Overview:
To match conditions similar to those expected from the high speed flight, a propane blowtorch will be used to heat small samples of different materials with different ablative coatings (see test matrix below) while a thermocouple will monitor the surface temperature of the materials. The mass and thickness of the samples will be measured before and after the test to determine the effectiveness of the ablative coating used. A test stand has been built to hold the propane blowtorch at a specific distance from the samples (which can be adjusted as necessary).
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| Fiberglass- CONTROL | Fiberglass + Phenolic Microballoons | Fiberglass + High-temp | Fiberglass + Microballoons + Paint | Phenolic | |||||||||||||||||||||||
| 5-Layer | 10-Layer | 5-Layer | 10-Layer | 5-Layer | 10-Layer | 5-Layer | 10-Layer | ||||||||||||||||||||
| 2-1' | 2-2' | 2-3' | 3-1' | 3-2' | 3-3' | 4-1' | 4-2' | 4-3' | 5-1' | 5-2' | 5-3' | 6-1' | 6-2' | 6-3' | 7-1' | 7-2' | 7-3' | 8-1' | 8-2' | 8-3' | 9-1' | 9-2' | 9-3' | 1-1' | 1-2' | 1-3' | |
| Initial dry mass (no hole) - oz | 0.135 | 0.130 | 0.150 | 0.290 | 0.295 | 0.280 | 0.140 | 0.150oz | 0.160 | 0.305 | 0.300 | 0.305 | 0.150 | 0.130 | 0.135 | 0.295 | 0.280 | 0.305 | 0.140 | 0.140 | 0.140 | 0.270 | 0.270 | 0.285 | 0.785 | 0.780 | 0.780 |
| Initial dry average thickness - mm | 1.016667 | 1.01 | 1.043333 | 2.053333 | 1.996667 | 1.95 | 0.993333 | 0.963333 | 1.083333 | 2.126667 | 2.13 | 2.046667 | 1.093333 | 0.936667 | 0.91 | 1.936667 | 1.84 | 1.886667 | 0.846667 | 0.84 | 0.803333 | 1.75 | 1.753333 | 1.75 | 6.2 | 6.153333 | 6.13 |
| Thickness 1 | 1.03 | 0.98 | 1.03 | 2.08 | 2.02 | 2 | 1 | 1.01 | 1.06 | 2.26 | 2.05 | 2.01 | 1.07 | 0.92 | 0.88 | 1.92 | 1.83 | 1.85 | 0.79 | 0.84 | 0.84 | 1.8 | 1.8 | 1.78 | 6.18 | 6.16 | 6.14 |
| Thickness 2 | 0.97 | 1 | 1.06 | 2.02 | 2.02 | 1.94 | 1 | 0.94 | 1.07 | 2.08 | 2.16 | 2.06 | 1.16 | 0.92 | 0.91 | 1.94 | 1.85 | 1.89 | 0.86 | 0.85 | 0.81 | 1.75 | 1.74 | 1.74 | 6.21 | 6.15 | 6.12 |
| Thickness 3 | 1.05 | 1.05 | 1.04 | 2.06 | 1.95 | 1.91 | 0.98 | 0.94 | 1.12 | 2.04 | 2.18 | 2.07 | 1.05 | 0.97 | 0.94 | 1.95 | 1.84 | 1.92 | 0.89 | 0.83 | 0.76 | 1.7 | 1.72 | 1.73 | 6.21 | 6.15 | 6.13 |
| Initial wet mass (no hole) - oz | |||||||||||||||||||||||||||
Test
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<insert pics>
Setting up thermocouples
Samples
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Procedure:
- Testing in blast chamber
- Heat for approximately 12 seconds
Below are some pictures of the test stand, thermocouple used, Serial Monitor showing that the thermocouple works, and the fiberglass samples used (before they were cut and ablative coating was added)
Test #1:
Test #2:
Improvements for Next Tests:
The first thermal test we conducted was on a single 5-layer control sample of fiberglass (using West Systems epoxy). The purpose of this test was simply to see what improvements needed to be made for the next test, during which more samples will be tested. Below are photos of the sample after the test, as well as a graph of temperature vs. time.
Test Details:
- A thermocouple was attached to the back of the sample with Kapton tape
- The blowtorch was positioned 10cm away from the sample
- The sample was heated for approximately 12 seconds
- The exhaust in the blast chamber was turned on
Observations:
- The sample caught fire during heating, and remained on fire after the blowtorch was turned off (eventually self-extinguished)
- The epoxy holding the layers together was burned (and off-gassing was observed) but the epoxy within each layer seemed to be intact.
- The thermocouple (attached with Kapton tape) separated from the sample during heating. This is the likely cause of the small step observed in the graph below.
Improvements for Next Time:
- Videotape each sample the entire length of the test (in case anything interesting happens after the blowtorch is extinguished, for example)
- Bring an IR sensor to detect the flame temperature
- Attach the thermocouple more securely/consider a different method of attachment so it stays on the sample
- Have a camera on both sides of the sample
- Note the start time on the serial monitor (Arduino) to keep track of when the flame was turned on/off
- Increase the distance between the blowtorch and the sample (measure temperature of air vs. distance of thermocouple from blowtorch, and temperature of flame itself)
- When preparing the samples (fiberglass layup), use a flatter surface so that the average thickness is more consistent
- If testing high-temp paint, use more than one coat so that there is enough paint to show results
- Find some way of remote-triggering the blow torch for added safety
- Use a more accurate scale so that initial and final mass is more accurate
- When measuring thickness (for average thickness calculation), be consistent when choosing points to measure on the sample, and take more than three measurements for a more accurate estimate
- Use thermocouple with thinner tip for more accuracy
Test #2: