To determine the breaking strength, elongation, etc. of threads, yarns, or other single strand textiles, ASTM D2256 is by far the most common specification that is followed. This is a relatively simple tensile test whereby thread is pulled at a constant rate of speed until it breaks. Please see the video below that shows how the test is performed:
1. Load thread into pneumatic or manual rope grips
2. Gage length (length of thread between grips) should be 10″
3. One grip should pull the thread at a servo controlled constant rate of 12″ per minute.
Common measurements obtained:
1. Breaking Force (Maximum force)
2. Breaking Tenacity
B=F/T
B = Breaking Tenacity
F = Breaking Force
T = Linear Density in units of tex or denier
3. Elongation
4. Initial Modulus
5. Chord Modulus (Suggested elongation are 0% and 10%)
6. Breaking Toughness (Energy)
Tensile testing machine requirements:
1. Servo controlled constant rate of extension (CRE) tensile testing machine (if you have an ADMET machine, don’t worry, all ADMET machines are servo controlled and can do CRE testing)
2. Pneumatic or manual rope grips where the thread is wrapped around a mandrel (circular feature) or a “horn” shape and is then pinched in the grips. This prevents premature thread breakage.
3. Software that can automatically calculate all measurements (we use our MTESTQuattro software).
Tips:
1. Make sure your data acquisition is set high because the test is short as thread breakage happens quickly. We set our machines to 1,000 Hz to take 1,000 load and position measurements every second.
2. Make sure your thread is lined up evenly between the top and bottom grip. Slight errors in alignment can significantly alter the repeatability. By design, our “V” shaped channel pneumatic grips prevent misalignment.
