Breaking strength testing standards define the standardized laboratory procedures used to measure the maximum tensile force a material can withstand before rupture, delivering critical quality and safety data for fabrics, nonwovens, coated textiles, webbing, and technical yarns. This comprehensive guide explains the governing standards published by ISO, ASTM, EN, GB, and JIS, and covers sample requirements, key test items, strip and grab test methodologies, data processing rules, and typical industrial applications.
Technical Overview
Breaking strength, also referred to as breaking force, is the maximum tensile force sustained by a specimen when it is stretched to rupture in a controlled tensile testing machine, expressed in newtons (N). It is one of the most fundamental mechanical indicators for textile and flexible materials, directly reflecting durability, structural integrity, and suitability for the intended end use. Because the result depends heavily on specimen geometry, clamping conditions, extension rate, and atmospheric conditioning, a family of international standards has been established to harmonize testing across laboratories and markets.
The principal standards governing breaking strength determination include:
- ISO 13934-1 / EN ISO 13934-1 — Textile fabrics, determination of tensile properties, strip method
- ISO 13934-2 / EN ISO 13934-2 — Textile fabrics, determination of tensile properties, grab method
- ASTM D5035 — Breaking force and elongation of textile fabrics, strip method
- ASTM D5034 — Breaking strength and elongation of textile fabrics, grab test
- GB/T 3923.1 and GB/T 3923.2 — Chinese national standards, technically aligned with ISO 13934-1 and ISO 13934-2
- JIS L 1096 — Japanese standard covering strip and grab tensile testing of woven and knitted fabrics
- ISO 13935-1, ISO 13935-2 and ASTM D1683 — seam breaking strength by strip and grab procedures
- ISO 9073-3, ASTM D5032 and ASTM D5733 — breaking force of nonwoven materials by strip and grab methods
- ISO 1421 and ASTM D751 — tensile strength of rubber- or plastic-coated fabrics
- ASTM D6775 — tensile properties of textile webbing, tape, and braided materials
- ISO 10319 and ASTM D4595 — wide-width tensile testing of geotextiles
- ISO 2062 and ASTM D2256 — tensile properties of single yarns and threads
All modern procedures are based on the constant rate of extension (CRE) principle, in which the moving clamp travels at a fixed speed while the force transducer records the load–extension curve until rupture. Instruments must be verified and calibrated in accordance with force-verification standards such as ISO 7500-1 or ASTM E4, with measurement accuracy typically within ±1% of the indicated force. Before testing, specimens are conditioned in a standard atmosphere as defined in ISO 139 or ASTM D1776, normally 20 ± 2 °C and 65 ± 4% relative humidity, until moisture equilibrium is reached.
Testing Samples
Breaking strength determinations are applied to a broad range of flexible materials. The applicable standard and specimen geometry depend on the product category, as summarized below.
Woven Fabrics
Woven apparel and industrial fabrics are the most common test subjects. Specimens are cut in both the warp (lengthwise) and weft (crosswise) directions, usually at least five per direction, taken at evenly spaced positions across the fabric width and away from selvedges and roll ends. Strip specimens are typically cut at 60 mm width and raveled to a 50 mm effective width, while grab specimens are prepared at approximately 100 mm width.
Knitted Fabrics
Because knitted structures are prone to distortion and curling during cutting, the grab method is generally preferred for knits. Highly elastic knitted fabrics containing elastane may require dedicated procedures for tension and elongation, such as ASTM D4964, since conventional breaking force measurements can be dominated by excessive elongation rather than true rupture strength.
Nonwoven Fabrics
Spunbond, meltblown, needle-punched, and hydroentangled nonwovens are tested in machine and cross-machine directions using ISO 9073-3 or the ASTM strip and grab methods for nonwovens. Specimen widths and gauge lengths follow procedures similar to those used for wovens, with sampling distributed across the full web width to account for machine-direction anisotropy.
Coated and Laminated Fabrics
Fabrics coated with PVC, PU, or rubber, as well as laminated multilayer composites used for tarpaulins, inflatable products, and protective clothing, are tested according to ISO 1421 or ASTM D751. Specimen preparation must avoid damaging the coating layer, and delamination during extension is recorded as an observation because it affects the interpretation of the breaking force.
Webbing, Tapes, and Narrow Fabrics
Safety harness webbing, lifting sling webbing, seat belts, straps, and hook-and-loop tapes are tested full width at their as-produced configuration under ASTM D6775. Testing narrow fabrics in their finished form, including any stitching or coating, ensures the result reflects real-world performance in load-bearing applications.
Geotextiles and Technical Textiles
Geotextiles, geogrids, and other reinforcement textiles are evaluated by wide-width tensile testing under ISO 10319 or ASTM D4595, typically using 200 mm wide specimens. The wide-width configuration reduces the jaw effects and edge effects that would otherwise distort results for high-strength, low-elongation materials used in civil engineering.
Yarns and Sewing Threads
Single yarns, industrial filaments, and sewing threads are tested on CRE single-strand tensile testers per ISO 2062 or ASTM D2256. In addition to breaking force in N or cN, results are normalized to linear density to yield tenacity in cN/tex, allowing comparison between yarns of different counts.
Testing Items
A breaking strength test program typically reports the following measured and derived quantities:
- Breaking force (maximum force at rupture), expressed in N or cN
- Breaking strength per unit width, expressed as N/50 mm (commonly written N/5 cm in specifications)
- Elongation at break, expressed as a percentage of the initial gauge length
- Elongation at maximum force, for materials that exhibit force peaks before final rupture
- Seam breaking strength, measured on seamed specimens per ISO 13935-1, ISO 13935-2, or ASTM D1683
- Seam slippage resistance, evaluated under ISO 13936 series or ASTM D434
- Yarn tenacity and breaking tenacity in cN/tex per ISO 2062 or ASTM D2256
- Initial modulus and force at specified elongation, when required by technical specifications
For acceptance purposes, the arithmetic mean of valid replicate specimens is compared against the minimum requirement stated in product standards or purchase contracts. Coefficients of variation are also frequently reported, as excessive scatter may indicate non-uniform material quality or sampling problems.
Testing Methods
Specimen Preparation and Conditioning
Samples are taken from representative production lots, avoiding selvedges, roll ends, creases, and visibly defective areas. Specimens in each direction are cut parallel to the yarns being tested and spaced apart so that no two specimens contain the same lengthwise yarns. All specimens are conditioned in the standard atmosphere of 20 ± 2 °C and 65 ± 4% relative humidity for a minimum of 24 hours, or until moisture equilibrium is achieved, before clamping.
Strip Method (ISO 13934-1, ASTM D5035, GB/T 3923.1)
The strip method measures the force required to break a specimen of defined effective width. Under ISO 13934-1, a raveled strip with a 50 mm effective width is tested at a 200 mm gauge length with a small pretension applied according to fabric mass per unit area. The extension rate is selected based on the expected elongation at break: approximately 20 mm/min for fabrics elongating 8% or less, 100 mm/min for elongation between 8% and 75%, and 200 mm/min for highly extensible fabrics. ASTM D5035 uses a narrower cut strip, typically 25 mm or 50 mm wide, with a shorter gauge length and a standard rate of 300 mm/min. Because the entire specimen cross-section is stressed, the strip method provides the most reproducible measure of intrinsic fabric tensile performance.
Grab Method (ISO 13934-2, ASTM D5034, GB/T 3923.2)
In the grab method, only the central portion of the specimen width is gripped by the jaws, typically clamping an effective width of about 25 mm while the specimen itself is approximately 100 mm wide. Gauge lengths are typically 100 mm under ISO 13934-2 at an extension rate of 50 mm/min, and 75 mm under ASTM D5034 at 300 mm/min. The grab method is faster, requires less specimen preparation, and better reflects the behavior of fabrics stressed at a localized point, making it suitable for routine quality control and for knitted or loosely constructed fabrics.
Wide-Width Method for Geotextiles (ISO 10319, ASTM D4595)
Geotextile specimens of 200 mm width are extended at rates selected according to the material's elongation characteristics, using reinforced clamp faces and often specimen tabs to prevent slippage of high-strength polymer grids and fabrics. Results are reported as maximum tensile force in kN/m together with elongation at maximum force.
Narrow Fabric Method (ASTM D6775)
Webbing and tapes are tested at full as-produced width, commonly using gauge lengths in the range of 100 to 250 mm and extension rates up to 300 mm/min. Breaking force, elongation at specified forces, and the load–extension curve shape are recorded, which is essential for evaluating energy absorption in safety-critical webbing.
Data Processing and Reporting
For each direction, at least five valid replicates are obtained. Specimens that slip in the jaws, break within approximately 5 mm of the jaw face, or fail outside the gauge region are normally discarded and replaced, since such failures underestimate true material strength. The reported breaking strength is the arithmetic mean of valid results, accompanied by the coefficient of variation and individual values where required. Test reports must identify the standard used, the method variant, machine type, conditioning atmosphere, specimen dimensions, and any observed anomalies such as jaw breaks or coating delamination.
Applications
Breaking strength test data support quality control, product certification, and research across many industries:
- Apparel and home textiles — verifying that shirting, suiting, denim, upholstery, and bedding fabrics meet minimum warp and weft breaking force requirements in product standards and buyer specifications
- Personal protective equipment — qualifying webbing and textile components of safety harnesses, fall-arrest systems, and protective garments where tensile integrity is safety-critical
- Automotive and transportation — evaluating seat belt webbing, airbag fabrics, seat coverings, and interior trim textiles against OEM performance specifications
- Medical textiles — confirming the strength of wound dressings, surgical gowns, disposable nonwovens, and pressure garments
- Construction and civil engineering — determining the wide-width tensile strength of geotextiles used in soil reinforcement, separation, and filtration
- Packaging and industrial products — validating coated fabrics, tarpaulins, flexible intermediate bulk container fabrics, lifting slings, and cargo straps
- Military, aerospace, and outdoor equipment — qualifying parachutes, tents, ropes, climbing gear textiles, and ballistic fabric substrates
Manufacturers, brand owners, and regulators rely on accredited third-party laboratories to perform these tests under the applicable ISO, ASTM, EN, GB, or JIS procedures, ensuring that reported breaking strength values are traceable, comparable, and defensible in international trade and certification contexts.
FAQ
What is the difference between the strip method and the grab method?
The strip method grips the full effective width of the specimen (typically 50 mm under ISO or 25–50 mm under ASTM), so the entire cross-section carries the load and the result represents intrinsic yarn and fabric strength. The grab method grips only the central portion of a wider specimen, simulating localized stress and requiring minimal preparation. Strip results are usually lower than or equal to grab results for the same fabric, and the two methods are not interchangeable without an established correlation.
Are ISO 13934 and ASTM D5034/D5035 results directly comparable?
No. The standards differ in specimen width, gauge length, extension rate, and pretension. For example, ISO 13934-1 uses a 50 mm raveled strip at a 200 mm gauge length with speed selected by elongation class, while ASTM D5035 typically uses a 25 or 50 mm cut strip at a shorter gauge and 300 mm/min. Results should only be compared when the same standard and parameters are used, and contracts should always specify the exact method.
How many specimens are required for a valid breaking strength test?
Most fabric standards require at least five valid specimens in each principal direction (warp and weft, or machine and cross-machine), with specimens distributed across the material width so they do not share the same yarns. If a specimen slips in the jaws or breaks at the jaw line, it is replaced with an additional specimen so that the reported mean is based on the required number of valid failures.
What is the difference between breaking force and tensile strength?
Breaking force is the maximum applied load expressed in force units such as newtons, and it is the standard reporting quantity for fabrics, webbing, and yarns. Tensile strength, in the strict materials-science sense, refers to stress (force per unit original cross-sectional area, such as MPa) and is mainly used for homogeneous engineering materials. For textiles, breaking force or breaking strength per unit width (N/50 mm) is the conventional expression.
What acceptance criteria are typically specified for breaking strength?
Acceptance limits depend entirely on the end use and the governing product standard or purchase contract. Lightweight apparel fabrics may be specified at minimum forces in the range of a few hundred newtons, whereas industrial webbing for safety harnesses or lifting slings must demonstrate breaking forces of many kilonewtons. Test reports should therefore always be evaluated against the specific minimum requirements of the applicable product standard or client specification.
Why is conditioning necessary before testing?
Moisture content significantly affects the mechanical behavior of hygroscopic fibers such as cotton, viscose, and wool. Conditioning specimens to equilibrium at 20 ± 2 °C and 65 ± 4% relative humidity, as specified in ISO 139 or ASTM D1776, ensures that breaking strength results are reproducible between laboratories and comparable across different lots and test dates.
