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CAN CGSB 4.2 No. 4.5-M86 (2013): Standard Test Method for Breaking Strength of Fabrics (Strip Method) with CRT Equipment
A Comprehensive Guide to the Canadian Standard for Tensile Testing of Textile Fabrics
Scope and Application
CAN CGSB 4.2 No. 4.5-M86 (2013) is a Canadian national standard developed by the Canadian General Standards Board (CGSB). It specifies a procedure for determining the breaking strength and elongation of woven textile fabrics using a constant-rate-of-traverse (CRT) tensile testing machine when tested by the strip method. This standard applies to most woven fabrics, including those that are bleached, dyed, printed, or otherwise finished, and may also be used for nonwoven and knitted fabrics where appropriate.
The strip method involves cutting test specimens to a specific width and raveling the opposite sides to achieve a known number of yarns in the test width, ensuring that failure occurs predominantly due to yarn breakage rather than yarn slippage. This method is widely employed in textile quality control laboratories and material acceptance testing for industries such as apparel, automotive textiles, geotextiles, and industrial fabrics.
Tip: The strip method is generally preferred over the grab method for fabrics that are prone to yarn slippage at the edges, as the frayed edges eliminate edge effects and provide a more accurate measure of yarn strength.
Technical Requirements and Test Method
Testing Equipment
The standard mandates the use of a constant-rate-of-traverse (CRT) tensile testing machine, where the pulling clamp moves at a constant speed while the force is measured. The machine must meet the following criteria:
- Capacity range such that the breaking force falls between 10% and 90% of the full-scale load.
- Accuracy within ±1% of the indicated load.
- Constant rate of traverse: the moving clamp travels at a uniform speed of 300 ± 10 mm/min or as specified in the product standard.
- Clamps shall have smooth, flat gripping surfaces (e.g., rubber‑faced or serrated) to prevent slippage without damaging the specimen.
Specimen Preparation
Test specimens are cut to a width of 50 ± 0.5 mm and a length sufficient to allow for raveling and clamping. The specimen is then raveled (i.e., yarns are removed from each side) until the remaining width is exactly 50 mm, containing a known number of yarns. The following table summarizes the standard specimen dimensions:
| Parameter | Requirement |
|---|---|
| Specimen nominal width (pre‑ravel) | 50 mm ± 0.5 mm |
| Specimen length (minimum) | 200 mm (to allow adequate clamp separation) |
| Gauge length (distance between clamps at start) | 75 mm ± 1 mm |
| Number of specimens per direction (warp and weft) | 5 minimum (10 recommended for higher precision) |
| Conditioning atmosphere | 20 ± 2 °C, 65 ± 4% RH (specimens conditioned for at least 24 hours) |
Important: For fabrics that cannot be raveled without fraying the yarns (e.g., nonwovens or certain knits), the standard allows the use of a modified procedure with a raveled width of 25 mm or a cut width of 50 mm without raveling, provided that such deviations are reported.
Test Procedure
- Condition the specimens in the standard atmosphere for at least 24 hours.
- Set the gauge length to 75 mm and the speed of the moving clamp to 300 ± 10 mm/min.
- Mount the specimen centrally in the clamps, taking care to avoid any tension or slack.
- Start the machine and record the breaking force (in newtons or kilogram-force) and elongation (in mm or percentage) at the moment of rupture.
- Discard results if the break occurs within 5 mm of the clamp edge; repeat the test.
- Calculate the average breaking strength and elongation for each direction.
Expression of Results
Results are reported as the arithmetic mean of the individual breaking strengths (in N or kgf) or as breaking force per unit width (e.g., N/cm). Elongation is expressed as a percentage of the original gauge length. The report must also include the coefficient of variation and the number of specimens tested.
Best Practice: When breaking strength is used for fabric acceptance, the standard recommends testing both warp (machine direction) and weft (cross direction) and reporting them separately, along with the fabric mass per unit area for context.
Implementation and Key Considerations
Selection of Test Method
CAN CGSB 4.2 No. 4.5-M86 uses the strip method, which differs from the grab method (CAN CGSB 4.2 No. 4.4-M86). The strip method tests the full width of the specimen (50 mm of yarns), making it more representative of the fabric’s tensile behavior when stressed in a narrow band. It is particularly suitable for fabrics where yarn interlock may cause premature failure in grab tests.
Equipment Calibration and Maintenance
- CRT machines must be calibrated annually or after any load cell replacement.
- Clamp pressure should be uniform and checked regularly to avoid sample slipping or jaw breaks.
- Speed verification should be performed using a stopwatch or tachometer.
Common Pitfalls
- Jaw breaks: If the fabric breaks directly at the clamp edge, the result may not reflect true yarn strength – increase clamp pressure or use padding.
- Non‑uniform raveling: Inconsistent removal of yarns can lead to variable widths and inaccurate results – use a template or tearing force to ensure a straight edge.
- Conditioning errors: Fabrics are hygroscopic; insufficient conditioning can shift results by 5–10%.
Warning: Failure to condition fabric specimens per the standard can lead to significantly erroneous breaking strength values, as moisture content directly affects yarn tenacity. Always condition for a minimum of 24 hours in controlled atmosphere (20 ± 2 °C, 65 ± 4% RH).
Compliance and Quality Assurance Notes
Organizations using CAN CGSB 4.2 No. 4.5-M86 must ensure the following for compliance:
- Accreditation: Testing laboratories should be accredited by a recognized body (e.g., SCC, A2LA) for this method.
- Documentation: All deviations from the standard (e.g., different specimen size, non‑standard speed) must be recorded and reported.
- Interlaboratory comparisons: Regular proficiency testing is recommended to reduce between‑lab variability, which for breaking strength can be as high as 10–15%.
- Review cycle: This standard was reaffirmed in 2013; users should verify if a newer edition has been published by CGSB or if ASTM D5035 is applied as an alternative for international trade.
The standard is referenced in many Canadian procurement specifications for textiles, including those for government uniforms, protective clothing, and industrial fabrics. It aligns closely with ASTM D5035 (Standard Test Method for Breaking Force and Elongation of Textile Fabrics (Strip Method)), with minor editorial differences. For manufacturers exporting to Canada, demonstrating compliance with this CGSB standard may be a contractual requirement.
Tip: For manufacturers who also need to satisfy international markets, consider cross‑referencing CAN CGSB 4.2 No. 4.5‑M86 with ISO 13934‑1 (strip method) to streamline testing schedules, as the principles and specimen dimensions are very similar.
Frequently Asked Questions
Q: What is the main difference between CAN CGSB 4.2 No. 4.5-M86 and the grab method (CAN CGSB 4.2 No. 4.4-M86)?
A: In the strip method, the test width is reduced by raveling the sides until only 50 mm of yarns remain, so the entire force is carried by these yarns. The grab method uses a wider specimen but only a central 25 mm portion is gripped, introducing a biaxial stress state that can give lower strength values for some fabrics. The strip method generally yields higher and more reliable results for tightly woven constructions.
A: In the strip method, the test width is reduced by raveling the sides until only 50 mm of yarns remain, so the entire force is carried by these yarns. The grab method uses a wider specimen but only a central 25 mm portion is gripped, introducing a biaxial stress state that can give lower strength values for some fabrics. The strip method generally yields higher and more reliable results for tightly woven constructions.
Q: Can this standard be used for knitted or nonwoven fabrics?
A: The standard is written specifically for woven fabrics, but it notes that it may be adapted for other fabric types with suitable modifications (e.g., using a cut width of 50 mm without raveling). However, specialized methods like ISO 9073-3 (nonwovens) or ASTM D5034 (knits) may be more appropriate. Always check with the relevant product specification.
A: The standard is written specifically for woven fabrics, but it notes that it may be adapted for other fabric types with suitable modifications (e.g., using a cut width of 50 mm without raveling). However, specialized methods like ISO 9073-3 (nonwovens) or ASTM D5034 (knits) may be more appropriate. Always check with the relevant product specification.
Q: How should I interpret the elongation results from this test?
A: The elongation at break is measured between the clamp grips at the moment of rupture. It includes both the true yarn extension and any clamping slippage. To isolate yarn stiffness, some users mark a gauge length directly on the fabric and measure elongation using an extensometer. The standard allows for this but requires reporting the method used. Typical elongation for woven cotton is 10–25% in warp direction and 15–35% in weft.
A: The elongation at break is measured between the clamp grips at the moment of rupture. It includes both the true yarn extension and any clamping slippage. To isolate yarn stiffness, some users mark a gauge length directly on the fabric and measure elongation using an extensometer. The standard allows for this but requires reporting the method used. Typical elongation for woven cotton is 10–25% in warp direction and 15–35% in weft.
Q: Is CAN CGSB 4.2 No. 4.5-M86 equivalent to ASTM D5035?
A: Yes, they are technically equivalent. ASTM D5035 (formerly ASTM D1682) was the original source for the Canadian standard. The current edition of CGSB 4.2 No. 4.5-M86 (reaffirmed 2013) mirrors the ASTM method, though minor editorial differences may exist. For most practical purposes, the two methods can be used interchangeably, but mandatory compliance with the CGSB version is required when specified in Canadian contracts.
A: Yes, they are technically equivalent. ASTM D5035 (formerly ASTM D1682) was the original source for the Canadian standard. The current edition of CGSB 4.2 No. 4.5-M86 (reaffirmed 2013) mirrors the ASTM method, though minor editorial differences may exist. For most practical purposes, the two methods can be used interchangeably, but mandatory compliance with the CGSB version is required when specified in Canadian contracts.