Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
CAN CGSB 4.2 No. 21-M90 (2013): Standard Test Method for Breaking Strength of Fabrics by the Grab Method
Essential Guidelines for Conducting Grab Tests on Woven and Nonwoven Fabrics Using CRE and CRT Machines
Scope and Application
CAN CGSB 4.2 No. 21-M90 (2013) specifies a grab method for determining the breaking strength of woven and nonwoven fabrics using either a constant-rate-of-extension (CRE) or constant-rate-of-traverse (CRT) testing machine. The test is widely used to evaluate the tensile properties of textile fabrics and is referenced in many Canadian product specifications. The standard applies to most woven and nonwoven fabrics but excludes those that are excessively stretchable or that require seam strength evaluation.
The grab method involves clamping a narrow central portion of the specimen, allowing the outer edges to be free. This configuration better simulates the way fabrics behave under localized stress, making it a preferred method for quality control and material acceptance.
The standard also includes guidance on conditioning of specimens, selection of test direction (warp and weft), and calculation of average breaking force.
Technical Requirements
Specimen Preparation: Specimens are cut to a width of 100 mm ± 2 mm and a length of at least 150 mm. The specimen is clamped in the grab jaws with a central jaw face width of 25 mm ± 1 mm and a clamping surface length of 75 mm. The outer fibers of the specimen remain unclamped.
Testing Speed: For CRE machines, the rate of extension is set at 300 mm/min ± 10 mm/min. For CRT machines, the rate of traverse is adjusted to achieve a mean time-to-break of 20 s ± 3 s. The standard provides a detailed procedure for adjusting the machine speed to achieve the desired breaking time.
Jaw Faces: Standard plain flat jaw faces are required, with the distance between jaws (gauge length) set at 75 mm ± 1 mm. The lower jaw is stationary while the upper jaw moves.
Number of Tests: At least five specimens per direction (warp and weft) must be tested. Results are reported as the mean breaking force in newtons, with calculations for standard deviation and coefficient of variation if required.
CRE machines provide a constant rate of extension throughout the test, which gives consistent results across a broad range of fabric types. CRT machines maintain a constant rate of jaw separation but the extension rate varies as the specimen elongates. The standard allows either type, but the machine used must be reported.
| Parameter | CRE (Constant-Rate-of-Extension) | CRT (Constant-Rate-of-Traverse) |
|---|---|---|
| Rate Control | Extension rate maintained constant | Traverse rate maintained constant, extension rate decreases |
| Typical Speed | 300 mm/min | Adjusted to 20 s mean break time |
| Preferred for | Most woven and nonwoven fabrics | Fabrics with low elongation or high modulus |
| Force Measurement | Load cell with ±1% accuracy | Pendulum or load cell with ±1% accuracy |
| Data Output | Digital force vs. extension curve | Analog or digital breaking force |
Implementation Highlights
Setting up a laboratory to perform grab testing per this standard requires:
- A universal testing machine (CRE or CRT) with grab jaws.
- Conditioning chamber or room to maintain standard atmosphere (20 °C ± 2 °C, 65 % ± 4 % relative humidity).
- Template for cutting specimens.
- Data recording software or load-display system.
Operators should be trained in fabric handling to avoid contamination or damage to specimens. It is important to ensure that the jaw face alignment is checked periodically using a calibrated steel strip. For CRT machines, the pendulum release mechanism should be tested for smooth operation.
The standard also suggests an optional seam slippage procedure, but this is provided in a separate method (CAN/CGSB-4.2 No. 21.5). When reporting breaking strength, always indicate if the fabric failed by yarn breakage, slippage, or a combination.
CRT machines can produce erroneous results if the pendulum friction is not properly maintained. Regular cleaning and verification of the pendulum angle are critical for accurate readings.
The grab method is particularly effective for fabrics where seam strength is a concern because it simulates the localized stress concentration found at seams. The standard provides a reliable basis for quality assurance in textile manufacturing.
Compliance Notes
Facilities performing tests according to CAN CGSB 4.2 No. 21-M90 must ensure their equipment meets the requirements for jaw dimensions, gauge length, and speed accuracy. Regular calibration of the force measurement system is mandatory. The standard references CAN/CGSB-4.2 No. 2 for conditioning atmospheres; specimens must be conditioned in a standard atmosphere of 20 °C ± 2 °C and 65 % ± 4 % relative humidity for at least 24 hours.
Key compliance points include:
- Verify that the grab jaws are aligned and free of wear.
- Confirm that the time-to-break for CRT machines is within 20 s ± 3 s for each specimen.
- Report machine type (CRE or CRT) in the test report.
- For arbitration, any test with a specimen breaking at the jaw edge should be discarded and retested.
The standard also offers guidance for automated testing systems, requiring that the machine meets the accuracy specifications of the manual procedure.
The test report must include: standard reference, specimen identification, direction (warp/weft), number of specimens, mean breaking force, standard deviation, type of machine used, and any departures from the standard.
A common mistake is using specimens with damaged edges or improper conditioning. Ensure that all specimens are cut using a sharp template and conditioned for at least 24 hours in the standard atmosphere before testing.
As of 2026, CAN CGSB 4.2 No. 21-M90 (2013) is reaffirmed and remains the primary method for grab testing in Canada.
Frequently Asked Questions
Q: What is the main difference between the grab method and the strip method for fabric breaking strength?
A: In the grab method, only the central portion of the specimen is clamped, leaving the edges free. This simulates the localized stress that occurs at seams. In the strip method, the full width of the specimen is clamped, which distributes stress across the entire fabric width. The grab method is considered more representative of actual end-use conditions for many apparel textiles.
A: In the grab method, only the central portion of the specimen is clamped, leaving the edges free. This simulates the localized stress that occurs at seams. In the strip method, the full width of the specimen is clamped, which distributes stress across the entire fabric width. The grab method is considered more representative of actual end-use conditions for many apparel textiles.
Q: Can I use a CRE machine if my laboratory only has a CRT machine?
A: Yes, the standard allows both CRE and CRT machines. However, you must ensure that the CRT machine is adjusted so that the mean time-to-break is 20 s ± 3 s. CRE machines are generally easier to operate and provide more consistent results, but both are acceptable if the specifications are met. It is important to identify the machine type in the test report.
A: Yes, the standard allows both CRE and CRT machines. However, you must ensure that the CRT machine is adjusted so that the mean time-to-break is 20 s ± 3 s. CRE machines are generally easier to operate and provide more consistent results, but both are acceptable if the specifications are met. It is important to identify the machine type in the test report.
Q: How many specimens are required for a valid test?
A: The standard requires at least five specimens per direction (warp and weft) for routine testing. If the coefficient of variation exceeds 5 %, additional specimens may be needed to achieve acceptable precision. For arbitration, it is recommended to test at least ten specimens per direction.
A: The standard requires at least five specimens per direction (warp and weft) for routine testing. If the coefficient of variation exceeds 5 %, additional specimens may be needed to achieve acceptable precision. For arbitration, it is recommended to test at least ten specimens per direction.
Q: What should I do if a specimen breaks at the jaw edge?
A: If any specimen breaks at or within 5 mm of the jaw line, the result should be discarded and a new specimen tested. This is to avoid artificially low breaking strength values caused by stress concentration near the clamps. In some cases, using jaw faces with a slightly more compliant surface may reduce jaw breaks.
A: If any specimen breaks at or within 5 mm of the jaw line, the result should be discarded and a new specimen tested. This is to avoid artificially low breaking strength values caused by stress concentration near the clamps. In some cases, using jaw faces with a slightly more compliant surface may reduce jaw breaks.