Breaking Strength Test Methods: Principles, Standards, and Laboratory Procedures

Breaking strength testing is one of the most fundamental mechanical evaluations for textiles, webbing, ropes, and technical materials, measuring the maximum tensile force a specimen can withstand before rupture. This article explains the internationally recognized breaking strength test methods—including the strip method, grab method, and cord testing—based on standards such as ISO 13934, ASTM D5034/D5035, and GB/T 3923. Read on to learn about specimen preparation, equipment requirements, test procedures, calculation of results, and practical applications across industries.

Technical Overview

Breaking strength refers to the maximum tensile force, expressed in newtons (N) or kilonewtons (kN), that a material can sustain before it ruptures under a gradually applied longitudinal load. The corresponding breaking strength test method is a cornerstone of quality control for textiles and flexible materials, because it directly reflects the structural integrity, durability, and safety margin of a product in service.

In a typical test, a prepared specimen of defined width and gauge length is clamped between two jaws of a universal tensile testing machine operating at a constant rate of extension (CRE). The machine applies an increasing force until the specimen fails, recording the maximum force (breaking force) and, in most configurations, the elongation at that force. The principal international standards governing these procedures include ISO 13934-1 and ISO 13934-2, ASTM D5035 and ASTM D5034, GB/T 3923.1 and GB/T 3923.2, JIS L 1096, and ISO 2307 for ropes and cords.

Manufacturers, brands, and accredited third-party laboratories rely on breaking strength data to verify incoming material quality, support product development, monitor production consistency, and demonstrate compliance with contractual or regulatory requirements in sectors ranging from apparel to automotive safety components.

Testing Samples

Woven Fabrics

Woven fabrics for apparel, home textiles, and industrial use are the most common samples. Specimens are cut in both the warp and weft directions to evaluate directional strength, since woven structures typically exhibit significantly different breaking forces along each axis.

Knitted Fabrics

Knitted materials are tested with special care because their loop structure causes high elongation and potential specimen slippage or curling. Wider specimens, auxiliary templates, or modified gripping methods may be applied to obtain valid failure in the gauge section.

Webbing, Straps, and Narrow Fabrics

Seat belt webbing, lifting slings, lashing straps, backpack tapes, and furniture webbing are tested at their full finished width whenever possible, because cutting a narrow fabric into strips destroys its structural unity and underestimates performance.

Ropes, Cords, and Twines

Fiber ropes and cords are evaluated under ISO 2307, which specifies specimen length, preconditioning cycles at a fraction of the nominal breaking force, and special capstan or bollard-type gripping arrangements to prevent premature failure at the jaws.

Elastic and Elastomeric Materials

Elastic bands, elastane-containing tapes, and covered rubber cords require cyclic loading or specified pre-extension before the breaking force is measured, ensuring that elastic recovery behavior does not distort the recorded result.

Nonwovens and Technical Textiles

Nonwoven geotextiles, filtration media, and medical textiles are tested according to dedicated procedures such as ISO 9073-3, which account for their anisotropic, bonded-fiber structure.

Testing Items

A breaking strength test program typically reports the following parameters, depending on the applicable standard and customer specification:

• Maximum force (breaking force): the highest force recorded before rupture, in N or kN.
• Breaking strength: breaking force normalized per unit width (N/50 mm, N/5 cm, or lbf/in), enabling comparison between materials of different widths.
• Elongation at maximum force: the extension of the specimen at the breaking point, expressed as a percentage of the initial gauge length.
• Elongation at specified force: extension measured at a contractually defined preload or working load.
• Breaking tenacity: breaking force divided by linear density (cN/tex), used primarily for yarns and cords.
• Work of rupture: the area under the force-extension curve, representing the energy absorbed before failure.
• Seam breaking strength: the force required to rupture a seamed specimen or cause seam failure, per ISO 13935-1 and ISO 13935-2.
• Failure mode and jaw-break incidents: documentation of where and how each specimen ruptured, which is essential for validating results.

Testing Methods

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

In the strip method, a long, narrow specimen—commonly 50 mm or 25 mm in width—is cut or raveled so that all yarns run parallel to the loading axis. With a gauge length of 200 mm and a test speed of 20 mm/min (yielding 10% extension per minute), the entire cross-section of the strip is stressed uniformly. The ravel strip technique removes edge yarns until the exact nominal width is achieved, ensuring that every yarn contributes to the measured breaking force. The strip method provides the most accurate assessment of intrinsic fabric tensile performance and is preferred for laboratory characterization and research.

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

In the grab method, a wider specimen (approximately 100 mm) is clamped only in its central region by jaws typically measuring 25 mm by 50 mm, leaving the outer portions unclamped. This configuration concentrates the stress on the gripped zone and better simulates localized loading conditions encountered in service, such as a seam or attachment point under stress. The grab method is faster to prepare, more tolerant of specimen preparation variability, and widely used for routine commercial acceptance testing of woven fabrics.

Rope and Cord Method (ISO 2307)

For ropes, a specimen of specified total length is mounted using bollard and capstan grips that distribute clamping pressure along the lay of the rope. The specimen is first cycled several times between zero and a specified pre-tension (commonly 1% to 10% of nominal breaking force) to consolidate the structure, after which the force is increased at a defined rate until rupture. The reported breaking force is corrected for the measured linear density of the specimen.

Equipment and Instrumentation

All methods require a calibrated universal testing machine operating in constant-rate-of-extension mode, equipped with:

• Pneumatic or mechanical jaws with flat, grooved, or lined faces appropriate to the material, with a clamping force sufficient to prevent slippage without cutting the specimen.
• A calibrated force sensor (load cell) with a capacity matched to the expected breaking force, so that the result falls within the calibrated range.
• An extensometer or crosshead displacement measurement system for recording elongation.
• Data acquisition software capable of plotting the force-extension curve and identifying the maximum force and failure point.

Specimen Preparation and Conditioning

Specimens are cut from positions representing different areas of the sample, kept at least 150 mm away from the fabric selvedge, and oriented so that no two warp-direction specimens share the same set of yarns. Edges must be parallel, fraying is controlled by raveling or careful cutting, and specimens are conditioned to equilibrium in the standard textile atmosphere of 20 ± 2 °C and 65 ± 4% relative humidity as defined in ISO 139 before testing. A minimum of five valid specimens per direction is generally required, with the median or mean reported according to the governing standard.

Test Procedure

• Verify machine calibration, jaw alignment, and load cell suitability for the expected force range.
• Mount the specimen centrally in the jaws with the yarns parallel to the direction of force, without slack or pre-tension beyond the specified amount.
• Set the gauge length and extension rate specified by the standard (for example, 200 mm and 20 mm/min for ISO 13934-1).
• Start the test and continue until the specimen ruptures, monitoring for slippage or jaw breaks.
• Record the maximum force, elongation at maximum force, and failure location for each specimen.
• Repeat for all specimens in each required direction, then calculate the mean, and where required, the coefficient of variation.
• Discard and replace results affected by jaw breaks—failures occurring at the jaw line or within the jaws—when they exceed the allowance stated in the standard.

Calculation and Expression of Results

The breaking force is reported as the mean of valid specimens in N (or kN for high-strength materials such as webbing and ropes), rounded according to standard practice. Breaking strength is obtained by referencing the force to the specimen width, for example N/50 mm. Elongation at break is calculated as the extension at maximum force divided by the initial gauge length and multiplied by 100. For yarns and cords, breaking tenacity is expressed in cN/tex by dividing the breaking force by the measured linear density. Test reports must also identify the standard used, the method variant (strip or grab), conditioning details, machine parameters, and any deviations or invalid failures.

Applications

Breaking strength test methods are applied across a broad spectrum of industries and product categories:

• Apparel and home textiles: verifying that fabrics meet minimum strength specifications for durability claims and labeling.
• Automotive safety components: qualification and batch control of seat belt webbing, tether straps, and airbag fabrics.
• Personal protective equipment: strength verification of harness webbing, lanyards, and load-bearing textile components.
• Lifting and cargo securing: certification of lifting slings and lashing systems against declared working load limits.
• Geotextiles and construction: tensile evaluation of reinforcement and separation fabrics used in civil engineering works.
• Medical textiles: strength testing of bandages, surgical fabrics, and single-use protective materials.
• Packaging and industrial materials: quality control of strapping tapes, filter fabrics, and coated technical textiles.
• Military and outdoor equipment: qualification of tent fabrics, climbing cord, parachute materials, and load-carrying equipment.

FAQ

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

The strip method grips the full width of a narrow specimen, stressing every yarn uniformly and giving an accurate measure of intrinsic fabric strength. The grab method clamps only the central portion of a wider specimen, concentrating stress in a localized zone and better simulating point-loading in real use. Strip results are typically used for characterization, while grab results are common for commercial acceptance testing; the two methods are not interchangeable.

Why do ISO and ASTM results for the same fabric sometimes differ?

Differences in specimen width, gauge length, jaw design, extension rate, and calculation conventions between standards such as ISO 13934-2 and ASTM D5034 can produce systematically different breaking forces. For this reason, test reports must always state the exact standard applied, and comparisons should only be made between results obtained under the same conditions.

What is a jaw break and how is it handled?

A jaw break occurs when the specimen ruptures at or inside the clamping jaws rather than in the gauge section, usually because of stress concentration or jaw damage to the material. Such results are considered unrepresentative. Depending on the standard, they are noted, and if their proportion exceeds the permitted allowance, the batch is retested using modified clamping pressure, jaw lining, or an alternative gripping technique.

How many specimens are required for a valid test?

Most standards require a minimum of five valid specimens for each test direction (warp and weft, or machine and cross direction). Additional specimens may be tested to replace invalid results caused by jaw breaks, slippage, or preparation defects.

Can breaking strength tests be performed on seams?

Yes. Seam efficiency is evaluated using ISO 13935-1 (strip method) and ISO 13935-2 (grab method), in which a seam is placed centrally in the gauge length. The test determines whether failure occurs in the fabric, at the seam line, or by thread breakage, which is critical information for garment and technical product construction.

In what units is breaking strength reported?

Breaking force is reported in newtons (N) or kilonewtons (kN). When normalized for width, results are expressed as N/50 mm or equivalent; for yarns and cords, breaking tenacity is given in cN/tex. Some legacy specifications in certain markets still reference pounds-force (lbf), which accredited laboratories can report alongside SI units when required.