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D434-95 – Standard Test Method Technical Guide
⚙️ Test Method Overview and Significance
This standard test method, designated ASTM D 434-95, covers the determination of the resistance to slippage of filling yarns over warp yarns, or warp yarns over filling yarns, using a standard seam. It is widely used in the trade for acceptance testing and provides a critical indication of a fabric’s tendency to fail at a seam due to yarn migration, which is generally not repairable.
Resistance to yarn slippage is defined as the force required to separate the parts of a standard seam assembly by a specified amount. The method operates by comparing the superimposed load-elongation curves of the fabric, with and without a standard seam sewn parallel to the yarns being tested. The separation of these curves at a predetermined distance indicates the point of yarn slippage.
⚠️ Important Limitation: This test method is explicitly not intended for upholstery fabrics.
📐 Apparatus and Test Parameters
The test requires a Constant-Rate-of-Traverse (CRT) tensile testing machine of the pendulum type, equipped with an autographic recorder and conforming to the requirements of Specification D 76. Clamps must have front jaws 1 in. (25 mm) in width and back jaws 2 in. (50 mm) or more in width. The standard gage length between clamps is set to 3 in. (75 mm), and the speed of the lower clamp is specified at 12 ± 0.5 in./min (300 ± 10 mm/min).
The standard seam is sewn parallel to the yarns being tested per Federal Standard No. 751a. Specimens must be conditioned according to Practice D 1776 prior to testing.
| 🟦 Parameter | 📏 Specification |
|---|---|
| Clamp Jaw Width (Front) | 1 in. (25 mm) |
| Clamp Jaw Width (Back) | ≥ 2 in. (50 mm) |
| Gage Length | 3 in. (75 mm) |
| Speed of Lower Clamp | 12 ± 0.5 in./min (300 ± 10 mm/min) |
| Standard Specified Separation | ¼ in. (6.4 mm) |
| Seam Elongation Compensation | 1 lbf (4.45 N) |
📊 Interpreting Test Results
Resistance to yarn slippage is reported as the force at which the load-elongation curve of the fabric with the seam is a predetermined distance greater than the load-elongation curve of the fabric without the seam. The result is reported in units of pounds-force per inch (newtons per metre). A standard compensation of 1 lbf (4.45 N) is deducted from the total load to account for the inherent elongation of the seam structure, yielding the net slippage resistance. While a ¼-in. (6.4-mm) separation is standard, a smaller opening may be preferred for some fabrics.
💡 Interlaboratory Comparison: In cases of disagreement between purchaser and seller, the statistical bias between laboratories should be determined by testing specimens randomly drawn from a single sample. This method can also be used to evaluate the correlation between CRE and CRI testing machines.
❓ Frequently Asked Questions
🔍 What is the standard gage length for the ASTM D 434-95 test?
The tensile testing machine clamps are set to a gage length of precisely 3 in. (75 mm).
💡 How is the seam compensation applied to the test results?
A compensation of exactly 1 lbf (4.45 N) is deducted from the recorded force to allow for the elongation of the seam itself, ensuring the final value purely represents the resistance to yarn slippage.
⚡ What separation distance is typically used to define failure?
The standard specified separation between the parts of the seam assembly is ¼ in. (6.4 mm). For some specific fabric types, a smaller opening may be used as an alternative.
📌 What are the key reference documents for this standard?
Primary references include Specification D 76 for tensile testing machines, Terminology D 123, Test Methods D 1682, Practice D 1776 for conditioning, and Federal Standard 751a for the standard seam stitching.