About the project
I created this impact strength tester after realizing that there were no good ways to compare filaments across manufacturers, as they used different testing methods. For example, PolyMaker PolyMax PC on PolyMaker's website had around half the impact strength of the same filament on Prusa's website. However, I didn't have my own Charpy impact strength tester, so I decided to make my own that would at least allow me to compare filaments, and I hope to help the FTC and 3D printing community a little with this. It uses tubes from FTC fields and a 3D printed frame, to allow a weighted tube to drop down onto the notched test piece. The total weight of the tube is 310 grams.
What counts as broken?
For the purposes of this experiment, I am defining broken as either completely broken in half, or bent so badly the test piece falls out of the holder. While there is slight bending and stress marks way before it breaks in half, this allows the test to measure how the material performs under continued stress, even if it is slightly damaged.
The testing process
To test each filament, I drop the testing rod higher every time in 1 inch increments, until the testing piece breaks or the height goes past 21 inches (the maximum height). This allows the test to also measure the resistance to repeated impacts, not just a single hit. I take the average of 3 trials.
Results
Intrestingly, PolySonic is the most impact resistant while PolyMax is supposed to be more impact resistant. The failure mode every time for PolyMax was bending out of the holder, not breaking in half. This shows that too low of a stiffness can have drawbacks, and it had stress marks all over the test piece. While this test does give some information, the notch to plastic thickness ratio is way bigger than on a real Charpy impact test. This causes it to test how a material responds to repeated bending force rather than pure impact strength.