Sunday, June 5, 2011

(II) Our Mission ~ Part 1

(A) Tensile Testing of Engineering Materials

Experimental Procedures

Polymer and Metal Tensile Testing:
  1. Measure the cross-sectional are (thickness and width) of specimen by using a caliper
  2. Load the specimen to the equipment.
  3. Lower the specimen to the bottom clamp slowly and tighten it by the hand
  4. Clamp the specimen tightly by the upper clamp
  5. Activate the specimen protection
  6. Set all the readings to zero
  7. Execute the test
  8. Get the data, fill in the following table and plot the graph of Stress vs. Strain using Excel
  9. Remove the Specimen
  10. Finally compare all the three curves in one frame of axes and discuss about the differences.

  1. Why there are variations in the mechanical properties of material of the same type?
  2. Why differences exist in mechanical properties of different materials?
  3. What is the majority difference between polymer and metals in terms of mechanical behaviour?
Bonus Question: Compare the break surface of the 3 samples, guess the relationship between elasticity and break surface.

(B) Scanning Electron Microscope (SEM)

Experimental Procedures
  1. Vent the column and insert specimen
  2. Pump down (evacuate)
  3. Select accelerating voltage, spot size and working distance
  4. Turn on high voltage
  5. Select load current (3-5kv for polymers and 15kv for metals and ceramics)
  6. Turn up filament (touch the orange bar)
  7. Select TV rate
  8. Adjust the image and save.
  1. What do you think may be caused if there is too much moisture on the specimen?
  2. What is the working distance and accelerate voltage if the specimen is titanium?
  3. Why can’t we heat the filament too fast?

(C) Composite Material Processing

Experimental Procedures
  1. Take 5 pieces of the fiber matt.
  2. Weigh the fiber matt and record down the weight of the fiber matt used. In this case we will use 1:1 ratio between fibers and matrix; 5:3 ratio between epoxy and hardener solution.
  3. Arrange the plastic sheet, Teflon sheet and tissue paper in the following way.
  4. Calculate the weight of epoxy required (62.5% x weight of the fiber matt) and record down in the logsheet.
  5. Calculate the weight of hardener solution required (37.5% x weight of the fiber matt) and record down in the logsheet.
  6. Pour and weigh the required amount epoxy into the plastic cup.
  7. Pour and weigh the required amount hardener solution into the plastic cup.
  8. Stir and mix the solution with ice cream stick for 2-3 minutes.
  9. Put the first fiber matt on the Teflon sheet.
  10. Pour small amount of the solution and spread over the fiber surface.
  11. Quickly put the second fiber matt on top of the first fiber matt.
  12. Pour some of the solution on and spread over the fiber surface.
  13. Repeat step number 11-12 for all the five fiber matt.
  14. Quickly cover the fiber matt with Teflon sheet, tissue paper and the plastic sheet as shown in the arrangement in step number 3.
  15. Put on some weight and leave it for 1-2 hours.

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