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).
The tests will be performed in a secure environment (blast chamber) and the operators will wear respirators during the tests. This document from Apogee Components was used as inspiration for this test procedure. Apogee Newsletter
Materials Used:
- Fiberglass
- West Systems 105 epoxy (resin + hardener)
- Phenolic microballoons
- POR 15 High-temp Heat Resistant Paint
- 400-grit sandpaper
- Small popsicle sticks
- Mixing boat for epoxy
- Dremel
- Worthington propane blowtorch (14.1oz)
- Arduino Uno
Thermocouple Amplifier MAX31855 breakout board (MAX6675 upgrade): https://www.adafruit.com/product/269
K-type thermocouple: https://www.adafruit.com/product/270
Jumper wires
- Breadboard
- Test stand
- Calipers
- Mini scale
- Gloves, respirators
Below is the matrix for samples used in this thermal test. All samples measured ~2" x 2" (with thickness depending on the sample), and there are three samples for each combination (for three trials).
| 1/4" phenolic sheet | ||
| 5-Layer Fiberglass | 10-Layer Fiberglass | |
|---|---|---|
| Control (West Systems epoxy) | ||
| West Systems + Phenolic microballoons | ||
| West Systems + Cork microballoons | ||
| West Systems + High temperature paint | ||
| West Systems + Cotronics 4700 | ||
Fiberglass Sample Preparation:
- Used West Systems epoxy to make 4 of 8" x 8" sheets of fiberglass (2 x 5 layers, 2 x 10 layers), making sure to put Mylar beneath to keep the samples from sticking.
- Let the samples cure for at least 24 hours.
- Sanded with a Dremel, then with 400-grit sandpaper. Make sure to sand the shiny side as well.
- Mark and cut into 1.5" x 1.5" squares.
- Recorded dry mass of each sample (series 1-9)
- Took three measurements of thickness on three different sides, and calculated/recorded average thickness (series 1-9)
- Wearing respirators, mixed 50 g. West Systems resin + 9 g West Systems hardener (100:18 ratio for West Systems, but this depends on the epoxy you choose to use)
- Mixed in phenolic microballoons using a popsicle stick until a consistency slightly thinner than peanut butter (like melted ice cream) was reached.
- Applied an even but thin layer of phenolic mixture to samples (series 4, 5, 8, 9) using popsicle sticks
- Let samples cure for 36 hours.
- Wipe samples with acetone to remove any dust or debris.
- Recorded average thickness of samples with phenolic coating (series 4, 5, 8, 9)
- Sanded with 400-grit sandpaper then recorded mass (and wiped with acetone)
- Applied high-temp paint to fiberglass samples (series 6,7) and fiberglass + phenolic samples (series 8,9)
- Let paint dry for at least 24 hours (depending on what paint you use)
- Wipe samples with acetone to remove any dust or debris.
- Record mass of each sample (series 6, 7, 8, 9)
- Record average thickness of each sample (series 6, 7, 8, 9)
Below is the test matrix for the parameters measured during this test. (MAKE SUMMARY, ATTACH EXCEL FILE).
| 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 Stand
<insert pics>
Setting up thermocouples
Samples
Test Procedure:
Testing in blast chamber
Heat for 12 seconds
Improvements for Next Tests:
- 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
