Junior year in college for a soon-to-be Mechanical Engineer can be a tough cookie to crack. In the efforts to self-motivate and make lemonade with school lemons, I set myself to do a 3-point bend test on 3D printed polycarbonate. Yes, this is fun to me!
It’s not often that a legit laboratory room is wide open for your own experiment. I was given an opportunity to perform an experiment of my own choice for a Strengths of Materials course at the University of Utah. Of course, I had to create a full professional memo to be graded in return but that’s a good trade, I thought.
Nowadays, many organization and entrepreneurs see 3D printing as a manufacturing method that can go beyond rapid prototyping. Printing end-products has been a fascination of mine. It was no surprise to my laboratory team classmates that I would pitch the idea of doing a 3-point bend test on 3D printed polycarbonate.
Polycarbonate (PC) is one of the many exotic materials able to be printed with an FDM printer. PC is particularly useful when a design requires a tough material, with high strength under impulsive forces. it has great performance under high temperatures and great flexural strength. These properties are typically desired for a mechanical product. The fact that PC not only has these properties but that it is also a thermoplastic that can be extruded into practically any shape through FDM printing makes PC a target material for many new mechanical end-products.
The Test Parameters
There have already been many academic studies done on 3D printed PC, but none that acquired the modulus of elasticity of PC at extreme outdoor temperatures. The lowest temperature that the Flir E6 Thermal Imaging camera we used could record was a minimum of -40 degrees Fahrenheit. It is possible to get this low temperature at the surface of the earth, so it was chosen as the low-temperature parameter. There was also a room temperature specimen that would serve as a control and would be compared to the Stratasys material specification sheet and a high-temperature sample that that would be heated as uniformly as possible. Liquid nitrogen was used to cool the cold specimen, and a heat gun was used for the heated specimen.
Below you will find the results table which also contains calculated values from the specimen parameters (i.e. the moment of inertia). It was interesting to see how the modulus of elasticity was higher for the cold specimen, and lower for the hot specimen relative to the control. This makes sense for an engineer since as a material is cold, it should become “stiffer” and brittle. The hot specimen was more soft and ductile.
|Property/Parameter||Cold Winter Night||Room Temperature||Hot Desert Day|
|Temperature range °F||-39 to -18||71.2 to 73||129 to 104|
|Moment of Inertia (in^4)||0.001361492||0.001380399||0.001345475|
|Max Force (lbf)||109.72||91.67||90.2|
|Max Displacement (in)||1.61||1.5||1.421|
|Modulus of Elasticity (psi)||177338.2||159156.4||153865.9|
|Max Stress (psi)||162950.4||127768.9||119146.1|
There was a high percent error comparing the control (room temperature) specimen with the Stratasys specification sheet. This, however, is due to the different parameters chosen during the print of the specimen sample. You can make a print more rigid by increasing the layer height and print width… Lesson learned!
Great! Now what?
I received my grade and it was a good one too! Now, I plan to use this information to design a high-power First Person View (FPV) racing drone frame that can easily take the abuse of flying around a track at nearly 100 miles per hour.
If you do not know what FPV Drone racing is, I encourage you to see it in action! Lookup “Drone Racing League” in YouTube for a glimpse of what these flying beasts can do. Feel free to use this data for your educational purposes.
I will be posting a few more blogs about my drone frame progress so stay tuned! Do you want to see the technical memo about this experiment in all its nerdy and verbose glory? Please comment below or ask me if we cross paths on a technical support call.