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CAN CGSB 4.175-M91 Part 3 (2013): Tearing Strength of Textile Fabrics – Trapezoid Method
A comprehensive guide to the Canadian standard for measuring fabric tear resistance in quality control and compliance applications
The CAN CGSB 4.175-M91 Part 3 (2013) standard, developed by the Canadian General Standards Board (CGSB), specifies the trapezoid method for determining the tearing strength of textile fabrics. This method is widely adopted across the Canadian textile industry for quality control, material specification, and product certification. It provides a reproducible and practical procedure for assessing a fabric’s resistance to tear propagation, which is critical for end‑use performance in apparel, industrial textiles, geotextiles, and protective clothing. This article outlines the scope, key technical requirements, implementation considerations, and compliance notes for laboratories and manufacturers working with this standard.
Scope and Application
CAN CGSB 4.175-M91 Part 3 (2013) is applicable to most woven and nonwoven textile fabrics, including those that have been treated with finishes or coatings, provided the test specimen can be cut and clamped as specified. The trapezoid method measures the force required to continue a tear initiated by a cut, simulating real‑world tearing failure. The standard is not intended for very extensible fabrics such as knits, where the trapezoid shape may not produce a valid tear; for such materials, alternative methods (e.g., the tongue tear method of Part 4) are recommended.
The method is used to evaluate tear resistance in both the warp and weft directions. Results are expressed in Newtons (N) and can be compared across different fabrics when tested under the same conditioning and testing parameters. The standard is referenced in procurement specifications for military, safety, and commercial textile products.
Technical Requirements
The test procedure relies on a constant‑rate‑of‑extension (CRE) tensile testing machine equipped with a suitable load cell and flat-faced clamps. The table below summarizes the critical specimen dimensions and testing parameters as defined in the standard.
| Parameter | Requirement |
|---|---|
| Specimen shape | Trapezoid |
| Specimen length (parallel to direction of tear) | 100 mm ± 1 mm |
| Short side width | 25 mm ± 0.5 mm |
| Long side width | 50 mm ± 0.5 mm |
| Cut length and position | 15 mm ± 0.5 mm from short side, centered perpendicular to the fold |
| Gauge length (distance between clamps) | 25 mm ± 1 mm |
| Crosshead speed | 300 mm/min ± 10 mm/min |
| Number of specimens per direction | 5 (minimum); 10 if higher precision required |
| Conditioning atmosphere | 20 °C ± 2 °C, 65% RH ± 4% |
| Conditioning time | At least 24 hours |
Specimen Preparation
Each specimen is cut in a trapezoidal shape with the longer side corresponding to the direction of tear (warp or weft). A 15 mm slit is made at the center of the short side, perpendicular to the edge, to initiate the tear. The specimen is then folded and clamped so that the cut aligns with the gap between the clamps. The CRE machine applies a constant extension rate until the tear propagates across the specimen.
Calculation of Tearing Strength
The tearing strength is taken as the average force recorded over a defined tearing distance (e.g., from the first peak to the end of the tear). The standard specifies that only the force values after the initial peak caused by the cut initiation are used, eliminating the start‑up effect. Results are reported as the mean tearing strength in Newtons for each direction, along with the standard deviation and the number of specimens.
Implementation Highlights
Proper implementation of CAN CGSB 4.175-M91 Part 3 (2013) requires careful attention to specimen preparation, equipment calibration, and data handling. The following points are particularly important for achieving reproducible results.
Tip: Condition all fabric specimens in the standard atmosphere (20 °C ± 2 °C, 65% RH ± 4%) for at least 24 hours before testing. Even brief exposure to ambient laboratory conditions can shift moisture content and alter tearing behavior, especially for hydrophilic fibers such as cotton and rayon.
Use a CRE testing machine with a capacity such that the tearing force falls between 10% and 90% of the load cell’s rated capacity. Regular calibration of the load cell and crosshead speed is essential. Many laboratories integrate digital data acquisition systems that automatically calculate the average tearing force from the force‑extension curve, reducing operator error.
Warning: Ensure that the cut in the specimen is precisely perpendicular to the edge and centered. A misaligned cut may cause the tear to deviate from the intended direction, invalidating the test. Use a template or cutting die to maintain accuracy.
The trapezoid method is often chosen over the tongue or Elmendorf methods because it uses a simple CRE machine and can be performed in‑house without specialized pendulum testers. However, it is sensitive to the tightness of the fabric weave and the presence of coatings. For heavily coated or laminated fabrics, modifications may be necessary – consult the standard’s notes for guidance.
Compliance Benefit: Laboratories adhering to CAN CGSB 4.175-M91 Part 3 (2013) can demonstrate traceability to a recognized national standard. This simplifies qualification for government procurement contracts, product certification programs, and supply‑chain audits.
Compliance and Verification Notes
To be fully compliant with CAN CGSB 4.175-M91 Part 3 (2013), testing facilities should consider the following:
- Accreditation: While the standard itself does not mandate laboratory accreditation, it is good practice to operate under ISO/IEC 17025. Many procurements require accredited data.
- Reference materials: Use of a control fabric with known tear properties is recommended for periodic verification of the test setup and operator technique.
- Reporting: The test report must include the fabric identification, direction (warp/weft), number of specimens, individual tear forces, mean, standard deviation, conditioning parameters, and any deviations from the standard (e.g., if a coated fabric required a different specimen size).
- Precision and bias: The standard provides guidance on repeatability and reproducibility based on round‑robin trials. Laboratories should participate in proficiency testing programs to confirm their results are consistent with the industry benchmark.
Caution: Do not use a testing speed other than 300 mm/min unless expressly permitted by the material specification. Deviation from the specified crosshead speed can significantly alter the tearing force and invalidate comparisons with published data.
Frequently Asked Questions
Q: What is the main difference between the trapezoid method (CAN CGSB 4.175 Part 3) and the tongue or Elmendorf methods?
A: The trapezoid method uses a folded specimen with a single cut and a CRE tensile tester, making it suitable for routine QC when a universal testing machine is available. The tongue method (Part 4) uses two slits and a higher initial force, while the Elmendorf method (ISO 13937‑2, ASTM D1424) measures tear resistance using a pendulum tester. Each method produces different numerical values and is chosen based on the fabric type and end‑use requirements.
A: The trapezoid method uses a folded specimen with a single cut and a CRE tensile tester, making it suitable for routine QC when a universal testing machine is available. The tongue method (Part 4) uses two slits and a higher initial force, while the Elmendorf method (ISO 13937‑2, ASTM D1424) measures tear resistance using a pendulum tester. Each method produces different numerical values and is chosen based on the fabric type and end‑use requirements.
Q: Can this standard be applied to nonwoven fabrics?
A: Yes, the standard explicitly includes nonwoven textiles. However, for very lightweight or highly extensible nonwovens, the trapezoid shape may not tear in the intended direction, and the test may need to be supplemented with alternative methods (e.g., strip tear). Always confirm the applicability with the relevant procurement specification.
A: Yes, the standard explicitly includes nonwoven textiles. However, for very lightweight or highly extensible nonwovens, the trapezoid shape may not tear in the intended direction, and the test may need to be supplemented with alternative methods (e.g., strip tear). Always confirm the applicability with the relevant procurement specification.
Q: How many specimens are required for a statistically valid test?
A: A minimum of five specimens in each direction (warp and weft) is required. For higher precision, especially for materials with high variability, ten specimens per direction are recommended. The standard deviation should be reported alongside the mean to assess variability.
A: A minimum of five specimens in each direction (warp and weft) is required. For higher precision, especially for materials with high variability, ten specimens per direction are recommended. The standard deviation should be reported alongside the mean to assess variability.
Q: Is it permissible to test fabrics that have been wet or washed?
A: The standard specifies testing in the conditioned state (dry). If wet or washed fabrics are to be tested (e.g., for wet tear strength), the procedure must be followed with appropriate modifications, and those deviations must be clearly noted in the report. Additional conditioning in water and testing within a specified time may be required.
A: The standard specifies testing in the conditioned state (dry). If wet or washed fabrics are to be tested (e.g., for wet tear strength), the procedure must be followed with appropriate modifications, and those deviations must be clearly noted in the report. Additional conditioning in water and testing within a specified time may be required.
This technical article was prepared in 2026 to support industry understanding of CAN CGSB 4.175-M91 Part 3 (2013). For the most current information, always refer to the official CGSB publication.