Breaking strength testing measures the maximum tensile force a material can withstand before rupture, making it one of the most widely performed mechanical evaluations in quality control and product certification. This guide explains the key breaking strength test standards published by ISO, ASTM, EN, and GB organizations, covering specimen preparation, test procedures, equipment requirements, and reporting rules. Whether you work with textiles, plastics, yarns, or industrial materials, understanding these standards ensures accurate, comparable, and internationally accepted test results.
Technical Overview
Breaking strength, also called breaking force or maximum force, is the highest tensile load a specimen sustains immediately before rupture when it is stretched to failure under controlled laboratory conditions. Because the measured value is highly sensitive to test variables, breaking strength test standards strictly define specimen dimensions, gauge length, extension rate, jaw geometry, clamping pressure, conditioning atmosphere, and data-processing rules. This standardization allows results from different laboratories and different countries to be directly compared.
The principal breaking strength test standards are developed and maintained by international and national standards bodies, including ISO (International Organization for Standardization), ASTM International (ASTM), CEN (European EN standards), the SAC (Chinese GB standards), and JSA (Japanese JIS standards). Although the technical content of these standards is largely harmonized, differences in gauge length, test speed, and specimen width mean that the specific standard used must always be stated in test reports.
Core Standards Reference List
- ISO 13934-1 / EN ISO 13934-1 / GB/T 3923.1 — Textiles: tensile properties of fabrics, strip method for determination of maximum force and elongation at maximum force
- ISO 13934-2 / EN ISO 13934-2 / GB/T 3923.2 — Textiles: tensile properties of fabrics, grab method
- ASTM D5034 — Breaking strength and elongation of textile fabrics (grab test)
- ASTM D5035 — Breaking force and elongation of textile fabrics (strip test)
- ASTM D2256 / ISO 2062 / GB/T 3916 — Tensile properties of yarns by the single-thread method
- ISO 527-1 and ISO 527-3 / ASTM D638 / GB/T 1040 — Tensile properties of plastics and plastic films
- ASTM D882 — Tensile properties of thin plastic sheeting and films
- ASTM D76 — Specification for tensile testing machines for textiles
- ISO 139 / ASTM D1776 — Standard atmospheres for conditioning and testing textiles
- ISO 10319 — Wide-width tensile testing of geotextiles and related products
Testing Samples
Breaking strength test standards apply to a broad range of materials, and each material category has dedicated specimen requirements. Typical sample types submitted to accredited third-party laboratories include the following.
Woven and Knitted Fabrics
Apparel fabrics, home textiles, technical fabrics, and coated fabrics are tested in both the warp (lengthwise) and weft (widthwise) directions. Specimens are cut with their long axis parallel to the direction being tested, and selvage edges are avoided. Raveled-strip preparation removes edge yarns so the specimen is an exact, whole number of threads wide.
Yarns and Sewing Threads
Spun and filament yarns, industrial threads, and elastic yarns are tested as single ends wound onto specially designed yarn grips or caps. Conditioning on standardized bobbins prevents tension differences from affecting results.
Nonwovens and Geotextiles
Nonwoven fabrics are tested using grab or strip procedures, while geotextiles require wide-width specimens per ISO 10319 because narrow strips fail by progressive yarn pull-out rather than tensile rupture.
Plastic Films and Sheets
Flexible packaging films, laminates, and sheets thinner than 1 mm are tested per ASTM D882 or ISO 527-3 using rectangular strips, while thicker plastics use machined dog-bone (dumbbell) specimens per ASTM D638, ISO 527-2, or GB/T 1040.
Webbing, Straps, and Narrow Fabrics
Seatbelt webbing, lifting slings, lashing straps, hook-and-loop fasteners, and ribbon tapes are tested at full product width because the entire construction contributes to the breaking strength.
Elastomeric and Coated Materials
Rubber sheets, elastic bands, coated fabrics, and composite laminates are tested with elongation-appropriate gauge lengths and speeds, often with specialized jaw liners to prevent slippage without initiating premature failure.
Testing Items
A standard breaking strength test report issued under these standards typically includes the following measured and calculated parameters.
- Breaking force (maximum force): the peak load recorded before rupture, expressed in newtons (N) or pounds-force (lbf)
- Elongation at maximum force: extension of the specimen at the moment the peak load is reached, expressed as a percentage of the initial gauge length
- Elongation at break: extension at the instant of rupture, expressed as a percentage
- Tenacity: breaking force normalized by linear density, expressed in cN/tex, N/tex, or gf/denier, used mainly for yarns and fibers
- Breaking tenacity and knot tenacity for yarns tested per ASTM D2256
- Work to rupture (toughness): the total energy absorbed up to break, expressed in joules (J)
- Initial modulus: the slope of the initial linear region of the force-extension curve
- Statistical results: arithmetic mean, range, standard deviation, and coefficient of variation (CV%) for the valid specimen population
Testing Methods
Strip Method (ISO 13934-1, ASTM D5035, GB/T 3923.1)
In the strip method, the full width of the specimen is gripped in both jaws. ISO 13934-1 specifies a 50 mm specimen width and a 200 mm gauge length for most woven fabrics, with a separation rate of 20 mm/min when elongation at break does not exceed 75%, and 100 mm/min for highly extensible materials. ASTM D5035 offers both 25 mm and 50 mm strip options with 75 mm or 200 mm gauge lengths. The strip method evaluates the strength contributed by every yarn across the specimen width and is considered the more fundamental measure of fabric tensile strength.
Grab Method (ISO 13934-2, ASTM D5034, GB/T 3923.2)
In the grab method, only the central portion of a wider specimen is clamped, typically using 25 mm front jaw faces on a specimen approximately 100 mm wide. ISO 13934-2 specifies a 100 mm gauge length and a 50 mm/min separation rate, while ASTM D5034 uses a 75 mm grip separation at 300 mm/min. The grab method better represents fabric performance in service conditions where localized stress concentrations occur, such as seam areas and pinning points, and is less affected by edge yarn damage.
Single-End Yarn Method (ASTM D2256, ISO 2062, GB/T 3916)
Yarns are tested individually using a 500 mm gauge length with a constant rate of extension, commonly 500 mm/min for most spun and filament yarns per ISO 2062. A standardized pretension, typically 0.5 cN/tex, is applied before extension begins to remove slack without stressing the yarn. Tenacity is calculated by dividing the breaking force by the yarn linear density.
Plastics Tensile Method (ISO 527, ASTM D638, ASTM D882, GB/T 1040)
Rigid and semi-rigid plastics are tested using machined dog-bone specimens (Type 1A/1B under ISO 527, Type I under ASTM D638) with a 50 mm gauge length and speeds from 1 to 500 mm/min selected according to the material specification. Thin films below 1 mm thickness are tested as rectangular strips per ASTM D882 or ISO 527-3, with the separation rate chosen to produce rupture within the time window defined by the standard.
Conditioning and Equipment Requirements
Textile specimens must be conditioned in the standard atmosphere defined by ISO 139 or ASTM D1776 (20 ± 2 °C and 65 ± 4 % relative humidity, or 21 °C and 65 % RH in ASTM practice) before testing, while plastics are conditioned per ISO 291 (typically 23 ± 2 °C and 50 ± 5 % RH). Testing machines must operate on the constant-rate-of-extension (CRE) principle, as required by ISO 13934 and ASTM D5034/D5035, and must meet the calibration and verification requirements of ASTM D76 and ISO 7500-1. Older constant-rate-of-loading (CRL) and constant-rate-of-traverse (CRT) instruments are no longer accepted by the current editions of these standards.
Data Processing and Validity Criteria
At least five valid breaks in each test direction are normally required. Results from specimens that slip in the jaws, break within 5 mm of the jaw line, or fail outside the gauge region in strip tests are treated as invalid and are replaced by additional specimens, provided the discard criteria and statistical checks defined in the standard are satisfied. The final result is reported as the arithmetic mean of valid breaks together with the coefficient of variation, the specific standard and method used, machine type, gauge length, speed, and conditioning details.
Applications
Breaking strength test standards support quality control, product development, and regulatory compliance across virtually every industry that manufactures or processes flexible and rigid materials.
- Apparel and footwear: verifying fabric strength, seam integrity, and thread tenacity before bulk production release
- Home and contract textiles: qualifying bedding, upholstery, and curtain fabrics against retail specification limits
- Geotextiles and civil engineering: wide-width tensile verification for reinforcement and separation fabrics in road, rail, and landfill construction
- Medical textiles: strength confirmation for bandages, surgical gowns, and wound-care substrates
- Automotive and transportation: tensile qualification of interior fabrics, airbag textiles, seatbelt webbing, and cargo restraint straps
- Flexible packaging: film tensile strength and elongation checks for laminates, pouches, and seal materials
- Ropes, cords, and industrial yarns: lot-acceptance testing and guaranteed minimum strength verification
- Supplier and trade compliance: independent verification of test data by ISO/IEC 17025-accredited third-party laboratories for buyers, customs, and certification bodies
FAQ
What is the difference between the strip method and the grab method?
The strip method grips the full width of the specimen and measures the true tensile strength of the fabric structure, whereas the grab method grips only the central portion of a wider specimen and better reflects performance under localized stress, similar to conditions near seams or attachment points. ISO 13934-1 and ASTM D5035 cover the strip method, while ISO 13934-2 and ASTM D5034 cover the grab method. Grab results are generally higher than strip results for the same fabric and the two methods are not interchangeable.
Why do current standards require a CRE-type testing machine?
A constant-rate-of-extension machine separates the jaws at a precisely controlled, uniform speed, which produces reproducible force-extension curves independent of specimen stiffness. Constant-rate-of-traverse (CRT) screw-driven machines, historically common in textile mills, introduce speed errors on stiff specimens, so ISO 13934, ISO 2062, and ASTM D5034/D5035 now specify CRE instrumentation exclusively.
What happens if a specimen breaks inside the jaws?
A break occurring at or near the jaw line is usually caused by stress concentration or jaw damage rather than true tensile failure. Such results are flagged, statistically evaluated, and typically discarded, with replacement specimens tested. If jaw breaks persist, the laboratory should adjust jaw pressure, use different jaw liner materials, or modify the gripping technique as permitted by the standard.
How many specimens must be tested?
Most fabric standards require a minimum of five valid breaks in the lengthwise direction and five in the widthwise direction, for ten specimens in total. Yarn standards such as ISO 2062 require at least ten valid individual breaks, and additional specimens are tested whenever invalid results are rejected.
How are breaking strength units converted?
SI reporting uses newtons (N) or kilonewtons (kN). For reference, 1 kgf equals 9.807 N and 1 lbf equals 4.448 N. Yarn results are commonly normalized to tenacity in cN/tex, where 1 N/tex equals 100 cN/tex.
Is conditioning really necessary before testing?
Yes. Most fibers, films, and elastomers absorb atmospheric moisture, which measurably changes their strength and elongation. Conditioning to the standard atmosphere defined in ISO 139, ASTM D1776, or ISO 291 ensures that the moisture content of the specimen is in equilibrium before loading, which is a prerequisite for valid and comparable results.