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CAN CGSB 4.2 No. 26.2-94 (2012): Breaking Strength of Textile Fabrics — Grab Method Test Standard
A comprehensive technical review of the standard method for evaluating the tensile breaking strength and elongation of textile fabrics using the Grab test with Constant-Rate-of-Extension (CRE) tensile testing machines.
Scope and Purpose of CAN CGSB 4.2 No. 26.2-94 (2012)
CAN CGSB 4.2 No. 26.2-94 (2012) is a National Standard of Canada published by the Canadian General Standards Board (CGSB). It specifies a standard test method for determining the tensile breaking strength and elongation of textile fabrics using the Grab test procedure on a Constant-Rate-of-Extension (CRE) tensile testing machine. This method is applicable to a wide range of woven, nonwoven, and felted fabrics, as well as certain knitted fabrics where the fabric is stable enough to be successfully gripped by the specified clamp sizes.
The primary purpose of this standard is to provide a uniform, reproducible testing procedure inherent to the Grab method. Unlike the Strip method (CAN CGSB 4.2 No. 26.1), which tests a narrow raveled strip of fabric, the Grab method clamps only the center portion of a wider specimen. This approach more closely simulates the stress conditions a fabric experiences in actual use, where forces are not distributed perfectly across the entire fabric width but are localized around seams, buttons, or fasteners. The 2012 reaffirmation ensures the standard remains aligned with modern laboratory practices, specifically mandating the use of CRE machines over the historically prevalent Constant-Rate-of-Traverse (CRT) pendulum testers.
Important Note on Alignment: While CAN CGSB 4.2 No. 26.2-94 (2012) shares fundamental principles with ASTM D5034 and ISO 13934-2, specific conditioning environments, specimen dimensions, and reporting criteria may differ. Laboratories operating under Canadian regulatory frameworks or supply chain agreements must adhere strictly to the CGSB text to ensure compliance.
Technical Requirements and Test Procedure
Apparatus and Standard Test Parameters
The standard mandates precise specifications for the test apparatus and the preparation of specimens. The key technical parameters that must be strictly observed are summarized in the following table:
| Parameter | Specification (CAN CGSB 4.2 No. 26.2-94) |
|---|---|
| Machine Type | Constant-Rate-of-Extension (CRE) with autographic recorder |
| Jaw Faces | 25 mm x 25 mm (±1 mm) standard; 25 mm x 50 mm alternative permitted |
| Gauge Length | 75 mm ± 1 mm (3 in ± 0.04 in) |
| Rate of Extension | 300 mm/min ± 10 mm/min (12 in/min ± 0.4 in/min) |
| Specimen Size | 100 mm ± 1 mm x 150 mm ± 1 mm (4 in x 6 in) |
| Minimum Number of Specimens | 5 warp (or lengthwise) and 5 weft (or crosswise) |
| Standard Conditioning Atmosphere | 65% ± 2% RH, 21°C ± 1°C for a minimum of 24 hours |
Specimen Preparation and Mounting
For woven fabrics, specimens are cut 100 mm wide by 150 mm long. The longer dimension of the specimen must be parallel to the direction being tested (warp or weft). It is critical that the 25 mm jaws clamp the fabric centrally, with the 75 mm gauge length established accurately. The outer longitudinal edges of the specimen remain entirely free, which defines the “Grab” geometry. The standard explicitly requires that the specimen be large enough that the jaws are at least 20 mm away from the outer edges of the specimen.
Any specimen that breaks in, or within 5 mm of, the jaw faces must have its result discarded. An additional test specimen from the same sample must be tested to replace the discarded result. This ensures that the recorded breaking load is representative of the fabric’s inherent tensile properties and not an edge-effect or jaw-induced failure.
Implementation Tip: Proper pretensioning is critical for accurate elongation data. The standard recommends a pretension of 0.1 ± 0.02% of the expected breaking load. For delicate or highly extensible fabrics, ensure the clamping pressure prevents slippage without causing jaw breaks. Pneumatic clamps set to a consistent pressure are highly recommended for reproducible results across a testing batch.
Implementation Highlights and Industry Use
The Grab method holds significant importance in quality control and materials acceptance testing. It is particularly prevalent in the evaluation of high-performance technical textiles, including those used in industrial fabrics and protective clothing. The method is frequently cited in related Canadian government procurement specifications for textiles (e.g., uniforms and tents), where the fabric must withstand localized stresses that the Grab method effectively simulates.
When implementing this standard, it is vital to understand its relationship to the companion standard, CAN CGSB 4.2 No. 26.1 (Strip Method). The key differences are:
- Specimen Width: The Strip method requires a raveled strip of a specific width (e.g., 50 mm), while the Grab method uses a wider (100 mm) specimen clamped only in the center.
- Result Interpretation: Grab test results are typically higher than Strip test results for the same fabric. This is because the unclamped edges of the Grab specimen provide lateral support to the yarns in the clamped area, simulating the mutual support found in an actual sewn seam.
- Application: The Grab method is the preferred method for fabrics that are difficult to ravel, industrial textiles, and heavy-weight fabrics, while the Strip method is often specified for tightly woven apparel textiles.
Precision and Bias: Interlaboratory comparison data for this standard indicates that for most homogeneous woven fabrics, the variability between laboratories is typically below 10% when using CRE machines. The precision is significantly better than the older CRT methods, justifying the mandatory transition in the 2012 reaffirmation. Proper specimen conditioning is the single largest contributor to minimizing within-laboratory variability.
Compliance and Reporting Notes
Full compliance with CAN CGSB 4.2 No. 26.2-94 (2012) requires rigorous adherence to the prescribed sampling plan, conditioning protocol, and testing machine verification. The standard specifies that the test report must include the following items to be considered compliant:
- Number of specimens tested and the number of specimens discarded (e.g., due to jaw breaks).
- The average breaking force reported in Newtons (N) or kilogram-force (kgf).
- The average elongation at break expressed as a percentage of the gauge length (75 mm).
- A statement confirming whether the standard conditioning atmosphere was used or if an alternative was employed.
- A clear reference to the standard: CAN CGSB 4.2 No. 26.2-94 (2012), including any agreed-upon deviations from the standard procedure.
Critical Machine Requirement: CAN CGSB 4.2 No. 26.2-94 (2012) strictly requires a Constant-Rate-of-Extension (CRE) machine. Laboratory test systems based on a Constant-Rate-of-Traverse (CRT) principle, such as traditional pendulum-type testers, are not compliant with this version of the standard. Testing programs must ensure their equipment is capable of maintaining the specified rate of extension within the ±10 mm/min tolerance across the entire breaking range of the fabric.
Frequently Asked Questions (FAQs)
Q: What is the main difference between CAN CGSB 4.2 No. 26.2 (Grab method) and No. 26.1 (Strip method)?
A: The primary difference is specimen preparation and clamping geometry. The Strip method uses a narrow, raveled strip clamped across its entire width. The Grab method uses a wider specimen but clamps only the central 25 mm portion. The Grab method measures the fabric’s resistance to localized tensile stress, while the Strip method measures the absolute breaking force of a defined set of yarns.
A: The primary difference is specimen preparation and clamping geometry. The Strip method uses a narrow, raveled strip clamped across its entire width. The Grab method uses a wider specimen but clamps only the central 25 mm portion. The Grab method measures the fabric’s resistance to localized tensile stress, while the Strip method measures the absolute breaking force of a defined set of yarns.
Q: Why was the 2012 reaffirmation significant for this standard?
A: The 2012 reaffirmation was crucial because it formally removed the option to use Constant-Rate-of-Traverse (CRT) testing machines. This aligned the CGSB method with the global textile testing standard (ISO 13934-2 and ASTM D5034), which had fully transitioned to Constant-Rate-of-Extension (CRE) technology for its superior accuracy in force measurement and rate control.
A: The 2012 reaffirmation was crucial because it formally removed the option to use Constant-Rate-of-Traverse (CRT) testing machines. This aligned the CGSB method with the global textile testing standard (ISO 13934-2 and ASTM D5034), which had fully transitioned to Constant-Rate-of-Extension (CRE) technology for its superior accuracy in force measurement and rate control.
Q: Can this method be applied to knitted fabrics?
A: Yes, the scope includes knitted and nonwoven fabrics, provided they can be successfully clamped without damage or excessive slippage. However, the standard notes that knitted fabrics often exhibit very high elongation, which requires careful monitoring to ensure the machine can maintain the specified rate of extension through the entire break cycle without reaching its travel limits.
A: Yes, the scope includes knitted and nonwoven fabrics, provided they can be successfully clamped without damage or excessive slippage. However, the standard notes that knitted fabrics often exhibit very high elongation, which requires careful monitoring to ensure the machine can maintain the specified rate of extension through the entire break cycle without reaching its travel limits.
Q: What are typical causes of high variability in Grab test results?
A: The most common causes are inadequate specimen conditioning (leading to fluctuating moisture content), improper gripping pressure (causing jaw breaks or slippage), and failure to accurately align the specimen so the line of action is perpendicular to the jaws. Strict adherence to the 75 mm gauge length is also critical.
A: The most common causes are inadequate specimen conditioning (leading to fluctuating moisture content), improper gripping pressure (causing jaw breaks or slippage), and failure to accurately align the specimen so the line of action is perpendicular to the jaws. Strict adherence to the 75 mm gauge length is also critical.
This technical article is based on the CAN CGSB 4.2 No. 26.2-94 (2012) standard. For specific testing protocols and regulatory requirements, always refer directly to the official published document from the Canadian General Standards Board. Last reviewed: 2026.