ASTM Standards to determine the strength and elasticity of spandex fabrics
When determining the strength of spandex fabrics, the focus isn't just on ultimate breaking strength like traditional textiles, but critically on their elastic properties, how much they stretch under tension and how well they recover. Here are the ASTM standards used for evaluating the strength and elastic properties of spandex fabrics:
- ASTM D4964: Standard test method for tension and elongation of elastic fabrics (constant-rate-of-extension type tensile testing machine)
- Scope: This is the primary and most relevant standard for spandex fabrics. It specifically covers the measurement of tension (force) and elongation (stretch) of wide or narrow elastic fabrics made from natural or man-made elastomers (like spandex), alone or in combination with other textile yarns.
- What it measures:
- Tension at specified elongation: The force required to stretch the fabric to a certain percentage of its original length. This is crucial for understanding how much "power" the fabric has.
- Elongation at specified tension: The amount the fabric stretches when a specific force is applied.
- Tension-recovery curves: These curves show the fabric's behavior during loading and unloading cycles, providing insights into its elastic recovery.
- Methodology: It uses a Constant-Rate-of-Extension (CRE) type tensile testing machine. Specimens are typically cycled multiple times and data from the third cycle is often used for analysis to account for initial stretch/relaxation.
- Importance: This standard is vital for assessing the performance, quality, and durability of elastic fabrics in applications where fit, comfort, and shape retention are critical (eg: swimwear, activewear, foundation garments).
- ASTM D2594: Standard test method for stretch properties of knitted fabrics having low power
- Scope: While not exclusively for spandex, this standard is applicable to knitted fabrics that exhibit high stretch and good recovery from low tension. Many spandex-blended knits would fall under this category.
- What it measures:
- Fabric stretch: The elongation of the fabric when a known load is applied.
- Fabric growth: The extension remaining in the fabric after a known extension has been applied and subsequently removed (i.e., how much it "grows" or stretches permanently after being extended).
- Relationship to D4964: D2594 is specifically for "low power" knitted fabrics, and it notes that fabrics intended for support or other applications requiring "high-power" stretch are better evaluated using methods like D4964.
- ASTM D6614: standard test method for stretch properties of textile fabrics ‘CRE method’
- Scope: This standard covers the determination of fabric stretch and fabric growth after a specified extension and held for a specified time. It's a general method for textile fabrics but is often used for fabrics with stretch properties.
- Relationship to other standards: Like D2594, it also mentions that knit fabrics having high stretch are better measured by D2594, and it explicitly states it should not be used for breaking strength and elongation of woven fabrics (which are covered by D5034 and D5035).
Other relevant ASTM standards (for general textile strength, which can be applied to spandex blends but not solely spandex):
- ASTM D5034: Standard test method for breaking strength and elongation of textile fabrics (grab test)
- ASTM D5035: Standard test method for breaking force and elongation of textile fabrics (strip test)
These two are general tensile strength tests for textile fabrics. While they measure the ultimate breaking strength and elongation, they are less specific to the elastic performance (stretch and recovery) that is paramount for spandex. They would be used for fabrics where spandex is a component, and overall fabric integrity under breaking force is important. When dealing with spandex, ASTM D4964 is one of the most direct and comprehensive standard for evaluating its characteristic elastic strength and recovery properties. Always ensure you refer to the latest versions of these ASTM standards, as they are periodically updated.