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Filament tensile strength

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WhatUPSbox?:
On page 2 of Bob's great Tensile strength testing thread (https://www.gatewaytoairguns.org/GTA/index.php?topic=210856.20) he showed a large difference between name brand and econo PLA. That got me wondering how much the strength of the basic filament varies.
My mini-lathe is probably too small to duplicate Bob's set-up, but I have some mechanical parts that could be set up for similar function. The first image shows the overall configuration. A small 3 rpm D.C. gear motor drives a leadscrew that then pulls on the moving block side. The fixed side is attached to a load cell (300 Kg) processed by an Arduino.
The second image shows the filament in place. The aluminum cylinders have a groove for the filament and I use some additional foam to try to reduce local loading. During test, all the connections are left relatively loose to allow some self alignment under tension. The gear motor and leadscrew result in about a 1 inch/min pull rate. I tested the rig to 50 Kg, the typical pull is around 12 Kg. I don't know what the brass leadscrew nut can take.
Some results from the checkout tests are shown. I think most of the filaments would be considered Amazon sourced econo. Some of the PLA is quite old, different levels of dryness etc.
Already have a list of test process improvements. I also need to try larger diameter cylinders. I think the stiff PLA had some bending moment added at the tangent point. But overall I'm happy with the process.

rsterne:
Looks like a good setup for testing the strand of filament.... A lot less variables will help your data for sure!....

Bob

WhatUPSbox?:
My thinking is that the filament strength should be the upper bound for a print with that filament. It may be worth monitoring as the filament ages.

During checkout I was using tennis string (mostly nylon). It is 1.3mm diameter (.0021 in2), I normally string at 55 lbs (26,190 psi) and found a reference quoting 129 lbs ultimate (61,429 psi). Almost an order of magnitude stronger than the filaments I was testing. Would be expensive stuff to print with but you've got to like the numbers.

rsterne:
Interesting, considering that the ultimate tensile strength of 6061-T6 aluminum is 45,000 psi.... I looked up high tensile strength plastics and got the following....


--- Quote ---Top 4 High Tensile Strength Plastics

    PAI – Polyamideimide (PAI) boasts the highest tensile strength of any plastic at 21,000 psi. This high performance plastic has the highest strength of any unreinforced thermoplastic, good wear and radiation resistance, inherently low flammability and smoke emission, and high thermal stability. PAI parts can be found in engines, valves, gears, electrical connectors, and thrust washers.
    Ultem® – Also known as PEI, Ultem® has a tensile strength of 15,200 psi and an excellent combination of mechanical properties. It is easily machined and fabricated, has excellent strength and rigidity, a high dielectric strength, and a continuous use temperature of 340ºF. PEI is often used in medical and chemical instrumentation due to its heat, solvent, and flame resistance.
    PEEK – One of the best high performance engineering thermoplastics on the market, PEEK has a superior mix of mechanical properties, including a tensile strength of 14,000 psi. It can withstand high temperatures (up to 480ºF for continuous use), has inherently good wear and abrasion resistance, and offers excellent chemical and hydrolysis resistance. PEEK can be found in the most demanding applications and harshest environments, such as aircraft parts, bearings, pumps, and medical implants.
    Nylon – An honorable mention goes to Nylon, with a tensile strength of 12,400 psi. This high tensile strength plastic can often be overlooked, but it has a relatively high melting point (450ºF) and exhibits excellent abrasion resistance. It also has high chemical resistance and is not damaged by oils, solvents or alcohols. Nylon is used in a wide array of applications, from compound bow strings to substituting for low strength metals.

--- End quote ---

I got just over 13,000 psi for Carbon Fibre reinforced PA612 Nylon in my recent testing....

Bob

WhatUPSbox?:
I was surprised when a 1.25mm line didn't break during my proof test. Here is a reference for tennis string.
https://racquetquest.tennis/category/tensile-strength/
I also looked up fishing line and you also get high tensile strength capability for monofilament nylon line.
https://tacklevillage.com/fishing-line-strength-chart/

Not sure about the discrepancy with printer filament. While some tennis strings have Kevlar in them, those have even higher numbers.

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