct 3pt. Bending test through Intron

    • Test different wire gauges/metals for increasing stiffness based on Young’s Modulus and ductility?

      • It may be better for the report to stick with copper and analyze whether increasing number of copper wires adds a predictable amount of stiffness

      • Other ways to improve documentation: quantify vacuum pressure and optimal layer:grain ratio for high stiffness while maintaining conformability    

    • Frame the last section of the quarter as improving the layers through shape manipulation:

      • Origami (lizard tail, Yoshimura folds, Giotto’s circle, Chicken wire tessellation, http://rsos.royalsocietypublishing.org/content/2/9/150067)

      • Vapor Diffusion (steaming)

    • Shear thickening fluids as armor

      • Only flows when moving slowly, so rapid cast deformation would be prevented

        • Good: Sudden impacts that would severely deform the cast meet greater resistance from the fluid

        • Bad: Shaping the cast to the patient’s arm would have to occur slowly

Instructor Comments from Last Meeting and Actions Taken to Address these Comments

In Person: (2/15/18)

• • • Suggested finding a way to modulate the layer hinges, containing them in separate areas so that they don't move while still allowing them to share the same vacuum

      • Possible sealing solutions include:

        • Hair straightener

        • Longer impulse sealer; the one we have now is 12in, others go up to 20in     

        • Hot wire covered in Teflon

        • Using material sealed with chemical bonds instead of mechanical bonds

          • Rubber that seals through vulcanization

          • Flexible PVC: may not come in sheets, but does come in tubes. Can be sealed with PVC cement

          • Research what life vests are made of and how they are sealed; they also must be leak-proof by design

    • Comments on thickness vs stiffness analysis:

      • When only considering load force, increasing thickness by a factor of n increases the stiffness by a factor of n3. However, the following must also be considered for useful analysis:

        • Bending moment as thickness increases, and its effect on stiffness

        • Neutral axis location

          • Requires a modulus for coffee grains

Comments from Other Students in the Class (indicate date of comments and if via email or in person)

• • N/A

Risks and Areas of Concern

• • N/A

Resources or Information Required but not Available

• • Ball valves

Schedule

Budget (list amount spent and amount remaining)

• • Amount remaining $2199.22, $200.78 spent

Progress on Report and Webpage

• • Front page of webpage is done except for final design and some additional drawings/pictures

  • Added an outline for final design’s fabrication steps

  • Continuing revising report based on instructor/TA comments