Breaking strength evaluation standards define the standardized laboratory procedures used to determine the maximum tensile force a material can withstand before rupture. This technical guide explains the internationally recognized test methods published by ISO, ASTM, EN, GB and JIS, covering sample preparation, key test parameters, result calculation and typical industrial applications.
Technical Overview
Breaking strength, also referred to as breaking force or maximum force, is the greatest tensile load a specimen sustains immediately before rupture. It is one of the most fundamental mechanical indicators for textile fabrics, yarns, webbings and coated materials, expressed in newtons (N) or pound-force (lbf). Breaking strength evaluation standards establish a unified framework for specimen preparation, atmospheric conditioning, equipment requirements, testing speed and result calculation, ensuring that measured values are reproducible between laboratories and comparable across supply chains.
Modern breaking strength evaluation is performed on constant-rate-of-extension (CRE) universal tensile testing machines. Prior to testing, specimens are conditioned in the standard textile atmosphere defined in ISO 139, namely 20 ± 2 °C and 65 ± 4 % relative humidity, because moisture content significantly influences the tensile behavior of hygroscopic fibers such as cotton, viscose and wool.
The principal standards governing breaking strength evaluation include:
- ISO 13934-1 and ISO 13934-2 — tensile properties of fabrics by the strip method and the grab method, adopted in Europe as EN ISO 13934-1 and EN ISO 13934-2
- ASTM D5035 and ASTM D5034 — breaking force of textile fabrics by the strip method and the grab method
- GB/T 3923.1 and GB/T 3923.2 — Chinese national standards for fabric tensile testing, technically aligned with the ISO 13934 series
- ISO 13935-1, ISO 13935-2, ASTM D1683 and GB/T 13773 — seam tensile properties
- ISO 2062, ASTM D2256 and GB/T 3916 — single-end breaking force and elongation of yarns
- ASTM D6775 — breaking strength and elongation of textile webbing, tape and braided material
- ISO 10319 and GB/T 15788 — wide-width tensile testing of geotextiles
- JIS L 1096 — Japanese testing methods for woven and knitted fabrics, including tensile options
Testing Samples
Woven and Knitted Fabrics
Fabric samples are taken from laboratory swatches or production rolls at positions representative of the lot, cut well away from the selvedge and from roll ends. At least five specimens are prepared in each principal direction, with each specimen cut precisely parallel to the warp or weft yarns being tested so that the applied load is carried uniformly across the full specimen width.
Webbing, Tape and Braided Materials
Narrow fabrics such as safety webbing, lashing straps and braided cords are tested at their full manufactured width, since cutting or raveling these products would destroy their load-bearing structure. Specimens are taken from continuous lengths, free from visible defects, kinks or abrasion damage, and are tested with their as-supplied finish.
Yarns and Sewing Threads
Yarn specimens are drawn from conditioned packages with minimal tension to avoid altering twist. Multiple individual strands, commonly ten per package, are tested to characterize the single-end breaking force and elongation, and results are frequently normalized to tenacity in centinewtons per tex for comparison between yarn counts.
Seamed Specimens
For seam strength evaluation, fabric specimens are first joined using a documented stitch type, sewing thread and stitch density, then loaded in the same direction as the seam line. This configuration measures the force required to rupture the seam or the fabric adjacent to it, which is critical for garment durability assessment.
Testing Items
Depending on the product and the applicable specification, a breaking strength evaluation program typically covers the following measurable items:
- Maximum force (breaking force) sustained by the specimen, reported in N, kN or lbf
- Elongation at maximum force, expressed as a percentage of the initial gauge length
- Elongation at rupture (breaking elongation)
- Elongation at a specified force, used for applications with controlled stretch requirements
- Seam breaking force and seam efficiency, comparing seamed strength with unseamed fabric strength
- Single-end breaking force and tenacity for yarns and sewing threads
- Breaking strength retention after laundering, UV exposure, heat aging or chemical treatment, expressed as a percentage of the original value
- Statistical treatment of results, including arithmetic mean and coefficient of variation
Testing Methods
All major standards now specify constant-rate-of-extension (CRE) tensile testers equipped with calibrated load cells appropriate to the expected force range. The extension rate is selected so that specimen rupture occurs within the time window prescribed by each method, and force-elongation curves are recorded digitally for subsequent evaluation.
Strip Method
The strip method described in ISO 13934-1, ASTM D5035 and GB/T 3923.1 grips the full width of a 50 mm wide specimen between the jaws. With a gauge length of 200 mm under the ISO procedure, the extension rate is 20 mm/min for fabrics with elongation below 75 % and 100 mm/min for fabrics with higher elongation. Because every yarn across the specimen width carries load, the strip method yields the true uniaxial tensile strength of the fabric and is preferred for specification and certification purposes.
Grab Method
The grab method of ISO 13934-2, ASTM D5034 and GB/T 3923.2 uses a wider specimen in which only the central portion, typically 25 mm, is clamped by the jaws. Under ASTM D5034 the jaw separation is 75 mm and the crosshead speed is 300 mm/min. The grab method is faster, requires less specimen preparation and better reflects in-service conditions where load is transmitted through only part of the fabric width. It is particularly suitable for coated, high-density or difficult-to-ravel fabrics.
Single-End Yarn Method
ISO 2062, ASTM D2256 and GB/T 3916 determine the breaking force of individual yarns, commonly using a 500 mm gauge length with a standardized pre-tension of 0.5 cN/tex applied to remove crimp without stretching the yarn. The method outputs breaking force, elongation at break and tenacity, supporting yarn quality control and process optimization in spinning and sewing operations.
Narrow Fabric Method
ASTM D6775 addresses webbing, tape and braided material tested at full width on CRE equipment, with gauge length and operating speed set according to the standard. This method underpins quality control for lifting slings, cargo restraint webbing, harness components and military textile hardware.
Wide-Width Method for Geotextiles
ISO 10319 and GB/T 15788 evaluate geotextiles using wide strips, typically 200 mm wide with a 100 mm gauge length and an extension rate of 20 mm/min. The wider specimen reduces the influence of local fabric structure variability and provides the tensile parameters used directly in soil reinforcement design.
Data Treatment and Reporting
The reported breaking force is the mean of all valid determinations. Specimens that rupture within 5 mm of the jaw line are classified as jaw breaks: ISO practice requires such results to be recorded and additional specimens to be tested, while ASTM practice allows jaw breaks to be retained and flagged or discarded under documented agreement. A complete test report identifies the standard applied, machine type, conditioning atmosphere, specimen dimensions, individual and mean results, coefficient of variation, and any deviations from the standard.
Applications
Breaking strength evaluation according to recognized standards supports product development, specification compliance, factory quality control and independent verification by accredited third-party laboratories. Typical application areas include:
- Apparel and home textiles, where fabric and seam strength values are checked against buyer specifications and national product standards
- Industrial safety equipment, including webbing lifting slings tested under EN 1492-1 and EN 1492-2, lashing straps under EN 12195-2 and fall-arrest harnesses under EN 361, where breaking force must demonstrate the required safety factor above the working load limit
- Automotive textiles, such as safety-belt webbing, airbag fabrics and seat components, verified against OEM technical requirements
- Geosynthetics, where wide-width tensile data from ISO 10319 and GB/T 15788 feeds directly into reinforcement design calculations for roads, embankments and retaining structures
- Packaging and logistics, covering woven strapping, tie-downs and flexible intermediate bulk container fabrics
- Medical and technical textiles, including surgical textiles, filtration fabrics and coated protective materials
- Research and development, comparing fiber blends, weave structures, finishes and joining techniques on a common strength basis
FAQ
What is the difference between the strip method and the grab method?
The strip method grips the entire specimen width and measures the true uniaxial tensile strength of the fabric, whereas the grab method grips only the central portion of a wider specimen and reflects localized load transfer similar to real service conditions. Strip values are generally preferred for specifications, while grab values are commonly higher for many woven constructions and faster to obtain.
What units are used to report breaking strength?
Breaking force is reported in newtons (N) or kilonewtons (kN) in ISO, EN, GB and JIS systems, and may be reported in pound-force (lbf) under ASTM procedures, where 1 lbf is approximately 4.448 N.
Why must specimens be conditioned before testing?
Most textile fibers are hygroscopic, and their strength changes with moisture content. Conditioning all specimens in the standard atmosphere of 20 ± 2 °C and 65 ± 4 % relative humidity ensures that results are reproducible and comparable between laboratories and over time.
What is a jaw break and how is it handled?
A jaw break occurs when the specimen ruptures within 5 mm of the clamping line, often because of stress concentration at the grips rather than true fabric weakness. Such results are flagged, additional specimens are tested, and the treatment of jaw breaks is documented in the final report in accordance with the governing standard.
Are GB/T 3923 results comparable with ISO 13934 results?
GB/T 3923.1 and GB/T 3923.2 are Chinese national standards technically aligned with ISO 13934-1 and ISO 13934-2. For most commercial fabrics the results are directly comparable, although laboratories should verify the edition and any national deviations when results are used for formal certification.
How many specimens should be tested?
Fabric standards require a minimum of five valid specimens in each principal direction, yarn testing commonly requires ten individual strands, and additional specimens are tested whenever jaw breaks or abnormal ruptures occur, so that the reported mean is statistically representative of the sample.