Just How Strong is PLA? Lab Experiment!

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Just How Strong is PLA? Lab Experiment!
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So I had the wonderful opportunity to use my school’s physics lab for whatever experiment I wanted, as long as the teacher approved and as long as it was for the purpose of a school paper. So, I decided to test how much stress could be tolerated by 3D Printed PLA bars, with different settings (layer height, wall thickness and infill to be exact).

However, the results I found were not repeatable enough or conclusive enough for me to write a school paper and lab report with, but that means that I am free to publish my results!

So here goes.

I 3D Printed 4 sets of 3 bars each. Those had the following differences:

• 0.100 layer height, 30% infill, 0.4 wall thickness (0.100/30/0.4)
• 0.100 layer height, 100% infill, 0.4 wall thickness (0.100/100/0.4)
• 0.100 layer height, 30% infill, 1.2 wall thickness (0.100/30/1.2)
• 0.300 layer height, 30% infill, 1.2 wall thickness (0.300/30/0.4)

All the bars had dimensions (within an error boundary of 1mm) are 239mm x 5.5mm x 5.5mm. They were printed with green PLA, at 215oC.

The first setup I tried was to place the bar between two metal bars, place weights in the middle of the bar, and see under what weight they would break.

Below is a photo of one of the tests.

test1 - PLA
The initial setup

To my surprise, the bars were very, very, very elastic and equally strong. The weakest 0.300/30/0.4 bar withstood a total of 978 grams, really close to a full kilogram. A full kilogram and that was the weakest bar!

Testing the rest of the bars was a bit of a pain, because they would bend so much that they would simply slip from their position and fly across the room. Unfortunately, no video footage survives from that day.

I acknowledge that material stress and continuous stress played a significant role to the results, but that was a problem I had to accept with this experimental setup.

The way I compared their strength next was that I, in few words, Chinese-tortured them. I placed each bar to stand between two metal pieces, tied the middle of it with a string, and made the string pass through a pulley to a rotating wheel, that draws the string inwards.

Now, I could also connect the string to a Newton-counter, and record exactly what force the bar experiences.

setup2 - PLA
The 2nd experimental setup.

And yeah…

I did indeed got some funky data, to say the least. Here is a snapshot and the resulting table from the Force recording program, draw your own conclusions. It is vividly evident that the bars do indeed handle prolonged stresses differently, and do take a toll on the total strain the bars can handle.

pasco - PLA
The data for Trial 1 of the third bar type.
                Trial 1                                        Trial 2                  Trial 3

0.100/30/0.4    10.76N (Not enough string)                     10.86N (Break)           21.0N
0.100/30/1.2    22.0N (Slip, last run before setup change)     -                        -
0.100/100/0.4   20.2N (Slip)                                   21.5N (string snapped)   -
0.300/30/0.4    20.7N (Break)                                  18.9N (Break)            -

Even if I have some numbers at hand, most of the bars still either slipped or could not reach their potential maximum breaking point. Still, the data supports that these bars can withstand a minimum of 2 kilograms of weight. 2 Kilograms on a 5mm*5mm plastic bar! I could not believe it!

But wait, there’s more!

I tried a third technique, where I secured in place both the ends of the plastic bar, and stressed the middle of the bar, where it could not move freely. And despite all expectation, we maxed out the instrument limit of 50N, 5 kg!, and the bar was fine afterwards (I do not remember which bar that was). I have no photo of that available, as I only did 1 test and decided to change the topic of my project entirely.

So, in conclusion, PLA bars are extremely tough and elastic considering they are plastic. One tiny bar can easily hold 1 kilogram of weight, and go up to 5 and even more! Perhaps PLA could be used more to create objects to withstand pressures and loads, as is the big dream of making and 3D Printing.

Note to physicists, engineers, etc: I finally tried to measure the Young’s modulus of elasticity for those PLA bars, but because I could only print small bars no more than 35cm in length, I could not get any good, repeatable, or steady readings, and the results I did get were everything but comprehensible.

3 Comments
  1. [email protected] says

    Thanks for taking the time and doing this. It is something we should know about.

  2. cody foreman says

    awesome

  3. jvastine says

    Nice! A good follow up would be how PLA compares to other material
    Peace!

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