Data!
I finally have the test data! However…
The graphene group actually had an average ultimate tensile strength about 500 psi lower than the standard group. I have a few ideas why we got the opposite of what we hoped for.
Here’s the data summary:
| Standard | Length (in) | Width (in) | Thickness (in) | Cross-section (in^2) | Failure Code | Max stress (psi) | Max strain |
| C1 | 8.40625 | 1.127 | 0.098 | 0.110446 | AAT | 43476.45003 | 1.65E-02 |
| C2 | 8.5 | 1.127 | 0.094 | 0.105938 | LGM | 43637.78814 | 1.57E-02 |
| C3 | 8.5 | 1.115 | 0.095 | 0.105925 | LAB | 45289.59169 | 1.63E-02 |
| C4 | 8.46875 | 1.118 | 0.097 | 0.108446 | LGM | 42518.85731 | 1.56E-02 |
| C5 | 8.40625 | 1.119 | 0.096 | 0.107424 | |||
| C6 | 8.40625 | 1.124 | 0.095 | 0.10678 | LAT | 43896.14984 | 1.61E-02 |
| C7 | 8.46875 | 1.128 | 0.095 | 0.10716 | AAT | 44714.36599 | 1.58E-02 |
| Avg | 8.450892857 | 1.122571429 | 0.09571428571 | 0.1074455714 | 43922.2005 | 1.60E-02 |
| Graphene | Length (in) | Width (in) | Thickness (in) | Cross-section (in^2) | Failure Code | Max stress (psi) | Max strain |
| G1 | 8.28125 | 0.951 | 0.102 | 0.097002 | AAT | 41729.03651 | 1.62E-02 |
| G2 | 8.375 | 0.943 | 0.098 | 0.092414 | LGB | 44708.59394 | 1.63E-02 |
| G3 | 8.34375 | 0.946 | 0.096 | 0.090816 | AGM | 45246.43235 | 1.62E-02 |
| G4 | 8.4375 | 0.942 | 0.101 | 0.095142 | AAB | 42060.28883 | 1.60E-02 |
| G5 | 8.4375 | 0.949 | 0.098 | 0.093002 | LGT | 43531.32191 | 1.55E-02 |
| Avg | 8.375 | 0.9462 | 0.099 | 0.0936752 | 43455.13471 | 1.61E-02 |
The “Max stress (psi)” column shows the highest stress each sample had before it broke.
I’m fairly sure the reason the graphene didn’t help has to do with its quality and the way it was mixed in. First of all, that graphene oxide container was about 8 years old. By the time I was working on it, the water that held the graphene had mostly evaporated, leaving a black paste. In order for the graphene to do its job structurally, it’s best to have many nanoscopic particles. Without the water, the graphene clumped up into much larger particles. I even saw this under a microscope and when I diluted the graphene paste.
I knew I was starting off with a poor graphene dispersion. Refilling the container with 91% isopropyl alcohol and mixing it probably didn’t do much to return it to being separated at a nanoscopic level, but it did return it to roughly its original concentration. Since we didn’t have a sonicator, which is often used to disperse the graphene, we tried putting the container into a bath in a sonic cleaner. It’s unclear whether that did anything because the solution was always an opaque black liquid.
The way I mixed the graphene into the epoxy may have also caused some problems. Note that I had to use 91% isopropyl alcohol–not 100% or 99%. The other 9% is water. Epoxy generally doesn’t like water, and it tends to be weaker if water gets in. Isopropyl alcohol is nice because it evaporates away easily. I also vacuum bagged the composites while the epoxy was curing, which should have helped bring out any water or alcohol. Even then, there still could have been a little water or isopropyl alcohol .
Finally, I cut the graphene group the day I tested it. I only found out after testing that the water from the saw can get into the glass fibers inside the composite, causing them to expand. This might have caused the composite to be slightly weaker during testing because it didn’t have a chance to dry out.
Although right now it seems like I didn’t get the results I had hoped for, I still have a lot of useful information to keep looking through.