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CAN CGSB 4.2 No. 2-M88 (2013): Breaking Strength of Fabrics – Strip Method – A Comprehensive Technical Guide
An In-Depth Examination of the Canadian Standard for Textile Tensile Testing Using the Strip Method
The standard CAN CGSB 4.2 No. 2-M88 (2013) is a cornerstone of textile testing in Canada. It specifies the strip method for determining the breaking strength and elongation of textile fabrics. This method involves testing a strip of fabric of a specified width, gripped across its entire width in the jaws of a tensile testing machine, and pulling until rupture. The standard is part of the CGSB 4.2 series of textile test methods and was reaffirmed in 2013 to remain current. This article provides a detailed overview of its requirements, implementation, and significance for quality assurance.
1. Scope
CAN CGSB 4.2 No. 2-M88 (2013) applies primarily to woven fabrics but is also suitable for nonwoven fabrics and certain knitted fabrics where the strip method is considered appropriate. The standard covers the determination of maximum force (breaking strength) and elongation at maximum force using a constant-rate-of-extension (CRE) tensile testing machine. It is applicable to specimens that are either conditioned or wet, as per specific testing requirements.
The strip method (as opposed to the grab method) utilizes the full width of the specimen within the clamps, providing a measure of fabric strength that is influenced by both yarn strength and fabric construction. The standard is widely referenced in procurement specifications and quality control programs for textile products in Canada.
Tip: For fabrics with high elongation (>8%), use the 300 mm/min rate to complete the test within a reasonable time and to avoid excessive damage to the specimen.
2. Technical Requirements
2.1 Principle
A rectangular strip of fabric of specified width is mounted centrally in the jaws of a tensile testing machine. A force is applied at a constant rate of extension until the specimen ruptures. The maximum force recorded is the breaking strength, and the corresponding elongation is the elongation at break.
2.2 Apparatus
- CRE Tensile Testing Machine – capable of recording force and elongation. The machine must be capable of maintaining the specified rate of extension.
- Jaws – The jaw faces must be at least as wide as the specimen width and should provide uniform clamping without slippage. The gauge length (distance between jaws) is set as specified, typically 200 mm.
- Cutting Templates – Precise cutting equipment for preparing specimens of exact width.
- Conditioning Facility – Chamber or room maintaining the standard atmosphere for textile testing.
Caution: Sandpaper, rubber, or other gripping materials may be needed to prevent specimen slippage in the jaws. Ensure that jaw pressure is uniform to avoid edge damage.
2.3 Specimen Preparation
For woven fabrics, specimens are cut 30 mm to 35 mm wide and then raveled to a width of exactly 25 mm ± 1 mm by removing edge yarns. The length must be sufficient to allow a 200 mm gauge length plus extra for clamping (typically not less than 350 mm). Each specimen is taken with the longer dimension parallel to either the warp or weft direction, depending on the testing requirement.
For nonwoven fabrics, a 25 mm wide strip is cut directly. Specimens must be free from creases, folds, or any defects. A minimum of five specimens per direction (warp and weft) is required.
2.4 Conditioning
Specimens are conditioned in a standard atmosphere for textile testing: 20 ± 2°C and 65 ± 4% relative humidity for at least 24 hours, or until equilibrium is reached. For wet testing, specimens are immersed in distilled water containing a wetting agent for a specified duration.
Success: Proper specimen preparation – raveling to exactly 25 mm – reduces test variability and improves reproducibility between laboratories.
2.5 Procedure
Set the gauge length to 200 mm ± 1 mm. Choose the rate of extension:
- For fabrics with elongation at maximum force less than 8%, use (50 ± 10) mm/min.
- For fabrics with elongation 8% and above, use (300 ± 10) mm/min.
Mount each conditioned specimen centrally in the jaws with minimal slack. Start the machine and record the force-elongation curve. The machine continues until the specimen ruptures. Report the maximum force and the elongation at maximum force for each specimen.
2.6 Calculation and Expression of Results
Calculate the mean breaking strength and mean elongation for each set of specimens (warp and weft separately). Results are expressed in newtons (N) or kilograms-force (kgf) if required, and elongation as a percentage. Standard deviation and coefficient of variation may be calculated to assess variability.
The standard includes adjustments for specimens that break within 5 mm of the jaw edge (jaw breaks). Such results are discarded if the individual value is less than the force obtained in a test where the break occurs in the middle of the specimen.
| Fabric Type | Specimen Width (mm) | Gauge Length (mm) | Rate of Extension (mm/min) | Number of Specimens per Direction |
|---|---|---|---|---|
| Woven (warp/weft) | 25 ± 1 | 200 ± 1 | 50 or 300 | 5 |
| Nonwoven | 25 ± 1 | 200 ± 1 | 300 | 5 |
| Knitted (where applicable) | 25 ± 1 | 200 ± 1 | 300 | 5 |
Important: For wet testing, use the same parameters as for conditioned testing. Ensure that the specimens remain wet during the test by using a drip tray or periodic wetting.
3. Implementation Highlights
Implementing CAN CGSB 4.2 No. 2-M88 in a textile testing laboratory requires attention to several details:
- Alignment with ISO 13934-1: The Canadian strip method is harmonized with the international standard ISO 13934-1. Laboratories already following ISO 13934-1 will find the transition straightforward. However, slight differences in specimen conditioning and reporting may exist; it is important to indicate the specific standard used in test reports.
- Equipment Compliance: The tensile tester must be capable of providing the required rate of extension and accuracy. Load cell capacity should be selected based on the expected strength, typically 500 N to 5000 N.
- Recording and Software: Modern tensile testers automatically record and calculate results, but the algorithm should comply with the standard’s requirements for determining the maximum force from the curve.
- Quality Control: Include periodic verification of the machine with calibration weights and routine checks of specimen dimensions.
4. Compliance Notes
The standard is a voluntary consensus standard but is often mandatory when referenced in contracts, procurement documents, or regulations. Accreditation bodies (such as the Standards Council of Canada) may assess laboratories against this standard for testing. Compliance requires documented procedures, calibrated equipment, and trained personnel. The standard was reaffirmed in 2013, meaning that it was reviewed and confirmed as current without revision. Users should verify if any amendments have been issued since.
For international trade, many countries accept results based on harmonized standards such as ISO 13934-1. However, when testing for the Canadian market, CGSB standards are commonly specified.
Important: Non-compliance with conditioning requirements (temperature, humidity, duration) nullifies test validity. Always record the actual conditions in the test report.
Q: What is the difference between the strip method and the grab method in textile testing?
A: The strip method uses the full width of the specimen within the jaws (typically 25 mm), while the grab method uses only a portion of the specimen width and clamps near the center, leaving edges free. Strip method results are generally lower because the entire width is subjected to stress, making it more representative of the overall fabric strength.
A: The strip method uses the full width of the specimen within the jaws (typically 25 mm), while the grab method uses only a portion of the specimen width and clamps near the center, leaving edges free. Strip method results are generally lower because the entire width is subjected to stress, making it more representative of the overall fabric strength.
Q: Are there any special requirements for testing knitted fabrics according to this standard?
A: CAN CGSB 4.2 No. 2-M88 is primarily intended for woven fabrics. For knitted fabrics, the standard may be used with caution, but it is recommended to use test methods specific to knitted fabrics, such as CAN/CGSB 4.2 No. 9.2 or ISO 13934-1 with modifications. The strip method can be problematic for highly stretchable materials.
A: CAN CGSB 4.2 No. 2-M88 is primarily intended for woven fabrics. For knitted fabrics, the standard may be used with caution, but it is recommended to use test methods specific to knitted fabrics, such as CAN/CGSB 4.2 No. 9.2 or ISO 13934-1 with modifications. The strip method can be problematic for highly stretchable materials.
Q: How often should the tensile tester be calibrated?
A: The standard does not specify a frequency, but good laboratory practice dictates annual calibration by an accredited body, with daily verification using calibrated masses. This aligns with ISO 7500-1 requirements for force verification of tensile testing machines.
A: The standard does not specify a frequency, but good laboratory practice dictates annual calibration by an accredited body, with daily verification using calibrated masses. This aligns with ISO 7500-1 requirements for force verification of tensile testing machines.
Q: Can this standard be used for quality control of automotive textiles?
A: Yes, CAN CGSB 4.2 No. 2-M88 is often referenced in the automotive industry for testing interior textiles. However, specific automotive standards may have additional requirements. It is advisable to check the customer’s specification.
A: Yes, CAN CGSB 4.2 No. 2-M88 is often referenced in the automotive industry for testing interior textiles. However, specific automotive standards may have additional requirements. It is advisable to check the customer’s specification.
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