Breaking Strength Testing to Chinese National Standards (GB): Methods, Samples, and Compliance Guide

Breaking strength testing in accordance with Chinese national standards (GB standards) determines the maximum tensile force a material can withstand before rupture, providing essential data for quality control, conformity assessment, and market access in China. This guide explains the principal GB test methods for breaking strength across textiles, nonwovens, plastics, rubber, and metals, including specimen requirements, test items, equipment, and typical applications. Because many GB methods are harmonized with ISO and comparable to ASTM procedures, understanding them helps manufacturers and quality engineers obtain accurate, mutually recognized test results.

Technical Overview

Breaking strength, also referred to as breaking force or tensile strength, is the maximum force recorded when a test specimen is stretched to rupture under controlled tensile loading. In China, this testing discipline is governed by the national standards system, in which standards carrying the prefix GB are mandatory technical regulations while standards carrying the prefix GB/T are recommended national standards. Although the underlying test methods are published as GB/T documents, breaking strength requirements become binding when they are cited by mandatory GB codes, product standards, procurement contracts, or market supervision rules.

The most widely applied field for breaking strength testing is textiles, where the core national standards are GB/T 3923.1 (strip method) and GB/T 3923.2 (grab method). These methods are technically aligned with ISO 13934-1 and ISO 13934-2 and are broadly comparable to ASTM D5035 and ASTM D5034, allowing laboratories to report results that are accepted across international supply chains.

• GB/T 3923.1 - Determination of maximum force and elongation at maximum force of fabrics using the strip method
• GB/T 3923.2 - Determination of maximum force of fabrics using the grab method
• GB/T 3916 - Determination of breaking force and elongation at break of single-end yarns
• GB/T 13772 series - Determination of yarn slippage resistance at seams
• GB/T 13773 series - Determination of seam tensile properties by strip and grab methods
• GB/T 3917 series - Determination of tearing force by pendulum, trouser, wing, and tongue methods
• GB/T 7742.1 - Determination of bursting strength by the hydraulic method
• GB/T 19976 - Determination of bursting strength by the steel ball method
• GB/T 24218.3 - Determination of tensile strength and elongation of nonwoven fabrics
• GB/T 15788 - Wide-width tensile testing of geotextiles and related products
• GB/T 1040 series - Determination of tensile properties of plastics, aligned with ISO 527
• GB/T 528 - Determination of tensile stress-strain properties of vulcanized rubber, aligned with ISO 37
• GB/T 228.1 - Tensile testing of metallic materials at room temperature, aligned with ISO 6892-1
• GB/T 12914 - Determination of tensile properties of paper and board

Test Principle and Equipment

All GB breaking strength methods are based on the same principle: a conditioned specimen is gripped between two jaws of a constant-rate-of-extension (CRE) tensile testing machine and extended along its axis until rupture. The force-elongation curve is recorded, and the maximum force, elongation at maximum force, and work of rupture are extracted. The testing machine must be calibrated and verified for force accuracy, typically in accordance with ISO 7500-1, using a load range appropriate to the expected strength of the specimen. Textile specimens are conditioned in the standard atmosphere specified in GB/T 6529, namely 20 ± 2 degrees Celsius and 65 ± 4 percent relative humidity, normally for a minimum of 24 hours or until moisture equilibrium is reached.

Testing Samples

Woven Fabrics

Woven fabrics are the primary sample type for GB/T 3923.1 and GB/T 3923.2. Specimens are cut in both the lengthwise (warp) and widthwise (weft) directions, taken at least one meter from the end of the fabric roll and distributed across the width while avoiding the selvedge region and any creases, folds, or visible defects.

Knitted Fabrics

Because knitted structures are highly extensible and prone to jaw damage in direct tensile testing, they are usually evaluated for bursting strength using GB/T 7742.1 (hydraulic method) or GB/T 19976 (steel ball method) rather than strip or grab tensile methods.

Nonwoven Fabrics

Nonwoven materials for hygiene, filtration, and medical applications are tested in machine and cross-machine directions using the tensile method in GB/T 24218.3, which follows the general strip-test principle adapted for bonded fiber webs.

Yarns and Sewing Threads

Single-end yarns, sewing threads, and elastomeric filaments are evaluated with GB/T 3916, which measures breaking force, breaking tenacity, and elongation at break of individual strands wound on packages.

Plastics, Rubber, and Metal Materials

Rigid and flexible plastics are tested with the GB/T 1040 series using dumbbell or strip specimens; vulcanized and thermoplastic rubbers are tested with GB/T 528 using dumbbell specimens; metallic materials are tested with GB/T 228.1 using machined proportional or non-proportional test pieces. Geotextiles and coated fabrics are tested with GB/T 15788 using wide-width specimens to reduce clamping effects.

Testing Items

The scope of breaking strength evaluation under the GB system typically includes the following reported parameters:

• Breaking force or maximum force, expressed in newtons (N)
• Elongation at maximum force and elongation at break, expressed as a percentage
• Breaking tenacity for yarns, expressed in cN/tex
• Seam breaking strength, assessed with the GB/T 13773 series
• Seam slippage resistance, assessed with the GB/T 13772 series
• Tearing force, assessed with the GB/T 3917 series, including pendulum tear strength in millinewtons
• Bursting strength, expressed in kilopascals for the hydraulic method or newtons for the steel ball method
• Coefficient of variation of the individual results and the number of valid specimens tested

Test reports prepared by accredited third-party laboratories must identify the standard applied, specimen direction, conditioning atmosphere, machine type and rate, and any deviations such as discarded jaw breaks, so that results can be independently reviewed and reproduced.

Testing Methods

Strip Method (GB/T 3923.1)

At least five specimens are prepared in each principal direction. The effective specimen width is 50 mm, achieved either by cutting accurately or by raveling a 60 mm cut strip down to 50 mm. A gauge length of 200 mm with an extension rate of 20 mm/min is used when elongation does not exceed 75 percent; for highly extensible fabrics, a 100 mm gauge at 100 mm/min applies. Pretension is set according to fabric mass, commonly 2 N for fabrics up to 200 g/m2, 5 N for 200 to 500 g/m2, and 10 N above 500 g/m2. Specimens that slip in the jaws or break within 5 mm of the jaw edge and yield abnormally low values are discarded and replacement specimens are tested.

Grab Method (GB/T 3923.2)

The grab method evaluates the effective strength of a wider fabric area and is preferred for high-strength, coated, or difficult-to-ravel fabrics. Specimens of approximately 100 mm by 150 mm are gripped centrally by jaws that hold only the middle portion, with a gauge length of 100 mm and an extension rate of 50 mm/min. Five specimens per direction are tested and the mean maximum force is reported.

Single-Yarn Method (GB/T 3916)

Individual yarns are extended using a 500 mm gauge length, typically at 500 mm/min or at a rate adjusted so that rupture occurs within approximately 20 seconds. A small pretension is applied to remove slack before extension begins. Breaking force, breaking tenacity, elongation at break, and their coefficients of variation are reported for a minimum of ten valid breaks per package.

Seam and Slippage Tests (GB/T 13772 and GB/T 13773)

Seam performance is evaluated on specimens containing a standardized seam, using strip or grab geometry to measure seam breaking strength, or by measuring the load required to produce a defined seam opening when the fabric is stressed. These methods simulate the stresses seams experience during garment wear and household laundering of bedding and furnishing textiles.

Bursting Strength (GB/T 7742.1 and GB/T 19976)

In the hydraulic method, a clamped circular specimen is pressurized by fluid behind an elastic diaphragm over a standard test area until rupture, with the volume-increase rate selected so that bursting occurs within the time window specified in the standard. In the steel ball method, a polished steel ball of 25 mm diameter is driven through a specimen held by a ring clamp at a controlled speed, and the maximum force is recorded. Both methods are suitable for knitted fabrics, nonwovens, and lace where multidirectional strength matters.

Calculation and Expression of Results

For all methods, the arithmetic mean of all valid individual results is calculated and reported together with the coefficient of variation. Results are reported in newtons for tensile and ball-burst tests, kilopascals for hydraulic bursting, and percent for elongation values, with the specimen directions clearly identified as lengthwise and widthwise or machine and cross-machine.

Applications

Breaking strength data generated under GB national standards support a wide range of commercial and regulatory purposes:

• Product compliance for apparel, bedding, towels, and home textiles, where product standards specify minimum breaking force, seam strength, or bursting strength limits
• Quality control during fabric production, dyeing, and finishing, including detection of strength loss caused by chemical processing
• Technical textiles such as geotextiles, filtration media, coating substrates, and construction fabrics, where mechanical reliability is a safety requirement
• Medical and hygiene textiles, including nonwoven surgical gowns, drapes, and masks, verified against recognized test methods
• Personal protective equipment and workwear, where fabric and seam strength contribute to certification under mandatory safety codes
• Import and export trade, where ISO-harmonized GB test reports from accredited third-party laboratories facilitate acceptance by overseas buyers and regulators
• Research and development, material comparison, supplier qualification, and failure analysis in laboratory and industrial settings

Test results from laboratories accredited to ISO/IEC 17025 carry particular weight in supplier approvals, tender submissions, and dispute resolution, because the technical competence of the laboratory has been independently confirmed.

FAQ

What is the difference between GB and GB/T standards?

GB standards are mandatory national technical regulations, while GB/T standards are recommended national standards. Breaking strength test methods are published as GB/T documents, but their requirements become obligatory when referenced by mandatory product codes, laws, or contractual specifications.

When should the strip method be used instead of the grab method?

The strip method measures the strength of a defined 50 mm fabric width and gives precise force-per-width data, making it suitable for most woven apparel fabrics. The grab method concentrates stress in the gripped central region and is preferred for coated, high-strength, or heavily constructed fabrics where raveling or jaw damage is a concern.

Which method applies to knitted fabrics?

Knitted fabrics are normally assessed by bursting strength using the hydraulic method of GB/T 7742.1 or the steel ball method of GB/T 19976, because their high extensibility makes direct strip tensile testing prone to jaw breaks and slippage.

How many specimens are required for a standard test?

The strip and grab fabric methods require at least five valid specimens in each principal direction. Yarn testing normally requires a minimum of ten valid breaks per package, and additional specimens must be prepared whenever results are discarded due to jaw breaks or slippage.

What is the difference between breaking strength and tearing strength?

Breaking strength is the maximum force needed to rupture a specimen pulled in tension across its full width, while tearing strength measures the force required to propagate an existing cut or tear through the fabric. They are governed by different GB standards and describe different failure modes.

Are GB test results comparable with ISO and ASTM results?

Many GB breaking strength methods are adopted from or technically aligned with the corresponding ISO standards, such as GB/T 3923.1 with ISO 13934-1. Results are generally comparable when the same specimen geometry, gauge length, rate of extension, and conditioning are applied, though differences from ASTM procedures such as specimen width and speed should be considered when correlating data.

What happens if a specimen breaks inside the jaws?

If a specimen slips in the jaws or breaks within 5 mm of the jaw face and the result is abnormally low compared with the other values, the result is discarded and a replacement specimen is tested so the reported mean reflects genuine fabric strength.

Why is conditioning necessary before testing?

Textile mechanical properties are sensitive to temperature and moisture. Conditioning specimens in the standard atmosphere defined by GB/T 6529 ensures that the moisture content is in equilibrium, which makes results reproducible between laboratories and comparable over time.