3D Printing Mechanical testing of 3D printing filaments

[Dustin Lobner]

Hi everyone,

I've been flying 3D printed fincans and nosecones and whatnot, slowly working my way up the power ladder. Memorial day weekend, I flew a J450DM with a printed monolithic fincan/MMT with zero issues (see pic below). I want to switch filaments from what I have been flying (~$60/kg, Tough PLA from Matterhackers) to something less expensive (PETG for $30/kg).

I'm a materials engineer and have access to a mechanical testing lab, so I'm thinking about putting together a "proper" mechanical test program to determine how the properties look for different materials. I have a plan, but wondering if people could comment on things they'd be interested in...not that I'll do everything, but I'll do what I can. I'll report out the results to everyone here. I have access to a universal tensile/compression machine, 200 pound capacity.

The plan:

1) vertically print tensile bars at a variety temperatures and identify the temperature that provides the optimum tensile strength for each filament - vertical print to put weakest plane in tension
2) using that best temp for each filament, print tensile bars both vertically and horizontally at a variety of number of solid outlines and infill %'s
3) same temp for each filament, print hollow cylinders with a variety of conditions and test in compression
4) report out

Pretty simple. Thoughts? Am I missing anything that would be helpful? The biggest one I can think is impact toughness, but I don't have means of testing that. Also perhaps notch sensitivity.

Thanks!

 

[Yukon@K-9 Rocket Tech]

This sounds like a cool plan! I suggest you check out CNC kitchen. He is a engineer who tests filaments, inserts, layer height, infill, and practically everything and see how it effecrs strengths. His videos have helped me with makeing parts stronger, and I'm curious to see your results too!

 

[Dustin Lobner]

This sounds like a cool plan! I suggest you check out CNC kitchen. He is a engineer who tests filaments, inserts, layer height, infill, and practically everything and see how it effecrs strengths. His videos have helped me with makeing parts stronger, and I'm curious to see your results too!

Yeah, I've seen it, thanks for sending along! It's part of the inspiration behind this actually. What I'm planning on is something like that but more pointed at rockets.

 

[Yukon@K-9 Rocket Tech]

Yeah, I've seen it, thanks for sending along! It's part of the inspiration behind this actually. What I'm planning on is something like that but more pointed at rockets.

That's awesome! It'll be super cool! It got me thinking, don't all the fins experience some form of torsion along the central axis of the fin can as a whole if the rocket spins? I'm curious about how layer lines would handle forces like shear or torsion in relation to the layer lines, since most tests seem to deal with single forces applied perpendicular to the layer lines. I would assume near the center point of both forces, the layer liens would either snap or stretch depending on the layer adhesion, but I think it would be interesting. Idk these are just my thoughts and I could be wrong since I'm not a engineer XD

 

[Dustin Lobner]

That's awesome! It'll be super cool! It got me thinking, don't all the fins experience some form of torsion along the central axis of the fin can as a whole if the rocket spins? I'm curious about how layer lines would handle forces like shear or torsion in relation to the layer lines, since most tests seem to deal with single forces applied perpendicular to the layer lines. I would assume near the center point of both forces, the layer liens would either snap or stretch depending on the layer adhesion, but I think it would be interesting. Idk these are just my thoughts and I could be wrong since I'm not a engineer XD

True...I was thinking about printing a fin horizontally and then push down on the tip and measure a) deflection vrs load (stiffness) and b) failure load. I'm pretty sure that would have a direct relationship to flutter resistance. Torsional test would be best, but that's a hard putt with the equipment I have on hand.

Maybe buy a torque wrench and torque a fin until it shatters?

 

[Dustin Lobner]

Quick update - this is happening. Right now, only doing tensile in Z at differing temperatures and then tensile in X at the best extrusion temp. Trialing:

eSun PETG
eSun PLA Pro
Matterhackers Builder Series PETG
GreenGate3D recycled PETG
Matterhackers Tough PLA