Nonwoven fabric tearing strength testing measures the resistance of nonwoven materials to tear propagation, a critical durability parameter for medical protective apparel, hygiene products, filtration media, and geotextiles. This technical guide explains the trapezoid and Elmendorf test methods, the governing standards such as ISO 9073-4, ASTM D5733, and GB/T 24118, and best practices for specimen preparation, testing, and result interpretation. Whether you are performing incoming inspection or optimizing a bonding process, understanding tear testing helps ensure that nonwoven products maintain their integrity throughout conversion and end use.
Technical Overview
Tearing strength, also known as tear resistance, is defined as the force required to continue or propagate a tear that has been initiated by a deliberate cut or slit in a fabric under controlled test conditions. It is distinct from tensile strength, which measures the force needed to rupture an intact specimen under a gradually applied load. For nonwoven materials, tear performance is one of the most important mechanical quality indicators because nonwovens are frequently slit, cut, perforated, or sewn during conversion, and any notch or cut becomes a potential initiation point for tear propagation in service.
Nonwoven fabrics are engineered structures in which fibers or filaments are bonded together by mechanical entanglement, thermal bonding, or chemical adhesives rather than by interlacing yarns. Because of this anisotropic fiber architecture, tearing strength must be evaluated separately in the machine direction (MD, longitudinal) and the cross direction (CD, transverse). Depending on the web-forming process, values in the two directions can differ substantially, and product specifications commonly require minimum values in both.
During a tear test, the nonwoven fails through one or more mechanisms, and the dominant mechanism directly influences the measured force:
- Fiber or filament breakage at the tear tip, typical of strongly bonded structures.
- Fiber pull-out or slippage, common in lightly bonded or entangled webs, which dissipates energy and can raise tear resistance.
- Bond-point or adhesive-layer rupture, which produces characteristic force peaks in calendered and chemically bonded nonwovens.
Results are normally expressed in newtons (N), and depending on the method and specification, either the maximum (peak) tear force or the average of the sequential force peaks generated during propagation is reported.
Testing Samples
Tearing strength testing is applicable to virtually all commercial nonwoven categories. Specimens should be taken from representative, defect-free areas of the fabric, away from selvages, creases, and obvious local irregularities. Before testing, samples are conditioned in a standard atmosphere in accordance with ISO 139 (typically 20 ± 2 °C and 65 ± 4 % relative humidity) until moisture equilibrium is reached, normally no less than 24 hours, because moisture content can significantly influence the tear behavior of many fiber types.
Spunbond Nonwovens
Continuous-filament polypropylene or polyester spunbond fabrics used in medical packaging, protective apparel, and agricultural covers. These fabrics are usually tested in both MD and CD, and SMS (spunbond-meltblown-spunbond) composites are frequently evaluated as complete structures.
Meltblown Nonwovens
Ultrafine-fiber webs used as filtration layers, most notably in respiratory masks and liquid filtration media. Because their intrinsic tear strength is low, meltblown layers are often tested as part of a laminate to characterize the performance of the functional composite.
Spunlace (Hydroentangled) Nonwovens
Hydroentangled fabrics of polyester, viscose, or blended fibers used in medical gowns, wipes, and wet wipes. Their tear behavior is governed by fiber entanglement rather than thermal bond points, which makes tear testing particularly informative for process control.
Needle-Punched Nonwovens
Denser, thicker structures used in geotextiles, automotive interiors, carpet backing, and dust filtration. Needle-punched geotextiles are commonly specified with minimum tear strength requirements in both principal directions.
Thermally and Chemically Bonded Nonwovens
Calender-bonded or resin-bonded webs used in interlinings, roofing substrates, and hygiene components. Tear force traces typically show periodic peaks corresponding to successive bond-point failures.
Composite and Laminated Nonwovens
Multilayer constructions combining nonwoven layers with films, foams, or scrims. Testing is performed on the finished laminate, since the laminate tear strength, not that of the individual layers, determines product performance.
Testing Items
A standard nonwoven tearing strength test report typically includes the following measured and derived items:
- Machine direction (longitudinal) tearing strength, in N.
- Cross direction (transverse) tearing strength, in N.
- Maximum (peak) tear force for each specimen and the mean per direction.
- Average tearing force, calculated from the mean of the propagation force peaks where the applicable method requires it.
- Observations of tear path behavior, including deviations from the intended propagation line, fiber pull-out, or delamination in composites.
- Test method, standard applied, specimen dimensions, gauge length, speed, conditioning atmosphere, and number of specimens tested.
Testing Methods
Two principal methods are used for the tearing strength of nonwoven fabrics: the trapezoid method, which is generally regarded as the primary method for nonwovens, and the Elmendorf falling-pendulum method, which is widely used for lightweight fabrics.
Trapezoid Method (ISO 9073-4, ASTM D5733, GB/T 24118)
A rectangular specimen is marked with two lines defining a trapezoid, and a short initial slit (typically 15 mm) is cut at the center of the shorter side. The specimen is clamped along the two non-parallel trapezoid lines so that the sides are held taut on one edge and slack on the other, concentrating the stress at the tip of the slit. The jaws of a constant-rate-of-extension (CRE) tensile testing machine then separate at the speed specified by the standard (commonly 100 to 300 mm/min), and the tear propagates across the width of the specimen. The force-extension record yields either a single major peak or a sequence of peaks; the standard determines whether the maximum force or the average of the peaks is reported. A minimum of five valid specimens is normally tested in each direction, and specimens in which the tear runs off the edge or fails in the grips are discarded and replaced.
Elmendorf Falling-Pendulum Method (ASTM D5734 and Related Pendulum Standards)
In the pendulum procedure, a small rectangular specimen with a defined precut slit is clamped between a fixed jaw and a jaw mounted on a pendulum. When the pendulum is released, it swings down and tears the specimen along its remaining width. The energy lost by the pendulum is measured by a pointer on a graduated scale and is converted into tearing force using the instrument constant of the specific pendulum used. Testers are supplied with a range of pendulum capacities so that the measured tear energy remains within a reliable measurement window. The method is fast, requires only a small quantity of material, and is well suited to lightweight spunbond and spunlace nonwovens; it is also the reference method in the ISO 13937 and GB/T 3917 series for conventional textiles, which are frequently cross-referenced in nonwoven specifications.
Equipment, Calibration, and Test Conditions
Reliable results depend on properly maintained equipment and controlled conditions:
- A calibrated CRE tensile tester with an appropriately sized load cell, so that the tear force falls within the calibrated working range of the force-measuring system.
- Pneumatic or mechanical grips with parallel, non-slip faces; specimen slippage is a leading cause of invalid results.
- Sharp cutting dies and templates to produce specimens of accurate dimensions with clean, consistent slits, since the slit geometry directly controls where the tear initiates.
- Verification of pendulum capacity selection, pendulum zero position, and blade sharpness on Elmendorf instruments.
- Conditioning of all specimens in the standard atmosphere before testing, with testing carried out in the same atmosphere wherever practicable.
- Testing of at least five specimens per direction, reporting the mean, standard deviation, and coefficient of variation so that directional anisotropy and variability are visible.
Applications
Tearing strength data support design, specification, and quality control decisions across the entire nonwovens industry. Typical applications include:
- Medical and healthcare: surgical gowns, drapes, sterilization wraps, and face mask layers, where tear resistance is essential to maintaining barrier integrity during use. Performance-based specifications for surgical gowns and drapes, such as EN 13795, include minimum tear resistance requirements.
- Hygiene products: diaper backsheet layers, acquisition and distribution layers, sanitary products, and dry and wet wipes that must withstand tearing during dispensing and use.
- Filtration media: HVAC and cabin air filter substrates and bag filter fabrics, where tear strength ensures pleating, fabrication, and installation do not damage the medium.
- Geotextiles and construction: separation, filtration, and drainage layers in civil engineering, housewrap, and roofing underlayment, where tears caused by stones or fasteners must be resisted during and after installation.
- Automotive interiors: headliners, trunk liners, door trims, and acoustic insulation that must tolerate cutting, sewing, and long-term vibration.
- Packaging and agriculture: nonwoven shopping bags, crop covers, and weed-control fabrics exposed to handling loads and wind flutter.
- Quality control and R&D: incoming material inspection, supplier comparison, and process optimization, including calendering temperature and pressure, needling density, hydroentangling pressure, and binder add-on, all of which measurably influence tear strength.
In research and development, comparing MD and CD tear values before and after process changes provides a sensitive, low-cost indicator of how bonding energy is distributed through the web, often revealing changes in fabric hand and delamination tendency before they appear in other mechanical tests.
FAQ
Which test method should be used for nonwoven fabric tear testing?
The trapezoid method described in ISO 9073-4, ASTM D5733, and GB/T 24118 is the primary method for nonwovens because it reproduces the stress concentration at a cut edge and provides a full force-extension record. The Elmendorf pendulum method under ASTM D5734 is preferred for lightweight fabrics, for high-volume routine control, or when a customer specification explicitly requires it. When in doubt, the method should be agreed between supplier and purchaser and stated on the test report.
Why are machine direction and cross direction tear results different?
Nonwovens are anisotropic. Carded and parallel-laid webs have fibers preferentially oriented in the machine direction, so a tear running across the fibers encounters different resistance than one running along them. Spunbond and cross-lapped structures show their own characteristic orientation patterns. Reporting both directions is therefore standard practice, and product specifications almost always set separate minimum requirements for MD and CD.
How many specimens are required for a valid test?
Standards typically require a minimum of five valid specimens in each direction. Specimens whose tear deviates markedly from the intended path, runs off the specimen edge, or fails partially or completely in the grips are discarded and additional specimens are tested so that the reported mean is based on the required number of valid results.
What is the difference between maximum tear force and average tearing force?
The maximum tear force is the single highest force recorded during propagation, while the average tearing force is derived from the mean of the successive force peaks produced as the tear advances through successive bonding regions. The applicable standard and the product specification determine which value is reported, so the calculation basis should always be stated alongside the results.
What can be done if tear strength results are lower than the specification?
First, verify that testing is valid: correct standard, clean slit geometry, no grip slippage, adequate conditioning, and correct direction identification. If the test is valid, improvements usually come from the process side, including increasing bonding temperature, pressure, or dwell time, adjusting needling or hydroentangling energy, modifying binder add-on, blending stronger fiber types, or altering web layering to improve the weaker direction.
How should nonwoven tear test results be interpreted between laboratories?
Tear testing of nonwovens is sensitive to slit geometry, jaw alignment, speed, and conditioning, so interlaboratory differences are normal. Comparisons should only be made on the same test standard, same direction, same calculation basis, and ideally within the framework of interlaboratory verification using commonly accepted statistical comparison of the mean and coefficient of variation. Engaging accredited third-party laboratories for arbitration testing ensures that results are traceable to recognized standards.