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D2594 – Standard Test Method Technical Guide
ASTM D2594/D2594M-21 defines a standard test method specifically designed for evaluating the stretch and growth characteristics of knitted fabrics that exhibit high extension under low tension, commonly referred to as low-power stretch fabrics. Unlike tests for rigid or power-net fabrics, this method employs a unique looped specimen geometry to accurately measure fabric behavior without interference from clamping stresses.
This standard is under the jurisdiction of ASTM Committee D13 on Textiles and provides two distinct procedures that can be used together or independently. The values stated in either SI units or inch-pound units shall be regarded separately, ensuring strict compliance by using each system without combination. For fabrics intended for support or other high-power applications, the standard recommends referring to Test Methods D3107, D4964, or D6614.
📐 Specimen Geometry and Types
The test method requires a rectangular fabric specimen whose cut ends are joined to form a continuous loop. This looped configuration is a hallmark of D2594, specifically designed to avoid the grip-related stress concentrations and slippage that can compromise the measurement of highly extensible knits. Bench marks are applied to the fabric surface to define the initial gauge length for extension measurement, with terminology sourced from D4849. Conditioning of all test specimens must be carried out in accordance with Practice D1776 to standardize moisture and temperature effects.
📌 Technical Note: The looped specimen design is critical for low-power knits. By avoiding direct clamping of the fabric ends, the test measures true fabric stretch behavior rather than jaw-induced artifacts, providing a more accurate representation of fabric performance during garment construction and wear.
⚙️ Test Procedure for Stretch and Growth
Fabric Growth
The fabric growth procedure evaluates the permanent deformation or “sag” of the fabric. A specified tension is applied to the looped specimen until it reaches a predetermined elongation. The specimen is then held at this elongation for 2 hours. Immediately after the tension is removed, the percent change in specimen length is recorded as the immediate growth. The specimen is then allowed to recover for 1 hour without tension, after which the residual growth is measured. This sequence simulates the fabric’s recovery after a prolonged period of wear extension.
Fabric Stretch
A specified tension is applied to and completely removed from the looped fabric specimen for five complete cycles to mechanically condition the fabric. On the fifth application of tension, the load is held and the percent change in the length between the bench marks is measured. This value represents the conditioned fabric stretch, reflecting the stabilized extensibility of the fabric under a specific low tensile load.
| 🟦 Parameter | 📏 Fabric Growth | 🎯 Fabric Stretch |
|---|---|---|
| Specimen Configuration | Looped (cut ends joined) | Looped (cut ends joined) |
| Applied Condition | Held at specified elongation | Cycled at specified tension |
| Cycle / Hold Time | Held for 2 hours | 5 loading/unloading cycles |
| Measurement Timing | Immediate & after 1 h recovery | On the 5th cycle under load |
| Key Calculation | % Elongation remaining after release | % Extension under load |
📊 Key Measured Properties
The standard quantifies two primary properties that define the elastic performance of low-power knit fabrics:
- Fabric Stretch: The conditioned extension of the fabric under a specified low tensile load. This property indicates how much a fabric can stretch during wear, such as over a knee or elbow, under light tension.
- Fabric Growth: The residual extension of the fabric after it has been subjected to a sustained elongation and then allowed to recover. The immediate growth and the growth after 1 hour of recovery provide a measure of the fabric’s elastic hysteresis and its ability to return to its original shape.
Definitions for these terms are standardized in Terminology D4850, while related terms like “bench marks” are sourced from Terminology D4849.
💡 Technical Tip: The specific elongation for the growth test and the specific tension for the stretch test are typically specified in the material specification or agreed upon between the purchaser and the supplier. These values should be chosen to reflect the intended end-use of the fabric to ensure relevant performance data.
❓ Frequently Asked Questions
🔍 What distinguishes D2594 from other stretch fabric tests like D4964?
D2594 is specifically designed for low-power knitted fabrics using a unique looped specimen to avoid jaw effects. D4964 is designed for higher-power elastic fabrics and uses a constant-rate-of-extension (CRE) tensile testing machine with standard clamps. D6614 provides a CRE method for general textile fabrics. The