Destructive Impact Testing: Markforged Onyx vs Nylon vs Tough PLA

Technical Manufacturing
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#1

TL;DR: I hit some 3D printed parts with a hammer using a quasi-standard method so I don’t have to rely on manufacturer data sheets.

Izod Gif

I’ve read a lot of anecdotal and sometimes handwave-y comparisons of FDM 3D printed materials on CD over the years, but I want to take a step back and quantify some material properties. One thing I’ve wondered for a while is whether the relatively high impact strength of Nylon is worth the extra hassle of keeping it dry. For my first experiment I decided to make an Izod impact strength testing rig while using as many spare parts already on-hand as possible. I’m planning to record other properties eventually.

Here’s a diagram of my set up:

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For the test machine design, I referenced CNC Kitchen’s set up (loosely based on ISO-180) and skimmed through the ASME D638M-95 as well. Using the encoder to record starting angle and post-strike angle before the pendulum swings back, I can determine how much energy a sample absorbed. The starting energy of my set-up is ~ 4 J, as opposed to the ~2.7 J in the ASTM standard or the ~2 J in CNC Kitchen’s set up. My striker also hits the sample roughly ~ 5 mm higher than the ASTM standard. I’m using CNC Kitchen’s test sample model, which has a notch modeled into the part rather than printing a solid part and notching after the fact. All parts were printed with a Dremel 3D45 enclosed 3D printer, except for the Onyx samples.

Without further ado, here are my results thus far:

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At first glance, there’s nothing too exciting (Surprise! Onyx is tougher than PLA+). For my first tests, I printed Dremel-branded “Eco-ABS” (actually a modified PLA) and Nylon samples as well as the Markforged Onyx samples. The Onyx filament was immediately placed in a dry box after opening, per standard procedure. The Dremel filaments sit inside the print enclosure, which isn’t air tight. This lead to the Dremel Nylon results with much more deviation and an average Impact Strength value closer to CNC Kitchen’s results with “conditioned” Nylon samples. I could definitely hear rapid evaporation while the Nylon was printing, but the samples themselves looked fine.

I decided to dry the Nylon roll overnight and re-run the tests, resulting in Impact Strength figures much closer to (and a bit lower than) Onyx. While I was at it, I ran a smaller sample set of Duramic PLA+, which seems be even more impact resistant than the Dremel equivalent.

I still have a lot of questions about Nylon-based filaments and immediate next goal is to print Nylon and Onyx samples and let them absorb ambient moisture for a week or so before running the same tests.

Feedback and suggestions are welcome!

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#2

neat

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#3

Very cool! Have you tried comparing these test results to PETG or ABS?

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#4

Big fan of the homebrewed test rig. That’s some nice work. Giving me flashbacks to my materials class where we smashed into things with a similar setup to get hardness ratings.

Maybe I didn’t see it but what settings were used on the printed parts and which orientation were they printed in? The slicer settings can affect things quite a bit so standardizing as much as possible is probably a good idea. Eiger vs other slicers might make that a little challenging though.

Would be cool to compare other materials too and build up a nice resource. Great work!

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#5

So if I want a really high impact strength part, I should let my nylon filament absorb some moisture before printing? That seems weird to me, but I really don’t know anything about material strengths and such. Anybody who knows more than me about this subject have an explanation for this?

#6

Or after.

Nylon absorbs water and it makes it a bit more flexy but less rigid.

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#7

You had me at “Destructive Impact Testing”

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#8

Nylon can adsorb (yes, adsorb) 9% or a little more of its weight in water. Some formulations are much less. Nylon is quite hygroscopic, meaning it can pull moisture right out of the air.

Having water molecules stuffed into interstitial spaces of the plastic’s structure changes many of its physical properties.
Generally speaking
-Parts swell
-Strength goes down
-Stiffness goes down
-Ductility goes up
-Impact strength goes up

Lots of good charts here: Mechanical properties | AMILAN™ | TORAY PLASTICS | TORAY

Bear in mind that is one particular nylon formulation. The general trends it shows are what I’ve seen among many different nylon flavors, BUT the actual values can vary wildly with flavor.

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#9

I wonder… how well would a part printed with TPU work? I’m thinking something like: https://www.amazon.com/HATCHBOX-Printer-Filament-Dimensional-Accuracy/dp/B07P1BDCH6

I literally just got a spool of that stuff to play with, so I don’t have any experience with it just yet.

#10

and now i do (a little). Still playing with the print settings, but I printed a simple test piece - 1x.5x.125 inch box with 15% infill. I can fold it in half without any lasting impact or breakage. So, not quite what you’re looking for with the other materials, but certainly quite different properties!

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#11

For the last couple years we’ve printed our RSL mount out of TPU. Hasn’t broken off.

#12

Thanks! I do have some other filaments on hand I could test, including Dremel PET-G and Tiertime “Tough ABS.” Perhaps I can run at least one other material along with the “conditioned” Nylon samples.

In any case, I’m open to testing (sanitized) samples if folks want to send them to me. I’m due to receive FormLabs SLA-printed samples from a friend in the near future. This might be a stretch, but if folks want to buy me a roll in exchange for testing I wouldn’t be opposed to that either. :sweat_smile:

All samples were printed solid with .2 mm layer height. The “Printed Flat” and “Printed Standing” layouts were as follows (although printed seperately):

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All prints with the Dremel 3D45 were done with the online “Print Cloud” slicer on the glass bed w/ glue stick.

Both PLA+ grades were printed with the default Dremel settings: 220 C extruder temp, 45 C bed temp, 40 mm/s print speed.

The Nylon samples were printed at 255 C extruder temp, 90 C bed temp, 30 mm/s print speed. The standing Nylon samples were printed with a brim and reduced travel speed (130 mm/s down to 80 mm/s) since I was having issues with the extruder moving the parts off the bed towards the end of print.

If I’m remembering right, Onyx is printed at 275 C and speed is not actually exposed or configurable. Since the Onyx One and 3D45 have different hotends/nozzle materials, it’s difficult to exactly compare the actual temperatures experienced by the filaments during extrusion.

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#13

If you really want to go down a rabbit hole on improving part strength…

I really enjoy watching this guy’s experiments

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#14

You need to dry Nylon to properly print it but to get to its full strength you need to rehydrate it during which process it will “swell” between 0.5 to about 1 % in volume. To rehydrate you can either let it sit in the open for about 1 week or wrap it in a wet towel for about 24-48 hours. Some boil it for 10-15 min which will temporarily increase its strength but also mask potential defects which will become aparent when it reaches its equilibrium in about a week. Now this is not just a FDM thing but also holds true with injection molded Nylon. You can make a toughbox mini Nylon cover brittle by drying it as you described above. So if you do Nylon or its alloys dry - print - rehydrate

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