Breaking Strength Test Methods: Standards, Procedures, and Applications

Breaking strength testing measures the maximum tensile force a material can withstand before rupture, making it one of the most fundamental indicators of quality and durability for fabrics, webbing, seams, and technical textiles. This guide explains internationally recognized breaking strength test methods, including the strip method, the grab method, and seam tensile testing, based on ISO, ASTM, EN, and GB standards. Read on to learn about sample preparation, equipment requirements, test procedures, calculation of results, and typical applications across apparel, industrial, and safety-critical product sectors.

Technical Overview

Breaking strength, also known as tensile strength or maximum force, is defined as the greatest force recorded when a test specimen is stretched longitudinally to rupture under specified conditions. It is expressed in newtons (N), although pounds-force (lbf) and kilogram-force (kgf) still appear in older specifications. Together with elongation at maximum force, breaking strength is the single most widely quoted mechanical property in textile specifications, purchase contracts, and quality-control release testing performed by accredited third-party laboratories.

The result of a breaking strength test depends strongly on how the test is performed. The width of the specimen, the gauge length, the rate of extension, the jaw type, and the conditioning atmosphere all influence the measured force. For this reason, international standards organizations have established tightly controlled procedures, and results are only comparable when the same method has been used. The principal standards include:

• ISO 13934-1, determination of maximum force and elongation at maximum force using the strip method
• ISO 13934-2, determination of maximum force using the grab method
• ASTM D5034, breaking strength and elongation of textile fabrics by the grab method
• ASTM D5035, breaking strength and elongation of textile fabrics by the strip method
• GB/T 3923.1 and GB/T 3923.2, Chinese national standards corresponding to the strip and grab methods
• ISO 13935-1 and ISO 13935-2, seam tensile properties using the strip and grab methods
• ASTM D1683, breaking strength and elongation of sewn seams in woven fabrics
• ISO 9073-3, tensile strength of nonwoven fabrics
• ISO 10319, wide-width tensile testing of geotextiles and related products
• ASTM D6775, breaking strength and elongation of textile webbing, tape, and woven cloth
• JIS L 1096, Japanese standard covering tensile testing methods for woven and knitted fabrics

All of these methods are designed for constant-rate-of-extension (CRE) tensile testing machines, in which one clamp remains stationary while the moving clamp extends the specimen at a constant speed. Older constant-rate-of-traverse (CRT) and constant-rate-of-loading (CRL) instruments are considered legacy equipment and are not accepted by current editions of most standards.

Testing Samples

Woven Fabrics

Woven fabrics are the primary scope of ISO 13934 and ASTM D5034/D5035. Specimens are cut in both the warp (lengthwise) and weft (widthwise) directions, because the two directions usually differ significantly in strength. Common product categories include denim, canvas, workwear fabrics, uniform cloth, bedding, lining fabrics, and filter cloth.

Knitted and High-Stretch Fabrics

Knitted fabrics can be tested for breaking strength, but their high elongation and tendency to neck down or roll at the edges require careful specimen preparation and appropriate pre-tension. Very stretchy materials may require modified gauge lengths or extension rates when the material specification permits, and results should always state the exact conditions used.

Nonwoven Fabrics

Nonwovens such as spunbond polypropylene, meltblown layers, needled felts, and interlinings are tested using ISO 9073-3 or equivalent strip-type procedures. Because nonwovens lack yarn structure, the cut edges are more prone to fiber pull-out, so specimen width control and edge quality are critical.

Webbing, Tapes, and Narrow Fabrics

Safety belts, lashing straps, harness webbing, elastic tapes, and other narrow fabrics are tested at full width rather than as cut strips, since cutting would destroy the structural selvedge that carries the load. ASTM D6775 is the typical reference method, and minimum breaking forces for such products are often safety-critical specification values.

Seams and Stitched Joints

Seam specimens consist of fabric pieces joined by a production seam, tested with the seam centered between the clamps. ISO 13935-1 (strip) and ISO 13935-2 (grab), along with ASTM D1683, measure the force required to break either the seam thread, the seam junction, or the fabric itself, thereby evaluating sewing thread selection, stitch density, and seam construction quality.

Coated, Laminated, and Technical Fabrics

Coated fabrics for tarpaulins, tents, inflatable structures, and protective clothing, as well as geotextiles for civil engineering, are tested using the same family of methods. For geotextiles, ISO 10319 specifies a wide-width strip specimen, typically 200 mm wide, because narrow specimens do not adequately represent the load distribution in soil-reinforcement applications.

Testing Items

A breaking strength test program can include the following measured and calculated parameters, depending on the standard and the product specification:

• Maximum force (breaking force): the peak force recorded before rupture, in newtons
• Breaking force per unit width: force normalized to specimen width, expressed in N/50 mm or N/cm, for fabrics where width varies
• Elongation at maximum force: the extension of the specimen at the moment the peak force is reached, expressed as a percentage of the initial gauge length
• Elongation at break: the extension at the moment of rupture, relevant for fabrics that continue to extend after the peak force
• Breaking tenacity: breaking force divided by the linear density of the yarns, used mainly for yarn and webbing comparisons
• Seam breaking strength: the maximum force sustained by a sewn seam, together with a record of the failure mode, such as thread breakage, fabric failure at the seam, or seam slippage
• Directional results: separate values for machine direction and cross-machine direction, or warp and weft
• Wet breaking strength: measured after water immersion where the material specification requires it, to evaluate strength retention in the wet state

Testing is normally performed in both principal directions, with a statistically defined number of specimens, and the reported result is a summary statistic, such as the median or the arithmetic mean, together with a measure of variability such as the coefficient of variation.

Testing Methods

Specimen Preparation and Conditioning

Samples are taken representative of the bulk material, at least 150 mm away from fabric edges, selvedges, or any treated zone. For the strip method, specimens are cut wider than the final test width and then raveled down to an effective width of 50 mm, so that all yarns are whole and run the full length of the specimen. For the grab method, specimens are cut directly to size with no raveling. At least five specimens are prepared in each direction, and no two specimens in the same direction should contain the same set of lengthwise yarns. All specimens are conditioned to moisture equilibrium in a standard atmosphere before testing: 20 °C ± 2 °C and 65 % ± 4 % relative humidity under ISO 139, or 21 °C ± 1 °C and 65 % ± 2 % relative humidity under ASTM D1776, typically for a minimum of 24 hours.

Strip Method (ISO 13934-1, ASTM D5035, GB/T 3923.1)

In the strip method, a specimen of full effective width is gripped across its entire width in both clamps, so that every yarn is loaded simultaneously. ISO 13934-1 specifies an effective specimen width of 50 mm, a gauge length of 200 mm, and a rate of extension of 20 mm/min, with a small pre-tension, typically 2 N for lighter fabrics and 5 N for heavier fabrics above approximately 200 g/m², applied to remove slack without stretching the specimen. ASTM D5035 uses raveled strips of 25 mm or 50 mm width, a gauge length of 75 mm, and a jaw speed of 300 mm/min. The strip method gives the most fundamental measure of fabric tensile strength and is preferred for specification purposes, research, and comparisons between fabrics of similar construction.

Grab Method (ISO 13934-2, ASTM D5034, GB/T 3923.2)

In the grab method, only the central portion of a wider specimen is gripped by the front jaw faces, typically 25 mm wide, while the outer yarns on each side remain unclamped and contribute to the strength through the fabric structure. ASTM D5034 specifies a specimen of approximately 100 mm × 150 mm, a gauge length of 100 mm, and a jaw speed of 300 mm/min; ISO 13934-2 uses a comparable specimen with a gauge length of 100 mm and a lower rate of 50 mm/min. The grab method is faster to prepare because no raveling is required, and it better reflects the strength of dense, coated, heavily sized, or difficult-to-ravel fabrics where individual yarns cannot be separated cleanly. Grab results are always higher than strip results on the same fabric and must never be interchanged in specifications.

Seam Tensile Method (ISO 13935-1, ISO 13935-2, ASTM D1683)

Seam specimens are prepared with the seam running perpendicular to the direction of loading and positioned midway between the clamps. The specimen is extended until failure occurs, and both the maximum force and the failure mode are recorded. The failure mode distinguishes between sewing-thread breakage, fabric rupture at the seam line, yarn slippage at the seam junction, and fabric failure away from the seam. This method is essential for garments, upholstery, protective equipment, and any product whose real-world integrity depends on the sewn joint rather than the fabric alone.

Equipment and Calibration

Testing is performed on a CRE universal tensile testing machine fitted with pneumatic or mechanical clamps with parallel, non-slip jaw faces. The force-measuring system must be verified and calibrated in accordance with ISO 7500-1 or ASTM E4, and the chosen force range should keep the anticipated breaking force between approximately 10 % and 90 % of the machine capacity to guarantee accuracy. Jaw faces may be plain, rubber-coated, serrated, or lined with auxiliary packing depending on the specimen, and the configuration must prevent both slippage and premature jaw-edge breakage. The extension-measuring system, gauge-length setting, and crosshead speed are checked as part of routine equipment qualification in accredited third-party laboratories.

Test Execution and Handling of Invalid Results

The specimen is mounted squarely in the clamps with the pre-tension applied, the crosshead is started, and the force-extension curve is recorded continuously until rupture. If the specimen slips in the jaws, breaks within 5 mm of the jaw line with a force lower than the median of valid results, or fails to break within the capacity of the machine, the result is discarded and a replacement specimen is tested. All discarded results are documented. The total number of valid observations per direction should meet the minimum of five required by the standards, or more where a tighter confidence interval is needed.

Data Processing and Reporting

ISO 13934-1 reports the median of the maximum force and the coefficient of variation for each direction, while ASTM methods report the arithmetic mean along with the standard deviation or coefficient of variation. A complete test report identifies the standard used, the method variant (strip or grab), specimen dimensions, gauge length, rate of extension, number of specimens, conditioning atmosphere, force values for each direction, elongation values, any wet-testing conditions, and the number and cause of discarded results. Clear identification of the method is essential because strip and grab values on the same fabric differ systematically and are not interchangeable.

Applications

Breaking strength testing supports quality control, product development, certification, and failure analysis across a broad range of industries:

• Apparel and workwear: verifying that denim, canvas, uniform fabrics, and protective clothing meet specified minimum strengths before shipment
• Home and contract textiles: quality release of bedding, upholstery, drapery, and mattress ticking fabrics
• Industrial textiles: tarpaulins, filtration fabrics, conveyor-belt fabrics, agricultural textiles, and coating substrates
• Geotextiles and civil engineering: wide-width tensile verification for soil reinforcement, separation, and drainage layers
• Automotive, aerospace, and transport: safety-belt webbing, airbag fabrics, seat fabrics, cargo restraint straps, and parachute materials
• Medical and hygiene products: nonwoven gowns, drapes, wound-care substrates, and adhesive fabric backings
• Packaging: woven polypropylene sacks, FIBC bulk-bag fabrics, and heavy-duty composite packaging
• Research and development: comparing fiber types, fabric constructions, finishes, and laundering or aging effects on tensile performance
• Regulatory compliance and claims substantiation: demonstrating conformity with buyer specifications, national standards, and labeling claims through accredited third-party laboratories

Because many safety-critical products define their minimum performance in terms of breaking force, this test is frequently a contractual release requirement and a key input to product liability documentation.

FAQ

What is the difference between the strip method and the grab method?

In the strip method, the full width of the specimen is clamped so that every yarn carries load directly, giving a fundamental measure of fabric tensile strength. In the grab method, only the central width is clamped while side yarns contribute indirectly, which makes preparation faster and suits dense or coated fabrics, but produces systematically higher values. Strip and grab results must never be compared directly or mixed within one specification.

Which standard should be chosen for a given fabric?

The choice is driven by the buyer specification, the destination market, and the fabric type. ISO 13934-1 and GB/T 3923.1 are the common references for strip testing in international and Chinese trade, ASTM D5034 or D5035 for North American requirements, and EN-based specifications within Europe. For nonwovens, webbing, and geotextiles, the dedicated standards ISO 9073-3, ASTM D6775, and ISO 10319 respectively should be used.

How many specimens are tested?

The standards require a minimum of five valid specimens in each direction of interest, warp and weft for wovens or machine and cross-machine direction for nonwovens and geotextiles. Additional specimens are tested whenever results are discarded or when a purchaser requires greater statistical confidence.

What is a jaw break, and how is it handled?

A jaw break is a rupture occurring at or within about 5 mm of the clamping line, usually caused by stress concentration at the jaw edge rather than true fabric strength. When such a break yields a force lower than the median of the valid results, the observation is discarded, the jaw-face type or lining is adjusted, and a replacement specimen is tested. The frequency of jaw breaks is noted in the report because it may indicate a testing-condition problem.

How does breaking strength differ from tear strength and seam slippage?

Breaking strength measures resistance to a steadily applied tensile load across the whole specimen, as covered by ISO 13934 and ASTM D5034/D5035. Tear strength measures the force needed to propagate an existing cut, using methods such as trouser or Elmendorf procedures. Seam slippage measures the displacement of yarns at a seam under load rather than rupture. These are complementary properties, and complete specifications usually address all three.

Which factors most strongly influence the test result?

Specimen width and raveling accuracy, gauge length, rate of extension, conditioning atmosphere, pre-tension, jaw alignment, and fabric moisture content all measurably affect the result. Consistent control of these parameters, and full disclosure of them in the test report, is what makes breaking strength values reproducible between laboratories.

Can elastic and knitted fabrics be tested for breaking strength?

Yes, but with caution. High-elongation knits may exceed the travel of the machine or deform at the clamps, so modified gauge lengths, reduced speeds, or specialized jaw facings may be required where the specification allows. The exact conditions must always be reported so that results remain comparable over time.