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CAN CGSB 4.2 No. 9.2-M90 (2013): Breaking Strength of Fabrics – Grab Method
A comprehensive guide to Canada’s standard for determining the breaking strength of textile fabrics using the grab method
The CAN CGSB 4.2 No. 9.2-M90 (2013) standard, part of the Canadian General Standards Board (CGSB) 4.2 series on textile test methods, specifies the grab method for determining the breaking strength of textile fabrics. Originally published in 1990 and reaffirmed in 2013, this method is widely used by textile manufacturers, quality assurance laboratories, and regulatory bodies across Canada for evaluating the tensile properties of woven, nonwoven, and knitted fabrics. The grab method, unlike the strip test, tests a wider specimen width with only the central portion gripped, better simulating the stress distribution encountered in actual use.
Scope and Application
The standard applies to most textile fabrics, including those that are woven, nonwoven, felted, or knitted, provided the fabric can be reliably gripped without slippage. It covers both conditioned and wet testing. The method is intended for acceptance testing of commercial shipments and for quality control in manufacturing.
Tip: The grab method is particularly suited for fabrics that exhibit high stretch or where edge effects are significant. It is often preferred over the strip method for fabrics used in industrial applications, protective clothing, and geotextiles.
Applicability Limitations
- Fabrics that are excessively stretchable (e.g., some knits) may show jaw slippage or break at the grip edge; alternative methods like the modified grab test may be more appropriate.
- Very narrow fabrics (width less than the required specimen width) cannot be tested by this method.
Technical Requirements and Test Procedure
Apparatus
- Constant-rate-of-extension (CRE) tensile testing machine with a recording device.
- Grips: Smooth-faced, flat, metal grips, at least 25 mm wide and 25 mm in the direction of the load. Jaw faces may be plain or serrated; synthetic rubber facings are permitted to reduce slippage.
- Specimen cutter or template (100 ± 1 mm wide by 200 ± 1 mm long).
Specimen Preparation and Conditioning
Specimens are cut 100 mm wide and 200 mm long. For each test direction (warp/wale and filling/course), a minimum of five specimens are taken. The standard specifies that specimens be conditioned at 20 ± 2 °C and 65 ± 5 % relative humidity for at least 24 hours prior to testing. Wet testing requires immersing specimens in distilled or deionized water at 20 ± 2 °C for at least 1 hour.
Warning: Improper conditioning can lead to significant variability in breaking strength results. Always verify that the conditioning chamber meets the specified tolerances and that specimens are adequately exposed to the conditioned air.
Test Procedure
Each specimen is mounted centrally in the grips so that the jaws are 75 ± 1 mm apart. The width of the specimen is 100 mm, but only the central 25 mm (width of the jaw face) is actually gripped; the outer portions remain free. The machine is set to a constant rate of extension of 300 ± 10 mm/min (for CRE machines). The test is initiated, and the force at break (maximum force) is recorded in newtons or pounds-force.
Calculations
Report the average breaking strength for each direction (warp and filling, or machine and cross direction). The standard deviation and coefficient of variation may also be reported for precision analysis.
| Parameter | Requirement | Notes |
|---|---|---|
| Specimen size | 100 ± 1 mm × 200 ± 1 mm | Cut with a sharp template or rotary cutter |
| Number of specimens per direction | Minimum 5 | More specimens may be needed for high variability |
| Gage length (jaw separation) | 75 ± 1 mm | Set before each test sequence |
| Rate of extension (CRE) | 300 ± 10 mm/min | For constant-rate-of-extension machines |
| Jaw face width | At least 25 mm | Typically 25 mm × 25 mm |
| Conditioning environment | 20 ± 2 °C, 65 ± 5 % RH | 24 h minimum; for wet testing, immerse 1 h |
Implementation Highlights and Best Practices
Grip Selection and Maintenance
To avoid jaw breaks (breakage directly at or near the grip edge), ensure the jaw faces are clean and free from fabric residues. Serrated jaw faces may reduce slippage but can introduce stress concentrations. Smooth faces with rubber facings are recommended for delicate fabrics. Regularly check the grip alignment so that the specimen is pulled symmetrically.
Good Practice: Include a standard reference fabric in each test run to monitor machine performance and operator consistency. This helps identify drift in test results before it becomes a compliance issue.
Handling of Specimens
Always handle conditioned specimens with clean gloves to avoid contamination (oils, moisture) that can alter strength. When cutting specimens, ensure the fabric is flat and free of wrinkles. Discard any specimen that is flawed, contains creases, or shows damage.
Reporting Results
Results should include: average breaking strength for each direction, the number of specimens tested, standard deviation, coefficient of variation, and details of any abnormal breaks (e.g., jaw breaks, slippage). If wet testing was performed, indicate the soaking time and temperature.
Compliance Notes and Quality Assurance
Laboratories seeking accreditation to CAN CGSB 4.2 No. 9.2-M90 (2013) must demonstrate compliance with the standard through regular proficiency testing and equipment calibration. The standard is recognized by the Standards Council of Canada (SCC) as part of the National Standards System.
Equipment Calibration
The tensile testing machine should be verified for force accuracy (e.g., annually) using traceable weights or load cells. The rate of extension should be checked periodically with a stopwatch and displacement gauge. Jaw separation should be set with a precision ruler or gauge block.
Non-Compliance Risk: Using an uncalibrated machine or failing to condition specimens can produce results that deviate from the true value by more than 10 %, making them unsuitable for acceptance testing. Such results could lead to incorrect product approval or rejection.
Interlaboratory Comparisons
Participation in interlaboratory studies (e.g., organized by ASTM or AATCC) helps validate that a laboratory’s results are consistent with others using the same method. The precision statement in the standard (from earlier CGSB studies) can be used as a benchmark: for most woven fabrics, the within-laboratory coefficient of variation is typically 4–6 %, and between-laboratory CV is 8–12 %.
Updates and Reaffirmation
CAN CGSB 4.2 No. 9.2-M90 was reaffirmed in 2013, meaning the technical content was reviewed and deemed still current. Users should verify if any amendments or newer editions have been published. The standard can be purchased from the CGSB online store or accessed through subscription services.
Frequently Asked Questions
Q: What is the difference between the grab method and the strip method?
A: In the grab method, only the central 25 mm width of a 100 mm wide specimen is clamped, leaving the outer edges unconstrained. The strip method uses a specimen of 50 mm or 25 mm full width clamped across the entire width. The grab method better simulates fabric behavior in end-use where the fabric is not rigidly restrained at the edges. It typically gives higher breaking strength values than the strip method for the same fabric.
A: In the grab method, only the central 25 mm width of a 100 mm wide specimen is clamped, leaving the outer edges unconstrained. The strip method uses a specimen of 50 mm or 25 mm full width clamped across the entire width. The grab method better simulates fabric behavior in end-use where the fabric is not rigidly restrained at the edges. It typically gives higher breaking strength values than the strip method for the same fabric.
Q: Can this standard be used for nonwoven fabrics?
A: Yes, the grab method is applicable to most nonwoven fabrics, provided they have sufficient integrity to be gripped without slippage. For very lightweight or stretchy nonwovens, the modified grab test (ASTM D5034) may be considered, but CGSB does not currently have a separate modified method. Users should carefully evaluate the specimen behavior.
A: Yes, the grab method is applicable to most nonwoven fabrics, provided they have sufficient integrity to be gripped without slippage. For very lightweight or stretchy nonwovens, the modified grab test (ASTM D5034) may be considered, but CGSB does not currently have a separate modified method. Users should carefully evaluate the specimen behavior.
Q: Is the 2013 reaffirmation still current, or is there a newer edition?
A: As of 2025, no newer edition has been published. The reaffirmation in 2013 confirmed that the standard is still technically relevant. However, users are encouraged to check with CGSB regularly for any updates or amendments.
A: As of 2025, no newer edition has been published. The reaffirmation in 2013 confirmed that the standard is still technically relevant. However, users are encouraged to check with CGSB regularly for any updates or amendments.
Q: How do I report results if some specimens break at the jaws?
A: Jaw breaks should be noted in the test report. If more than 25 % of specimens in a set are jaw breaks, the test may be considered invalid, and the cause (e.g., worn grips, high grip pressure) should be investigated. Results from jaw breaks are still included in the average unless otherwise specified, but they can bias the data low.
A: Jaw breaks should be noted in the test report. If more than 25 % of specimens in a set are jaw breaks, the test may be considered invalid, and the cause (e.g., worn grips, high grip pressure) should be investigated. Results from jaw breaks are still included in the average unless otherwise specified, but they can bias the data low.