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D5323-19 – Standard Test Method Technical Guide
📐 Scope and Applicability
This practice (D5323 −19a) standardizes the determination of the 2 % secant modulus for polyethylene geomembranes. It applies to materials 0.5 mm to 5 mm thick, specifically using tensile data from D6693/D6693M.
The goal is to standardize the derivation of points on the stress-strain curve, facilitating reliable modulus comparisons between materials.
Note: Standard values are in SI units (MPa). Values in parentheses (psi) are for information only.
⚙️ Significance and Terminology
Determining the elastic modulus tangent for polyethylene is difficult due to its non-linear stress-strain behavior. This leads to wide result variation. The 2 % secant modulus provides a reproducible alternative for quality control and material comparisons.
Key Definitions:
- Modulus of Elasticity: Ratio of stress to strain below the proportional limit (often impractical for polyethylene).
- Secant Modulus: Ratio of stress to strain at a specified point on the curve (here, 2% strain).
Important Distinction: Secant modulus approximates elastic modulus but generally yields a lower value, offering superior reproducibility for comparisons.
| 🟦 Term | 📏 Definition | ⚡ Units |
|---|---|---|
| Modulus of Elasticity | Stress/strain below proportional limit | MPa (FL⁻²) |
| 2% Secant Modulus | Stress/strain at 2% strain on curve | MPa (FL⁻²) |
| Stress (Nominal) | Force per original cross-sectional area | MPa (psi) |
📊 Procedure and Data Calculation
The calculation involves plotting the stress-strain curve from D6693/D6693M. A line from the origin to the point at 2% strain is drawn. The slope of this line is the 2 % secant modulus.
| 🟦 Parameter | 📐 Specification |
|---|---|
| Thickness Range | 0.5 mm to 5 mm (20 mil to 200 mil) |
| Reference Standard | D6693/D6693M |
Target Strain
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