Double tongue method tear strength testing measures a fabric's resistance to tear propagation using a double-slit "tongue" specimen tested on a constant-rate-of-extension tensile machine, in accordance with ISO 13937-4 and GB/T 3917.4. This article explains the test principle, specimen preparation, equipment requirements, step-by-step procedure, result calculation, and typical applications, serving as a practical reference for textile manufacturers, quality engineers, and sourcing professionals.
Technical Overview
Tear strength, or tearing force, describes the ability of a fabric to resist the propagation of an existing cut or tear. Unlike tensile strength, which measures the force needed to break a fully gripped strip of fabric, tear testing measures the localized, sequential rupture of individual yarns along a tear line. Because fabrics in service frequently fail by tearing (snagging, puncturing, cut edges propagating under load), tearing force is one of the most important mechanical performance indicators for woven and coated textiles.
In the double tongue method, also known as the tongue test with double tear, a rectangular specimen is prepared with two parallel slits cut into one end, forming a central "tongue" of fabric. The central tongue is gripped in the movable clamp of a constant-rate-of-extension (CRE) tensile testing machine, while the two side panels are folded together and gripped in the fixed clamp. As the clamps separate, tearing proceeds simultaneously along both edges of the tongue, producing a characteristic force-extension curve with multiple peaks. The statistical evaluation of these peak forces gives the tearing force of the fabric.
The principal standards governing this method are ISO 13937-4 (Textiles – Tear properties of fabrics – Part 4: Determination of tear force by tongue test, double tear) and its national adoptions such as GB/T 3917.4 in China and EN ISO 13937-4 in Europe. ASTM D2262 historically described a similar tongue (double rip) procedure for CRE machines but has been withdrawn; the current ASTM counterpart for the related trouser (single rip) procedure is ASTM D2261. The double tongue method belongs to the same family of tear tests as the pendulum (Elmendorf) method (ISO 13937-1), the trouser method (ISO 13937-2), and the wing rip method (ISO 13937-3), each suited to different fabric types and end uses.
Testing Samples
Specimen Dimensions and Preparation
- Specimen size: 200 mm (length, in the tear direction) × 150 mm (width).
- Two parallel cuts, each 100 mm long, are made 50 mm apart from the mid-point of one short edge, forming a central tongue 50 mm wide and 100 mm long.
- To evaluate tearing in the warp direction, specimens are cut with the 200 mm length parallel to the warp yarns so the tear propagates along the warp; conversely for the weft direction. The yarns lying perpendicular to the tear path are the yarns that rupture.
- A minimum of five valid specimens is required for each direction, sampled well distributed across the full fabric width, avoiding the same set of lengthwise yarns, selvages, creases, and visible defects.
- Cuts must be clean and precisely aligned; frayed or angled cuts distort tear initiation and must be avoided.
Conditioning and Test Atmosphere
Specimens are conditioned to moisture equilibrium in the standard atmosphere of 20 °C ± 2 °C and 65 % ± 4 % relative humidity (or the tropical alternative of 27 °C ± 2 °C and 65 % ± 4 % relative humidity where applicable), typically for at least 24 hours, and tested in the same atmosphere. Pre-conditioning may be applied when the fabric's moisture history could affect results.
Material Suitability
The double tongue method is primarily intended for woven fabrics, including coated, laminated, and tightly woven technical fabrics. It is generally not suitable for knitted fabrics, highly elastic fabrics, or fabrics in which yarns slip rather than rupture under tear loading; for such materials, other tear methods (pendulum or trapezoid type) or strip tensile methods should be considered.
Testing Items
- Warp-direction tearing force, expressed in newtons (N).
- Weft-direction tearing force, expressed in newtons (N).
- Per-specimen tear force, determined as the median of the peak forces within the defined evaluation zone of the force-extension curve.
- Multi-specimen statistics for each direction, including the mean or median of valid results and the coefficient of variation.
- Qualitative tearing behavior: peak density and curve shape, yarn breakage versus yarn slippage, tear path deviation, and coating or lamination delamination during tearing.
Testing Methods
Apparatus
- A constant-rate-of-extension (CRE) tensile testing machine with force measurement accuracy within ±1 % and data acquisition fast enough to resolve individual tear peaks (typically 100 Hz or higher).
- Clamps with gripping faces wide enough for the specimen and sufficient, uniform grip pressure (pneumatic or screw action) to prevent specimen slippage; jaw liners may be used for delicate or coated fabrics.
- A sharp cutting die, template, blade, or scissors for specimen preparation; a steel rule and marking pen for slit positioning.
Test Procedure
- Set the initial gauge length between clamps to 100 mm and the rate of extension to 100 mm/min.
- Clamp the central tongue in the movable clamp, ensuring it is centered and free of twist.
- Fold the two side panels back on themselves, stack them together, and clamp them jointly in the fixed clamp, keeping the tongue perpendicular to the clamps with the specimen free of slack.
- Start the machine. The tear propagates simultaneously along both edges of the tongue; continue the test until the specified tear length (approximately 75 mm) is achieved or the specimen separates.
- Record the complete force-extension curve and extract the peak forces within the evaluation zone, excluding the initial and final few millimeters of tearing as specified by the standard.
- Repeat for all specimens in each direction and inspect each tested specimen for failure mode.
Invalid Tests and Retesting
- The tear deviates from the cut lines and runs to the edge of the specimen (tear transfer).
- The tongue ruptures at the jaw line, or the specimen slips in the clamps.
- The curve shows no distinguishable tearing peaks, for example a continuously rising force caused by yarn slippage rather than yarn rupture.
- Invalid specimens are discarded and replacements tested; all deviations and replacements are documented in the report.
Calculation and Expression of Results
For each valid specimen, the tear force is taken as the median of the peak forces within the evaluation zone, following the statistical treatment specified in ISO 13937-4. The reported result for each direction is derived from the valid specimens (mean or median as specified), together with the coefficient of variation. The test report should state the standard used, machine type, gauge length, speed, conditioning atmosphere, number and direction of specimens, individual and final results in newtons, and any observed anomalies such as tear deviation or slippage.
Applications
- Incoming inspection and batch conformity control of woven greige and finished fabrics in mills and garment supply chains.
- Performance verification of fabrics for workwear, military and tactical garments, outdoor and camping equipment, tents, sails, parachutes, upholstery, and medical and filtration textiles, where tear resistance is a safety-critical property.
- Research and development, including evaluation of fiber types, yarn and weave constructions, finishing and coating recipes, and laundering or aging effects on tear performance.
- Compliance testing against procurement specifications, product standards, and labeling claims, carried out by manufacturers or accredited third-party laboratories.
- Failure analysis of torn goods and investigation of customer claims or field failures.
Note that tear results obtained by different methods, such as pendulum, trouser, wing, trapezoid, and double tongue tests, are based on different geometries and force mechanisms and are not directly interchangeable. The method must always be agreed between the parties and stated with the result.
FAQ
What is the difference between the single tongue (trouser) and double tongue methods?
The trouser, or single tongue, method uses a specimen with a single central cut, so tearing propagates along one tear front. The double tongue method uses a specimen with two parallel cuts forming a central tongue, so tearing propagates simultaneously along two tear fronts. Because two tear lines are active at once, the double tongue test generally produces higher force readings and a different peak pattern, and the results of the two methods cannot be compared directly.
Which standards specify double tongue tear strength testing?
The governing standard is ISO 13937-4, which is adopted in China as GB/T 3917.4 and in Europe as EN ISO 13937-4. ASTM D2262 formerly covered an equivalent tongue (double rip) procedure but has been withdrawn; ASTM D2261 remains in use for the trouser (single rip) procedure.
How many specimens are required?
At least five valid specimens for each direction (warp and weft) are tested. Specimens should be taken from different positions across the fabric width so that no two specimens contain the same lengthwise yarns, and additional reserve specimens are recommended in case of invalid tests.
Why must invalid tests be repeated?
When the tear runs to the specimen edge, the tongue breaks at the jaw, or the specimen slips in the clamps, the recorded force no longer represents true double-tear propagation. Such results are statistically unrepresentative, so the specimen is discarded and a replacement is tested, with the event recorded in the report.
Can the method be used for knitted or stretch fabrics?
Generally no. In knits and elastic fabrics, tear loading is absorbed by loop deformation and yarn slippage rather than yarn rupture, so a stable tear path and meaningful peaks are not obtained. Alternative test methods should be selected for such materials.
What factors most influence the test result?
Key influences include the precision of the two slits, conditioning atmosphere, grip pressure and specimen alignment, tear propagation behavior of the fabric construction, and correct delimitation of the peak evaluation zone. Consistent machine settings and careful specimen preparation are essential for reproducible results.
How should results be reported?
Results are reported in newtons, typically as the median of the peak forces for each specimen and the mean or median of the valid specimens for each direction, together with the coefficient of variation, the applicable standard, test conditions, and any observations of abnormal tearing behavior.