Standard Test Method for Tensile Properties of Single Textile Fiber - PDF

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ASTM D3822/D3822M measures the tensile properties of single textile fibers: breaking force, elongation at break, tenacity and initial modulus. It covers natural and man-made staple and filament fibers such as cotton, wool, polyester, nylon, aramid, carbon and glass. Because a single fiber breaks at only a few grams of force, the test needs a very low-capacity load cell and a careful mounting method.

What D3822 Measures

• Breaking force: peak force, in cN or gf

• Elongation at break: extension at break as a percentage of the gauge length

• Breaking tenacity: breaking force divided by the fiber's linear density, in cN/tex or gf/den

• Initial modulus: the slope of the first straight part of the force-elongation curve, also expressed per unit linear density

Tenacity is used instead of stress in MPa because fiber cross-sections are irregular and hard to measure; linear density (tex or denier) is easy to measure and is how fibers are bought and sold.

Specimen Preparation

• Mount each fiber on a paper or card tab frame with adhesive so it can be clamped without being crushed; cut the sides of the frame after it is in the grips

• Common gauge lengths are 10 mm, 20 mm and 25.4 mm (1 in); report the gauge length used

• Measure linear density of each fiber (for example with a vibroscope, ASTM D1577) or use the lot average

• Condition in the standard textile atmosphere of 21 ± 2 °C and 65 ± 5% RH (ASTM D1776)

• Test enough fibers for a stable average; fiber results scatter more than yarn or fabric results

Test Procedure

• Load the framed fiber in the grips, cut the frame sides and zero the force

• Pull at a constant rate of extension chosen from the fiber's expected elongation, as set out in the standard

• Record force and extension to break

• Discard fibers that break at the grip or slip in the adhesive

Calculations

Tenacity = breaking force ÷ linear density (cN/tex or gf/den)

Elongation at break (%) = extension at break ÷ gauge length × 100

Example: a 1.5 dtex (0.15 tex) polyester fiber breaks at 8.4 cN with 6.0 mm of extension on a 20 mm gauge. Tenacity = 8.4 ÷ 0.15 = 56 cN/tex (about 6.3 gf/den). Elongation = 6.0 ÷ 20 × 100 = 30%.

1 gf/den = 8.83 cN/tex.

Equipment

• Universal testing machine with a low-capacity load cell (2–10 N) and fine force resolution

• Light vise grips or pneumatic grips with rubber or paper-faced jaws so the fiber is not cut

• Tab frames and adhesive for mounting

• video extensometer if strain must be measured without contact

• Vibroscope or microbalance for linear density

Related Standards

• ASTM D2256 – tensile properties of yarns (single strand)

• ASTM D1577 – linear density of textile fibers

• ASTM D1776 – conditioning textiles for testing

• ISO 5079 – textile fibers, breaking force and elongation of individual fibers

• ASTM C1557 – tensile strength of single ceramic and carbon fibers

ASTM D3822 FAQ

What is fiber tenacity?

The breaking force divided by the fiber's linear density, reported in cN/tex or gf/den. It is the fiber equivalent of tensile strength and does not need a cross-sectional area.

What gauge length does ASTM D3822 use?

Common gauge lengths are 10 mm, 20 mm and 25.4 mm (1 in). The gauge length must be reported, because it affects the measured strength.

How are single fibers gripped?

Each fiber is glued across a paper or card tab frame. The frame is clamped in the grips and its sides are cut before testing, so the fiber is not crushed or damaged by the jaws.

How do I convert gf/den to cN/tex?

Multiply by 8.83. For example, 6.3 gf/den is about 56 cN/tex.