Single yarn breaking strength testing measures the maximum tensile force an individual yarn can withstand before rupture, together with its elongation at break, making it one of the most fundamental quality indicators in textile production. The test is performed on constant rate of extension (CRE) tensile testing machines in accordance with internationally recognized standards such as ISO 2062, ASTM D2256, and GB/T 3916. This article explains the test principles, sample requirements, procedures, calculations, and practical applications of single-end yarn tensile testing for spinning mills, fabric manufacturers, and accredited third-party laboratories.
Technical Overview
The breaking strength of a single yarn, formally referred to as single-end breaking force, is the maximum force recorded when an individual yarn specimen is stretched to rupture on a tensile testing machine under specified conditions. During the same test, the corresponding elongation at break—the percentage increase in length at the moment of maximum force—is also captured, and derived values such as tenacity (force per unit linear density) can be calculated.
Single yarn tensile properties are among the most decisive quality parameters in the textile value chain. Yarn strength directly determines warping and weaving efficiency, the frequency of yarn breakage during high-speed knitting, the tensile performance of the finished fabric, and the durability of the final garment or technical product. A weak or irregular yarn causes machine stoppages, fabric defects, and downstream claims, which is why spinning mills, weaving plants, and buyers routinely verify single yarn breaking force before accepting or releasing material.
Modern testing is performed almost exclusively on CRE (constant rate of extension) instruments, which stretch the specimen at a constant rate while continuously recording the force-elongation curve. The results are statistically processed to report the mean breaking force, mean elongation at break, and their coefficients of variation, providing a complete picture of both strength and strength uniformity.
Testing Samples
Spun Yarns from Natural Fibers
Cotton (carded and combed), wool (worsted and woolen), linen, silk, and other natural fiber yarns supplied on bobbins, cones, or tubes. Linear densities typically range from coarse counts for denim to fine counts for shirting and lingerie fabrics.
Filament and Synthetic Yarns
Polyester, nylon, polypropylene, viscose rayon, acetate, and acrylic yarns in filament form, including partially oriented (POY), fully drawn (FDY), and draw-textured (DTY) variants, as well as industrial filament yarns used in technical applications.
Blended and Specialty Yarns
Polyester-cotton and other blended spun yarns, core-spun yarns with elastane or filament cores, air-jet and friction-textured yarns, sewing threads, embroidery yarns, and reinforcing yarns for composites and tire cords.
Sample Preparation and Conditioning
- Yarn must be taken from undamaged packages, and the first several meters from each package should be discarded to avoid degraded surface layers.
- Prior to testing, specimens are conditioned in the standard atmosphere for textile testing—typically 20 ± 2 °C and 65 ± 4 % relative humidity—until moisture equilibrium is reached, normally a minimum of 24 hours.
- A representative sampling plan is required: unless otherwise agreed, specimens are drawn from multiple packages across the production lot so that the test results reflect lot-level variability.
- Linear density (tex) of each yarn lot should be known or determined, since tenacity calculations depend on it.
Testing Items
The following parameters are obtained or derived from a single yarn breaking strength test:
- Breaking force (single-end breaking strength), expressed in newtons (N) or centinewtons (cN)—the maximum force sustained by the yarn before rupture.
- Elongation at break (%), the extension of the specimen at maximum force relative to the initial gauge length.
- Tenacity (cN/tex), calculated as the breaking force divided by the linear density; in trade practice this is often expressed as breaking length in kilometers (RKM).
- Coefficient of variation (CV%) of breaking force and elongation, reflecting yarn evenness and strength uniformity across and within packages.
- Work to break (breaking toughness), the area under the force-elongation curve, indicating the energy absorbed before rupture where the testing machine software provides this output.
- Force-elongation curve characteristics, such as initial modulus and yield behavior, useful for fiber identification and process analysis.
Testing Methods
ISO 2062 — Yarns from Packages
ISO 2062 specifies the determination of single-end breaking force and elongation at break using a CRE tester. It prescribes a gauge length of 500 mm (250 mm where package size is limited), a pre-tension of 0.5 cN/tex for most yarn types, and an extension rate selected so that the average time to break falls within approximately 20 ± 3 seconds, with a default speed of 500 mm/min for many applications.
ASTM D2256 — Single-Strand Method
ASTM D2256 covers tensile properties of yarns by the single-strand procedure on CRE equipment. It uses a nominal gauge length of 250 mm (10 in.), a crosshead speed adjusted to achieve break within the specified time window, and pre-tension values defined according to yarn type and linear density. Force and extension data are reported along with statistical summaries.
GB/T 3916 — Chinese National Standard
GB/T 3916 is the Chinese national standard for determining single-end breaking force and elongation at break of yarns from packages. It is technically aligned with ISO 2062 and is the reference method commonly specified in Chinese domestic trade contracts and mill quality specifications.
Equipment and Test Procedure
- A CRE-type electronic tensile tester with a load cell whose capacity is matched to the expected breaking force (typically within 10–90 % of capacity) is used, equipped with pneumatic or mechanical clamps and suitable jaw liners to prevent slippage without jaw damage.
- The specimen is clamped at the specified gauge length, the specified pre-tension is applied, and the lower jaw extends the specimen at the prescribed rate until rupture.
- Breaks that occur within approximately 5 mm of the jaw line, or specimens that slip in the clamps, are rejected and retested, as such results underestimate true yarn strength.
- A minimum of 20 valid breaks (for example, several specimens from each of several packages) is normally tested unless the product specification or contract states otherwise.
- The instrument records maximum force and elongation at maximum force for each specimen and computes the arithmetic mean, CV%, and, where linear density is entered, tenacity.
Calculation and Expression of Results
The mean breaking force is reported in N or cN, mean elongation at break in %, and tenacity in cN/tex, each accompanied by the coefficient of variation. Tenacity is obtained by dividing the breaking force by the yarn linear density, which allows objective comparison between yarns of different counts. Results should identify the standard applied, the number of specimens, gauge length, testing speed, pre-tension, and the conditioning atmosphere, ensuring full traceability and reproducibility of the test report.
Applications
- Spinning mill quality control: monitoring strength and CV% across shifts and machines, optimizing twist levels, and validating spinning process settings.
- Weaving and knitting readiness: confirming that warp and weft yarns meet minimum strength thresholds required for high-speed processing and acceptable loom efficiency.
- Incoming inspection: fabric mills, garment manufacturers, and brand purchasers verifying supplier declarations against contractual strength specifications.
- Product development: comparing fiber blends, yarn structures, and finishing treatments during new product design and benchmarking.
- Technical and industrial textiles: qualifying sewing threads, reinforcement yarns, tire cords, and geotextile yarns against demanding strength requirements.
- Trade and certification: accredited third-party laboratories issue test reports based on ISO 2062, ASTM D2256, or GB/T 3916 for customs clearance, arbitration, and compliance with purchase agreements.
FAQ
What pre-tension is applied during the test?
Under ISO 2062, a pre-tension of 0.5 cN/tex is applied to most yarn types to remove crimp and establish a defined starting length; the standard provides alternative values for specific materials. ASTM D2256 defines pre-tension based on yarn type and linear density. Using the correct pre-tension is essential because it directly affects the measured elongation at break.
Why must a CRE machine be used?
Constant rate of extension instruments stretch the specimen at a uniform, controlled rate, giving well-defined force-elongation curves and superior inter-laboratory reproducibility. Older CRT (constant rate of traverse) pendulum-type testers are obsolete and their results are not comparable with CRE results, so modern standards specify CRE exclusively.
How many specimens should be tested?
A minimum of 20 valid breaks is the common requirement, taken from multiple packages to capture both within-package and between-package variation. Product specifications or commercial agreements may require more, such as 10 packages with several tests each, to tighten confidence in the reported mean.
Why are jaw breaks discarded?
When a specimen fails immediately at the clamp line, the rupture is caused partly by stress concentration or jaw damage rather than pure tensile failure, producing an artificially low result. Such breaks, along with specimens that slip in the jaws, are rejected and additional specimens are tested.
How is tenacity different from breaking force?
Breaking force is the absolute maximum load the yarn withstands, which depends on how coarse the yarn is. Tenacity divides that force by the linear density (cN/tex), normalizing for yarn count so that fine and coarse yarns can be compared on equal terms—one RKM corresponds numerically to one cN/tex.
Why is conditioning necessary before testing?
Yarn strength and elongation are sensitive to moisture content and temperature. Conditioning all specimens in the standard atmosphere ensures equilibrium and makes results comparable between laboratories and over time, particularly for hygroscopic fibers such as cotton, viscose, and wool.