Breaking Strength Testing Procedure: A Complete Technical Guide for Textile Inspection

Breaking strength testing is one of the most fundamental procedures in textile and material quality control, measuring the maximum tensile force a specimen can withstand before rupture. This technical guide explains the complete breaking strength inspection procedure, covering applicable standards such as ISO 13934, ASTM D5034, ASTM D5035, and GB/T 3923, along with equipment requirements, specimen preparation, test conditions, and result evaluation. Whether you perform testing in an in-house laboratory or through accredited third-party laboratories, this article provides the essential technical framework for reliable and repeatable tensile testing.

Technical Overview

Breaking strength, also known as breaking force or tensile breaking strength, is defined as the maximum force recorded by a tensile testing machine while a specimen is being extended longitudinally to rupture. It is expressed in newtons (N) and serves as a primary indicator of the mechanical integrity of textile fabrics, yarns, and related materials. A formalized breaking strength inspection procedure is essential because tensile results are highly sensitive to test conditions, specimen geometry, clamping method, and environmental atmosphere.

The procedure documented here establishes uniform requirements for apparatus, atmospheric conditioning, sampling, specimen preparation, operating steps, calculation of results, and test reporting. It aligns with the internationally recognized methodology of constant rate of extension (CRE) tensile testing and supports acceptance testing, quality control, research, and certification activities performed by manufacturers and accredited third-party laboratories.

• ISO 13934-1 — Textiles — Tensile properties of fabrics — Part 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 — Standard Test Method for Breaking Strength and Elongation of Textile Fabrics (Grab Test)
• ASTM D5035 — Standard Test Method for Breaking Force and Elongation of Textile Fabrics (Strip Test)
• 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 — Determination of seam maximum force using the strip and grab methods
• ISO 2062 — Determination of single-end breaking force and elongation of yarns
• ISO 139 — Standard atmospheres for conditioning and testing textiles

Testing Samples

Woven Fabrics

Woven fabrics are the primary scope of the breaking strength procedure. Specimens are cut in both the warp (lengthwise) and weft (crosswise) directions so that the directional strength characteristics of the fabric can be evaluated independently. For raveled strip testing, specimens are cut wider than the final test width and the edge yarns are removed to achieve a precise effective width.

Knitted Fabrics

Knitted fabrics generally exhibit high elongation and low lateral stability, which can cause curling, transverse contraction, and specimen damage during clamping. When strip testing is applied, modified specimen preparation, increased care in mounting, or alternative methods such as bursting strength testing in accordance with ISO 13938 should be considered.

Nonwoven and Coated Fabrics

Nonwoven fabrics are tested in accordance with ISO 9073-3, while rubber- or plastic-coated fabrics follow ISO 1421. These materials typically use cut strips without raveling, and specimen dimensions and extension rates follow the specific requirements of the applicable standard.

Yarns and Threads

Single-end yarns and sewing threads are evaluated using ISO 2062 or equivalent national standards. Testing is performed on creel-mounted packages with a defined gauge length and pre-tension to determine breaking force, breaking tenacity in centinewtons per tex (cN/tex), and elongation at break.

Narrow Fabrics, Webbing, and Elastics

Webbing, tapes, ribbons, braids, and elastic narrow fabrics are tested at their full manufactured width without width reduction. The relevant specifications are usually defined in product standards, purchase contracts, or military and technical specifications.

Testing Items

The inspection procedure covers the following measured and calculated parameters, each of which must be reported with its direction of application relative to the fabric.

• Maximum force (breaking force), expressed in newtons (N) or kilonewtons (kN)
• Elongation at maximum force, expressed as a percentage of the initial gauge length
• Breaking tenacity, expressed in cN/tex or N/tex for yarns and strip-type materials of known linear density
• Work to break (toughness), expressed in joules (J), derived from the force-extension curve
• Seam maximum force for seamed specimens, in accordance with ISO 13935
• Statistical evaluation of results, including arithmetic mean, coefficient of variation, and 95 percent confidence interval

Testing Methods

Testing Principle and Apparatus

A specimen of specified dimensions is clamped between two jaws of a CRE (constant rate of extension) tensile testing machine. The upper jaw remains stationary while the lower extending clamp moves at a constant rate until the specimen ruptures. The electronic force-measuring system records the force-extension curve, from which the maximum force and elongation at maximum force are obtained. CRT (constant rate of traverse) and CRL (constant rate of loading) instruments may still be encountered, but CRE machines are the reference type in current editions of ISO and ASTM standards.

The apparatus shall meet the following requirements:

• Force measuring and indicating system verified in accordance with ISO 7500-1 or ASTM E4, with the selected force range placing the expected breaking force between 10 and 90 percent of full capacity
• Adjustable gauge length, typically 200 mm for the strip method and 100 mm for the grab method, with a length indicator accurate to the nearest 1 mm
• Jaw faces of suitable size, surface texture, and material to grip the specimen without slippage or jaw-edge damage; pneumatic, hydraulic, or manual clamping with interchangeable faces is permitted
• Constant rate of extension accurate to the tolerance specified in the standard, commonly 20 mm/min, 100 mm/min, or other specified values

Conditioning and Test Atmosphere

Specimens shall be conditioned in the relaxed state in one of the standard atmospheres defined in ISO 139 before testing. The preferred standard atmosphere is (20 ± 2) °C and (65 ± 4) percent relative humidity; the tropical alternative is (27 ± 2) °C and (65 ± 4) percent relative humidity. Conditioning is continued until moisture equilibrium is reached, which generally requires a minimum of 24 hours for most fabrics. All testing shall be carried out in the same atmosphere in which the specimens were conditioned, and the atmosphere shall be recorded in the test report.

Specimen Preparation

Cut specimens representative of the full width of the fabric, avoiding selvage regions, fold creases, visibly damaged areas, and sections with the same lengthwise yarns appearing in more than one specimen. Unless otherwise specified, prepare at least five specimens for each test direction, with additional specimens retained for retesting in case of slippage or jaw breaks.

• Strip method: specimens approximately 300 mm long and 60 mm wide, raveled to an effective width of 50 mm for woven fabrics; cut strips of 50 mm width are used where raveling is impractical
• Grab method: specimens of sufficient width to span the jaws with the central portion clamped, commonly 100 mm by 100 mm, with the clamped width equivalent to the jaw face width
• Yarn method: single-end specimens at the gauge length specified in ISO 2062, typically 500 mm, mounted with standardized pre-tension
• All specimens are marked and identified by direction (warp, weft, machine direction, cross direction, or thread path)

Test Procedure

• Verify the calibration status of the tensile tester and select the force range appropriate to the expected breaking force.
• Set the gauge length and the rate of extension as specified by the governing standard; for example, 200 mm gauge length at 20 mm/min in the ISO strip method, or the rate specified in ASTM D5034 for grab testing.
• Clamp the first specimen in the jaws, ensuring it is centered, parallel to the direction of force application, and free of wrinkles or twist; apply the specified pre-tension where required.
• Start the test and record the force-extension curve up to rupture; note the maximum force and elongation at maximum force.
• Examine the broken specimen; if the break occurred within the jaws, or if slippage is evident, discard the result and repeat the test with a replacement specimen.
• Repeat the sequence for the remaining specimens in each test direction until the required number of valid results is obtained.

Calculation and Expression of Results

For each direction, calculate the arithmetic mean of the valid individual breaking force values, expressed in newtons to three significant figures, and the mean elongation at maximum force as a percentage. Where required, calculate the coefficient of variation and the 95 percent confidence interval to characterize dispersion. Breaking tenacity is calculated by dividing the breaking force by the linear density of the test specimen. Individual values deviating markedly from the group shall be investigated; results from specimens that broke in the jaws or slipped are excluded from statistical treatment.

Test Report

The test report shall be complete, traceable, and unambiguous, and shall include at least the following elements:

• Identification and description of the sample, including fabric construction and direction of test
• The test standard and method used (strip or grab) and any deviations from the procedure
• Type of tensile tester, force range, gauge length, rate of extension, and jaw type
• The conditioning and testing atmosphere
• Number of specimens tested and number of results discarded with reasons
• Mean breaking force, mean elongation at maximum force, and any statistical parameters required
• Date of test and identification of the operator or laboratory

Applications

The breaking strength inspection procedure is applied across the entire textile value chain, from raw material qualification to finished product release. Typical fields of application include:

• Incoming inspection of greige and finished woven fabrics for garment and home textile production
• Verification of mechanical performance for industrial textiles, filter fabrics, conveyor belt fabrics, and tarpaulins
• Geotextile qualification, often supplemented by wide-width tensile testing in accordance with ISO 10319
• Medical textile evaluation, including gauze, bandage, and surgical drape strength verification
• Automotive interior textile assessment against OEM technical specifications
• Seam strength verification of stitched assemblies in workwear, protective clothing, and upholstery
• Research and development support for fiber selection, fabric construction optimization, and finish durability studies
• Regulatory compliance and certification testing conducted by accredited third-party laboratories

FAQ

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

The strip method tests the entire width of a narrow specimen, so all yarns within the effective width carry the load, and it better reflects the intrinsic strength of the yarns and fabric structure. The grab method clamps only the central portion of a wider specimen, allowing yarns at the unclamped edges to contribute partially; it is faster, more tolerant of specimen preparation, and widely used for acceptance testing of robust woven fabrics.

Which type of tensile testing machine is required?

Current ISO and ASTM standards designate CRE (constant rate of extension) machines as the reference apparatus. Results from CRT or CRL instruments are not directly comparable and should only be used when contractually agreed and clearly identified in the report.

How many specimens should be tested?

A minimum of five valid specimens per test direction is the general requirement for fabric testing. Additional specimens should be prepared so that tests invalidated by jaw breaks or slippage can be replaced without re-sampling.

Why is atmospheric conditioning necessary before testing?

The moisture content of hygroscopic fibers such as cotton, viscose, and wool directly affects tensile performance. Conditioning in the standard atmosphere of 20 ± 2 °C and 65 ± 4 percent relative humidity ensures reproducible and comparable results between laboratories and over time.

What should be done if the specimen breaks in the jaws or slips during testing?

Such results are considered invalid and shall be discarded. Corrective actions include changing jaw face material or texture, adjusting clamping pressure, adding protective tabs or liners at the grip points, or modifying the gauge length if permitted by the governing standard. All discarded results and the reasons for rejection shall be documented in the test report.