Geomagnetic fabric breaking strength testing is a fundamental textile performance evaluation that measures the maximum tensile force a functional geomagnetic fabric can withstand before rupture in the warp and weft directions. This testing is typically performed in accredited third-party laboratories in accordance with internationally recognized standards such as ISO 13934-1, ISO 13934-2, GB/T 3923.1, GB/T 3923.2, ASTM D5035 and ASTM D5034. Understanding the testing procedure, sample requirements and result interpretation helps manufacturers, brands and buyers ensure the durability, safety and compliance of geomagnetic textile products.
Technical Overview
Geomagnetic fabric is a category of functional textile that incorporates magnetic components—such as magnetic fibers, ferrite-based particles, magnetically responsive coatings or laminated magnetic films—into a woven, knitted or composite fabric structure. These fabrics are used in health-care textiles, electromagnetic shielding products, industrial filtration and other technical applications. Because the incorporation of magnetic fillers, coatings and composite layers can alter yarn mobility, coating adhesion and overall tensile behavior, breaking strength is one of the most critical quality indicators for this material class.
Breaking strength (also referred to as breaking force or tensile breaking strength) is defined as the maximum force, expressed in newtons (N), that a fabric specimen can resist before rupturing under uniaxial tensile loading. The test is normally performed on a constant-rate-of-extension (CRE) tensile testing machine, with specimens tested in both the lengthwise (warp) and widthwise (weft) directions. In addition to breaking force, the test yields breaking elongation, which reflects the deformation capacity of the fabric at rupture.
The principal standards governing geomagnetic fabric breaking strength testing include:
- ISO 13934-1 / EN 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 / EN ISO 13934-2 — Part 2: determination of maximum force using the grab method.
- GB/T 3923.1 — Chinese national standard for the strip method, technically aligned with ISO 13934-1.
- GB/T 3923.2 — Chinese national standard for the grab method, technically aligned with ISO 13934-2.
- ASTM D5035 — Standard test method for breaking force and elongation of textile fabrics (strip method).
- ASTM D5034 — Standard test method for breaking strength and elongation of textile fabrics (grab method).
- ISO 13935-1 / ISO 13935-2 — Determination of seam maximum force using strip and grab procedures, applicable when seam strength evaluation is required.
Testing Samples
Woven Geomagnetic Fabrics
Woven geomagnetic fabrics—produced by interlacing magnetic-blended or coated warp and weft yarns—are the most common sample type for breaking strength testing. Representative samples should be taken from full-width fabric at least one meter away from the roll end, avoiding selvedges, creased areas, folds and visibly defective zones. Specimens are cut with the long dimension parallel to either the warp or weft direction, and the direction must be clearly marked before testing.
Knitted Magnetic Fabrics
Knitted structures containing magnetic fibers or functional coatings generally exhibit lower breaking strength but higher elongation than wovens. Due to their high elasticity, knitted geomagnetic fabrics may require modified gauge lengths or the use of applicable knitted-fabric procedures, and results should be interpreted with reference to the fabric's intended end use.
Coated, Laminated and Composite Fabrics
Many geomagnetic fabrics are produced by coating or laminating a magnetic functional layer onto a base fabric. Coating thickness, binder content and laminating pressure all influence tensile performance. Specimens from coated fabrics should be conditioned and tested flat, without stretching, folding or pre-damage, so that the reported strength reflects the true composite performance.
Finished Products and Laboratory Swatches
Testing may be performed on swatches cut from finished products such as magnetic therapy wraps, shielding curtains, mattress covers or industrial rolls, provided the sampled area is sufficiently large and free from seams unless seam strength itself is the test object. A typical laboratory submission consists of several pieces of fabric of approximately 350 mm in length across the full usable width, or equivalent material allowing at least five valid specimens per direction.
Testing Items
A complete breaking strength evaluation of geomagnetic fabric typically includes the following measured and calculated parameters:
- Breaking strength (maximum force) in the warp direction, expressed in N.
- Breaking strength (maximum force) in the weft direction, expressed in N.
- Breaking elongation and elongation at maximum force, expressed in %.
- Elongation at a specified force, where required for engineering or product design purposes.
- Breaking tenacity or strength-to-weight indicators, where fabric mass per unit area is also determined.
- Seam breaking strength and seam slippage resistance, where the fabric is assembled with stitches in the final product.
- Statistical treatment of results: individual values, arithmetic mean, coefficient of variation, and minimum value per direction.
For functional geomagnetic fabrics, breaking strength is frequently evaluated both in the original state and after durability treatments such as domestic or commercial laundering (for example using ISO 6330 or GB/T 8629 washing procedures), dry cleaning, abrasion, or accelerated aging, in order to characterize strength retention over the product life cycle.
Testing Methods
Specimen Preparation and Conditioning
All specimens are conditioned in a standard atmosphere of (20 ± 2) °C and (65 ± 4) % relative humidity in accordance with ISO 139 or GB/T 6529 for a minimum of 24 hours, or until moisture equilibrium is reached. For each fabric direction, at least five valid specimens are prepared, cut from positions distributed across the full fabric width so that no two specimens contain the same set of lengthwise yarns. Specimens must be free of wrinkles, creases and manufacturing defects.
Strip Method
In the strip method (ISO 13934-1, GB/T 3923.1, ASTM D5035), a rectangular specimen of 50 mm effective width and adequate length for a 200 mm gauge length is clamped in the upper and lower jaws of a CRE tensile tester. An appropriate pre-tension is applied according to the fabric mass per unit area—for example 2 N for fabrics not exceeding 200 g/m², 5 N for fabrics between 200 g/m² and 500 g/m², and 10 N for fabrics above 500 g/m². The rate of extension is normally 20 mm/min for fabrics with elongation below 75 % at maximum force. The machine is started and extended until the specimen ruptures; the maximum force recorded before rupture is taken as the breaking strength, and the corresponding elongation is reported. Specimens that break within the jaws or slip noticeably are rejected and replacement specimens are tested.
Grab Method
In the grab method (ISO 13934-2, GB/T 3923.2, ASTM D5034), a wider specimen—typically 100 mm wide with a central gripping zone of 25 mm × 25 mm jaw faces and a gauge length of 100 mm—is extended at a rate of 100 mm/min until rupture. The grab method is particularly suitable for high-strength, coated or densely woven geomagnetic fabrics, for fabrics where raveling of specimens is difficult, and when results closer to real-world fabric performance are required, because the stress is concentrated in the central gripped width. The maximum force sustained is reported as the grabbing breaking strength.
Equipment and Calibration
Testing is conducted on a calibrated constant-rate-of-extension tensile testing machine meeting the force-verification requirements of ISO 7500-1, with force sensors and extension indicators of suitable accuracy and capacity matched to the expected strength range of the geomagnetic fabric. Jaws must hold the specimen without slipping; pneumatic or padded grips are commonly used for coated and slippery fabrics. Regular calibration, capability verification and inter-laboratory validation ensure traceable and reproducible results.
Calculation and Reporting
The breaking strength of each valid specimen is read directly in newtons, and the arithmetic mean is calculated for each direction, rounded according to the standard. The test report should identify the standard applied, the test method (strip or grab), machine type, gauge length, rate of extension, conditioning atmosphere, number of specimens, individual and mean results with coefficient of variation, observations of jaw breaks or slippage, and any deviations from the standard procedure.
Applications
Geomagnetic fabric breaking strength testing serves multiple purposes across the product development and supply chain:
- Research and development: evaluating how magnetic fiber content, filler loading, coating formulation and finishing processes affect tensile performance, guiding formulation and structure optimization.
- Incoming quality control: verifying that delivered fabric batches meet contractual strength specifications before production.
- Product certification and compliance: demonstrating conformity with national and international product standards for functional and health-care textiles.
- Durability and life-cycle assessment: measuring strength retention after repeated laundering, abrasion, humidity and UV exposure to substantiate durability claims.
- Supplier comparison and trade settlement: providing objective, accredited third-party laboratory data for buyer–supplier agreements and dispute resolution.
- Failure analysis: diagnosing the causes of fabric rupture, delamination or premature degradation in service.
FAQ
What is the difference between the strip method and the grab method?
The strip method measures the strength of the full specimen width with all yarns across the 50 mm width clamped and loaded, providing a result suitable for yarn strength characterization and comparison. The grab method grips only the central 25 mm portion of a wider specimen, allowing adjacent yarns to contribute to load transfer, and often better reflects actual fabric performance, especially for coated, high-strength or difficult-to-ravel fabrics. The choice of method should follow the product standard or the agreement between buyer and supplier.
How many specimens are required, and what sample quantity should be submitted?
A minimum of five valid specimens is required for each fabric direction under ISO and GB procedures, meaning at least ten specimens in total for warp and weft. In practice, laboratories recommend submitting enough fabric to cut additional replacement specimens—for example, several full-width pieces of at least 350 mm length—to account for rejected results caused by jaw breaks or slippage.
Why do warp and weft results differ on the same fabric?
Warp and weft yarns commonly differ in twist, count, density and the stresses introduced during weaving, coating or laminating. It is normal for geomagnetic fabrics to show asymmetric strength between directions, and product specifications typically define separate minimum requirements for each.
What happens if a specimen breaks in the jaws or slips during testing?
Specimens that rupture within 5 mm of the jaw line or that slip visibly are considered invalid under the standards. Such results are discarded and additional specimens are tested until the required number of valid results is obtained; all observations are noted in the test report.
Can breaking strength be tested after washing or aging?
Yes. It is common practice to condition geomagnetic fabric specimens through repeated laundering cycles, dry cleaning, artificial weathering or abrasion prior to tensile testing, in order to evaluate strength retention and confirm long-term functional durability of the magnetic coating or filler system.
What information does the final test report contain?
An accredited third-party laboratory report includes sample identification, the applied test standard and method, conditioning details, machine parameters, individual and mean breaking strength values with elongation for each direction, statistical indicators, observations of invalid specimens, and a clear conformity statement against the specified acceptance criteria when these are provided by the client.