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CAN CGSB 4.175-M91 Part 4 (2013): Standard Test Method for Breaking Strength of Textile Fabrics (Grab Method)
Scope, Technical Requirements, and Compliance Notes for the Canadian Standard on Grab Tensile Testing of Woven and Nonwoven Textiles
Introduction
CAN CGSB 4.175-M91 Part 4 (2013) is a test method standard published by the Canadian General Standards Board (CGSB) for determining the breaking strength of textile fabrics using the grab method. This standard is part of the CGSB 4.175 Textile Test Methods series and was originally developed in 1991 (M91) with reaffirmation in 2013 to ensure continued relevance. It is widely referenced in Canadian textile quality control, procurement specifications, and regulatory compliance frameworks. The grab method measures the tensile force required to rupture a fabric specimen held at the center by two pairs of jaws, simulating the distribution of stresses experienced by fabrics in many end-use applications.
Scope of the Standard
CAN CGSB 4.175 Part 4 applies to the determination of breaking strength and elongation of textile fabrics, including woven and nonwoven materials, provided they are of sufficient width to accommodate the grab test specimen. The method is particularly suited for fabrics where the strip method (covered in Part 3) may not adequately represent the in-service stress behavior. Products typically tested include apparel fabrics, industrial textiles, geotextiles, and upholstery materials.
The standard explicitly excludes fabrics that exhibit high stretch (e.g., elastic or elastomeric fabrics) unless specifically agreed upon by contract parties. It also does not cover narrow-width fabrics (less than 150 mm) for which specialized methods exist. The test is performed on conditioned specimens, complying with the textile conditioning standard referenced in CAN CGSB 4.2 (Standard Textile Conditioning).
Important: Fabrics that yield a breaking load outside the calibrated range of the tensile testing machine or require a jaw separation exceeding the maximum travel of the apparatus may not be tested in accordance with this standard without modification.
Technical Requirements and Test Procedure
Test Apparatus
The method requires a constant-rate-of-extension (CRE) tensile testing machine equipped with grab jaws. The lower jaw is stationary, while the upper jaw moves at a controlled speed. Key specifications include:
| Parameter | Requirement |
|---|---|
| Specimen width | 100 ± 1 mm (grab test) – jaws hold a 25 × 25 mm area at center |
| Gage length (distance between jaws) | 75 ± 1 mm |
| Rate of extension | 300 ± 10 mm/min |
| Number of specimens (per direction) | At least 5 in each of warp (length) and weft (width) directions |
| Conditioning atmosphere | 20 ± 2°C, 65 ± 4% RH for at least 24 hours |
| Pre-tension | Minimal, only sufficient to remove slack |
Specimen Preparation
Specimens are cut to a width of 100 ± 1 mm and a length of at least 200 mm. They must be conditioned in the standard atmosphere for at least 24 hours. Each specimen is taken from a representative sample, avoiding areas within 150 mm of the fabric edge. For direction testing, separate sets of specimens are cut parallel to the warp and weft directions. The number of specimens per direction is specified as a minimum of five, but for higher precision, additional replicates may be required.
Test Procedure
The test specimen is mounted centrally in the grab jaws such that the long dimension is parallel to the direction of extension. The jaws of the tensile machine are brought to the nominal gage length, and the load is applied at the standard rate until the specimen breaks. The maximum force recorded is the breaking strength (in Newtons). The elongation at break (in millimeters or percent) may be recorded if required.
If a specimen breaks at the edge of the jaw, the result may be discarded and a new test performed, as such failures often indicate jaw damage or stress concentration. The average and standard deviation are calculated for each direction.
Proper calibration of the tensile testing machine, including verification of load cell accuracy and speed of extension, is essential for valid results. Annual calibration against traceable standards is recommended.
Implementation and Compliance Notes
Use in Quality Assurance
CAN CGSB 4.175 Part 4 is frequently referenced in procurement contracts for textile products sold in Canada. Manufacturers and suppliers can use the method to demonstrate compliance with minimum breaking strength requirements. The test results serve as a basis for fabric performance evaluation, defect analysis, and product litigation.
Reporting Requirements
A test report must include the following elements: identification of the fabric sample, conditioning details, number of specimens per direction, individual breaking strength values, arithmetic mean and standard deviation for each direction, any observed failure mode, and details of any deviations from the standard procedure.
For comparative purposes, the grab method yields higher breaking strength values than the strip method for the same fabric, because a larger portion of the fabric width contributes to load bearing. Ensure that your specification clearly references CAN CGSB 4.175 Part 4.
Compliance Considerations
When using this standard in a regulatory or contractual context, it is important to:
- Ensure all testing personnel are familiar with the specific requirements of the 2013 reaffirmation.
- Use a conditioning system that meets the standard temperature and humidity tolerances.
- Maintain records of machine calibration and verification.
- Where a product standard references a specific part of CGSB 4.175, ensure Part 4 is the correct method for the property being assessed.
Misinterpretation of the grab method as applicable to narrow-width fabrics or highly stretchable materials can lead to invalid results and non-compliance. Always confirm the fabric type and specification before selecting the test method.
Frequently Asked Questions
Q: What is the main difference between the grab method (Part 4) and the strip method (Part 3)?
A: In the grab method, the jaws clamp only the central portion of the specimen (25 mm width), allowing the full fabric width (100 mm) to contribute to the load distribution. The strip method uses jaws that clamp the entire specimen width (typically 50 mm). The grab method is more representative of typical in-use fabric stresses and generally yields higher breaking loads.
A: In the grab method, the jaws clamp only the central portion of the specimen (25 mm width), allowing the full fabric width (100 mm) to contribute to the load distribution. The strip method uses jaws that clamp the entire specimen width (typically 50 mm). The grab method is more representative of typical in-use fabric stresses and generally yields higher breaking loads.
Q: Can CAN CGSB 4.175 Part 4 be used for nonwoven textiles?
A: Yes, the standard applies to nonwoven fabrics provided the specimen width requirements are met. However, for some nonwovens that do not exhibit a pronounced break, the strain at maximum force may need to be recorded as the breaking elongation.
A: Yes, the standard applies to nonwoven fabrics provided the specimen width requirements are met. However, for some nonwovens that do not exhibit a pronounced break, the strain at maximum force may need to be recorded as the breaking elongation.
Q: What should be done if a specimen breaks at the jaw edge?
A: Jaws edge breaks are considered indicative of stress concentration and may be discarded. Retest using a new specimen. If consistent jaw-edge breaks occur, check the jaw alignment, condition, or consider using a different method (e.g., strip method) as agreed upon by involved parties.
A: Jaws edge breaks are considered indicative of stress concentration and may be discarded. Retest using a new specimen. If consistent jaw-edge breaks occur, check the jaw alignment, condition, or consider using a different method (e.g., strip method) as agreed upon by involved parties.