Pendulum Impact (Elmendorf) Tearing Strength Test – Technical Guide to Fabric Tear Resistance Measur

The pendulum impact tearing strength test, commonly known as the Elmendorf method, is a globally recognized technique for measuring the tear resistance of woven fabrics, nonwovens, and coated textiles. Performed in accordance with ISO 13937-1, ASTM D1424, and GB/T 3917.1, this test quantifies the force required to propagate a tear through a pre-cut specimen using a falling ballistic pendulum. This article provides a complete technical overview covering testing principles, specimen requirements, procedures, result interpretation, and typical industrial applications.

Technical Overview

The pendulum impact tearing strength test is a high-speed tearing method that determines the resistance of a fabric to tear propagation. A rectangular specimen with a predefined slit is clamped between a fixed jaw and a movable jaw attached to a ballistic pendulum. When the pendulum is released from its raised position, it swings downward under gravity, and the energy transferred through the moving clamp propagates the tear along the length of the specimen. The energy absorbed during tearing is converted into a tear force value, typically expressed in newtons (N), millinewtons (mN), or gram-force (gf), depending on the instrument configuration.

The method is fundamentally different from slow-speed tearing methods such as the trouser test or wing test, because tearing occurs at a high propagation speed that more closely simulates sudden snagging or burst-type failures in real-world use. This dynamic character makes the pendulum method the preferred quality-control instrument for production monitoring, incoming material inspection, and conformity assessment of textile products in accredited third-party laboratories.

The principal standards governing this method include:

• ISO 13937-1 – Textiles – Tear properties of fabrics – Determination of tear force using ballistic pendulum method (Elmendorf)
• ASTM D1424 – Standard Test Method for Tearing Strength of Fabrics by Pendulum (Elmendorf-Type) Apparatus
• GB/T 3917.1 – Textiles – Tear properties of fabrics – Part 1: Determination of tear force by ballistic pendulum method
• ISO 139 – Textiles – Standard atmospheres for conditioning and testing (for specimen conditioning)

Testing Samples

Woven Fabrics

Conventional woven fabrics in both warp and weft directions are the primary application of this method. Typical substrates include cotton, polyester, nylon, and blended shirtings, uniform fabrics, workwear, pocketing, canvas, and industrial woven textiles. Both directions of the fabric are evaluated separately because tear resistance is strongly anisotropic.

Nonwoven Fabrics

Spunbond, meltblown, needle-punched, hydroentangled, and thermally bonded nonwovens can be tested, provided the material is sufficiently rigid to be clamped and torn cleanly along the slit direction. The method is widely used for medical protective materials, interlinings, filtration media, and geotextile-facing layers.

Coated, Laminated, and Treated Fabrics

Coated fabrics (PVC, PU, rubber), laminated textiles, and fabrics finished with resin or durable press treatments are frequently evaluated, since coating and crosslinking finishes often reduce tear propagation resistance. This test quantifies such effects.

Materials Not Recommended

• Highly elastic knitted fabrics, where clamp slippage and elongation invalidate results
• Loose open-weave structures that tear in an uncontrolled zig-zag path
• Very heavy industrial fabrics exceeding the maximum pendulum capacity, which require alternative methods such as the trouser tear test

Testing Items

The pendulum impact method delivers the following measurable outcomes:

• Mean tear force in the length (warp) direction, expressed in N
• Mean tear force in the width (weft) direction, expressed in N
• Maximum and minimum single-specimen tear force values for variability assessment
• Coefficient of variation (CV) of tear force, indicating fabric uniformity
• Statistical validity checks, including detection of outliers and verification of normal distribution per standard requirements
• Optional supplementary values such as tearing work or tear resistance in gf for legacy instrument comparison

Results are reported separately for each fabric direction and each face of the fabric if orientation is known to influence tearing behavior. Acceptance limits, where applicable, are defined by product specifications, purchase contracts, or regulatory requirements.

Testing Methods

Principle of Measurement

The instrument measures the potential energy lost by the pendulum as it tears the specimen over a fixed tearing distance (43 mm in ISO 13937-1 and ASTM D1424). Because the tearing distance is constant, the average tear force is directly proportional to the absorbed energy. Digital instruments integrate the force-displacement response during tearing; mechanical instruments use a graduated scale and pendulum-specific conversion factors.

Specimen Preparation

• Cut rectangular specimens with dimensions specified by the applicable standard (typically 100 mm × 63 mm for ISO 13937-1; 100 mm × 75 mm for ASTM D1424)
• Prepare at least five specimens per direction, sampled diagonally across the fabric width to represent the full lot, with no two specimens containing the same warp or weft yarns
• Mark specimens clearly to identify fabric direction and laboratory face
• Condition specimens in the standard atmosphere of 20 °C ± 2 °C and 65 % ± 4 % relative humidity (ISO) or 21 °C ± 1 °C and 65 % ± 2 % relative humidity (ASTM) until moisture equilibrium is reached

Instrument Setup and Calibration

• Select a pendulum capacity so that the measured tear force falls between approximately 15 % and 85 % of full-scale range for mechanical types, or within the validated range of the sensor for digital types
• Verify zero setting by performing a blank swing without a specimen; the residual reading must fall within the tolerance defined by the standard
• Confirm the tearing knife condition and slit depth (20 mm) before each test series
• Calibrate and verify the apparatus at documented intervals using certified reference specimens

Test Procedure

• Raise the pendulum to the locked starting position and verify the pointer or electronic zero
• Clamp the specimen in the two jaws, ensuring it is centered, free of tension distortion, and aligned with the tear path
• Actuate the built-in knife to initiate the 20 mm slit, taking care not to cut beyond the specified depth
• Release the pendulum; the moving jaw carries one side of the specimen away while the fixed jaw holds the other, propagating the tear through the remaining specimen width
• Record the tear force indicated by the scale or electronic display
• Repeat for all specimens in each direction, replacing the specimen after each complete test

Calculation and Reporting

• Convert scale readings to force units using the pendulum factor where applicable
• Calculate the arithmetic mean tear force for each direction from valid specimens
• Evaluate the coefficient of variation; if it exceeds the limit specified in the standard, perform statistical outlier checks and test additional specimens as required
• Report the standard used, conditioning atmosphere, pendulum capacity, number of specimens, individual values, mean tear force per direction, and any deviations

Key Influence Factors

• Yarn mobility within the fabric structure – fabrics that allow yarn bunching at the tear tip show higher tear force
• Finishing chemistry – resin and durable-press finishes typically reduce tear strength by restricting yarn movement
• Coating weight and penetration – heavier coating generally decreases tear propagation resistance
• Conditioning state – moisture content significantly affects hydrophilic fibers such as cotton and viscose
• Specimen alignment and slit quality – misalignment or an improper slit produces biased or invalid results

Applications

The pendulum impact tearing strength test is applied across the entire textile value chain for quality control, product development, and conformity verification:

• Apparel and workwear – verifying that shirtings, uniforms, protective clothing, and denim resist snag-induced tearing during service
• Military and public safety textiles – qualifying combat uniforms, tactical gear, and flame-resistant fabrics against strict tear specifications
• Technical and industrial textiles – evaluating filter fabrics, conveyor belt fabrics, tarpaulins, and coating substrates
• Home textiles – assessing upholstery, curtain, and bedding fabrics for durability claims
• Medical and hygiene nonwovens – confirming tear performance of surgical gowns, drapes, and disposable protective materials
• Fabric development and finish optimization – comparing resin, softener, and coating formulations by their effect on tear propagation
• Dispute resolution and regulatory compliance – generating internationally recognized test reports through accredited third-party laboratories for buyers, retailers, and customs authorities

FAQ

What is the difference between the pendulum method and the trouser tear method?

The pendulum (Elmendorf) method tears the specimen dynamically at high speed and reports an average force derived from absorbed energy, while the trouser method (ISO 13937-2) tears the specimen at a slow constant rate on a tensile tester and reports peak-force statistics. The pendulum method is faster and better suited to routine quality control; the trouser method offers greater insight into tearing mechanics.

Which standard should I choose: ISO 13937-1, ASTM D1424, or GB/T 3917.1?

The three standards are technically harmonized and use the same ballistic pendulum principle, but they differ in specimen dimensions, conditioning atmosphere, and reporting details. The choice depends on the destination market and the contractual specification: ISO and EN markets typically reference ISO 13937-1, North American buyers commonly specify ASTM D1424, and GB/T 3917.1 governs conformity in the Chinese domestic market.

Why are five specimens tested in each direction?

Tear force is inherently variable because it depends on local yarn spacing, finish distribution, and structural irregularities. Testing five specimens per direction, sampled across the fabric width, provides a statistically defensible mean value and allows variability to be assessed, as required by the standards.

Can knitted fabrics be tested by this method?

Knitted fabrics are generally not suitable because their high extensibility causes slippage in the clamps and unstable tear paths. Alternative evaluations, such as burst strength or dedicated knit-tear procedures, are recommended for elastic structures.

How are abnormal results handled?

Specimens that slip in the clamps, tear outside the designated path, or produce readings outside the pendulum range are rejected and replaced. The standards also prescribe statistical procedures for identifying outliers when the coefficient of variation is high, ensuring the reported mean reflects genuine fabric performance.

What tear force values are considered acceptable?

There is no universal pass threshold; acceptance limits depend on the end use, product standard, and buyer specification. For example, workwear and military fabrics commonly require higher minimum tear force than lightweight apparel fabrics. The laboratory reports measured values against the limit defined in the applicable specification.