All Springer/NP/PCP Air Gun Discussion General > 3D printing and files

Filament tensile strength

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Bob, you probably saw this CNC  Kitchen video on printing with weedwacker string. Note that he allowed the coupons to reabsorb moisture before testing.

I don't know how the tennis strings stand that much loading.... It must have something to do with how they yield under load, I guess.... A polymer scientist I'm not!....


I'm not one either.
Just out of curiosity, I took a look at the broken ends of the filaments. The PETG all had that neck down and mushroom on both sides of the break. The PLA did not but it lightened in the stressed area (the PLA sample is nominally black).
No idea what it means if anything.

I don't know what causes the "mushroom", but my guess is that it is the stretched material "snapping back" after failure.... The lightening in colour on the PVA is likely "crazing", which is microcracks forming under stretch just before fracture.... I see the same thing on some of my horizontal (XY) tensile coupons when the stretch before or after the yield point....


I added some lever arms to my test rig to allow coupon level loads. Using Bob's coupon files, the checkout pull (generic silver PLA) provided reasonable Z axis data (3,344 psi). I don't intend to duplicate Bob's great work, I'm curious to see if there is a link between filament strength and printed coupon strength, especially XY.


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