Information on the most widely used ASTM standards within the materials testing industry
ASTM D6693/D6693M Standard Test Method for Determining Tensile Properties of Nonreinforced Polyethylene and Nonreinforced Flexible Polypropylene Geomembranes
ASTM D6693 is the standard test method for determining the tensile properties of nonreinforced polyethylene and flexible nonreinforced polypropylene geomembranes using dumbbell-shaped specimens under defined pretreatment, temperature, and constant crosshead speed conditionsASTM International. It measures key mechanical properties including yield strength, break strength, yield elongation, break elongation, and modulus of elasticity.
Test Principle of ASTM D6693:
The principle is a standard tensile test applied to geomembranes. Through applies a uniaxial tensile load at a constant crosshead speed to standard dumbbell specimens, recording load vs. elongation to characterize the material’s response to tension.A dumbbell-shaped specimen is clamped in a tensile testing machine and stretched at a constant rate until it breaks. The force exerted and the elongation are measured continuously. From this data, key tensile properties are calculated, which are critical for quantifying the material's strength and ductility.
Identify the yield point (first significant deviation from linearity).
Measure ultimate tensile strength at break.
Calculate elongation as percentage change in gauge length.
Determine Young’s modulus from the initial linear region.
ASTM D6693 Geomembranes Test Specimen Information:
| Parameter | Specification |
|---|---|
| Material | Nonreinforced geomembranes based on polyethylene (PE) or flexible polypropylene (fPP). It is notintended for reinforced or rigid materials, or for materials like PVC or CSPE. |
| Shape | Dumbbell (Type IV per ASTM D638)
This shape is used to ensure failure occurs within the gage length and not at the grips. |
| Dimensions | - Overall length: ≥150 mm (6 in)- Gauge break length: 50 mm (2 in), Gauge yield length: 33mm - Gauge width: 6 mm (0.25 in)- Shoulder radius: 25 mm (1 in)
|
| Thickness Range | 0.25–6.3 mm (0.010–0.25 in) |
| Sampling Direction | 5 specimens in machine direction (MD), 5 in cross-machine direction (CD) |
| Direction | Specimens are cut and tested in both the machine direction (MD) and cross-machine direction (XD) to account for anisotropy introduced during manufacturing. |
| Preparation | Cut with a die cutter; avoid edge damage; measure thickness at 5 points in the gauge section to ±0.013 mm (±0.001 in) using ASTM D5199/D5994 |
| Conditioning | Precondition at 23±2°C (73±4°F) and 50±5% RH for ≥40 hours before testing |
ASTM D6693 Geomembranes Tensile Strength Test and Elongation Test Equipment required:
Capable of constant crosshead speed (50 mm/min ±10% and 500mm/min); Load measurement accuracy of ±1% of the applied load (per ASTM E4) | |
| Measures elongation with ±0.5% accuracy; gauge length = 50 mm (matching specimen gauge length) | |
| Geomembrane tensile test fixture | Self-tightening or pneumatic grips designed to prevent slippage and crushing of the specimen. |
| Punching machine for sample cutting | For Type IV dumbbell specimens; sharp, precision-ground edges |
ASTM D6693 Geomembranes Tensile Test Procedures (step by step):
| Sample Preparation |
|
| Conditioning | Specimens are conditioned in a standard laboratory atmosphere (e.g., 21°C ± 2°C and 50% ± 10% relative humidity) for a minimum of 40 hours. |
| Mounting | The specimen is mounted in the grips with the long axis aligned with the direction of pull. The extensometer is attached. |
| Testing | The crosshead is set in motion at a constant speed of 50 mm/min (2 in/min). The test continues until the specimen ruptures. ***: The test speed shall be 50 mm/min [2 in./min] for polyethylene geomembranes; 500 mm/min [20 in./min] for nonreinforced flexible polypropylene geomembranes. |
| Data Recording | The force versus elongation (or stress vs. strain) curve is recorded throughout the test. |
Key Properties Determined by ASTM D6693 (Test Application & Output):
The test is applied to determine the following critical engineering properties for material specification, quality control, and conformance testing:
| Tensile Strength at Yield | The stress at which the material first exhibits a constant strain without an increase in stress (the yield point on the curve). |
| Tensile Strength at Break | The stress at the point of rupture. |
| Elongation at Yield | The strain at the yield point. |
| Elongation at Break | The strain at the point of rupture, expressed as a percentage of the original gage length. This is a key measure of ductility. |
| Secant Modulus | A measure of stiffness, calculated as the slope of a line from the origin to a point on the stress-strain curve at a specified strain (e.g., 1% or 2% strain). |
ASTM D6693 relate to other common geomembrane test standards:
ASTM D6693 is part of a suite of tests for a complete geomembrane evaluation. It is the core test for stress-strain properties. Other key tests include:
ASTM D1004 (Tear Resistance): Measures resistance to propagating a tear.
ASTM D4833 (Index Puncture): Measures resistance to localized puncture.
ASTM D5397 (Stress Crack Resistance): Evaluates long-term brittle failure potential (critical for HDPE).
A project specification will typically call for a combination of these tests to get a full picture of mechanical performance.
Primary Applications of standard ASTM D6693:
Manufacturer Quality Assurance (QA): To ensure production batches meet internal specifications.
Project Specification Compliance: Used by engineers, consultants, and owners to verify that supplied geomembrane rolls meet the tensile property requirements outlined in project design specifications (e.g., for landfill liners, reservoirs, or mining pads).
Comparative Material Evaluation: To compare the performance of different geomembrane resins or formulations.
Long-Term Performance Tracking: As part of durability studies, though not an oxidative test itself.
Common applications include:
Landfill liners and caps
Mining tailings ponds
Water/wastewater treatment facilities
Secondary containment systems
Aquaculture ponds
Related products and device
Related Standard
ASTM D6693/D6693M Standard Test Method for Determining Tensile Properties of Nonreinforced Polyethylene and Nonreinforced Flexible Polypropylene Geomembranes
ASTM D6693 is the standard test method for determining the tensile properties of nonreinforced polyethylene and flexible nonreinforced polypropylene geomembranes using dumbbell-shaped specimens under defined pretreatment, temperature, and constant crosshead speed conditionsASTM International. It measures key mechanical properties including yield strength, break strength, yield elongation, break elongation, and modulus of elasticity.
ASTM D1004: Standard Test Method for Tear Resistance (Graves Tear) of Plastic Film and Sheeting
ASTM D1004 is a test method that determines the tear strength of flexible plastic film and sheeting at very low rates of loading using a constant-rate-of crosshead-movement type tensile testing machine. Tearing is produced in a small area of stress concentration of the plastic film or sheeting specimen at controlled speeds below the rate encountered in real world applications in order to produce the most reliable data, which can be used to compare and analyze the tear resistance. Actual use of performance in tearing of certain plastics may not necessarily corralate with the data acquired from this test method. The specimen geometry of this test method produces a stress concentration in a small area of the specimen. The maximum stress, usually found near the onset of tearing, is recorded as the tear resistance in newtons (or pounds-force). The method is not applicable for film or sheeting material where brittle failures occur during testing or where maximum extension is greater than 101.6 mm (4 in.).
Frequently Asked Questions (FAQs) on ASTM D6693: Tensile Testing for Geomembranes
Q1: What is ASTM D6693, and why is it specifically important for geomembranes?
A: ASTM D6693 is the standardized test method for determining the tensile properties of nonreinforced polyethylene (PE) and flexible polypropylene (fPP) geomembranes. It is critically important because geomembranes are used as engineered barriers in vital containment applications like landfills, mining heap leach pads, and water reservoirs. Their tensile strength and elongation are primary indicators of structural integrity and durability. This test provides the key data needed to ensure the material can withstand installation stresses, long-term loading, and subsidence without failing, which is essential for environmental protection and project safety.
Q2: What is the key difference between "Tensile Strength at Yield" and "Tensile Strength at Break," and which is more important?
A:Tensile Strength at Yield: The stress at which the material undergoes a fundamental, irreversible molecular change (necking). Beyond this point, the material is permanently deformed.Tensile Strength at Break: The ultimate stress the material withstands just before rupture.
For geomembranes like HDPE, which are brittle at yield, the Yield Strength is often the critical design property, as it indicates the onset of permanent damage. For more ductile materials like fPP or LLDPE, the Break Strength and the accompanying Elongation at Break are equally important, indicating the material's ability to stretch and redistribute stress before failing.
Q3: Why is the elongation property so critical?
A: High elongation (ductility) is a geomembrane's "forgiveness factor." It allows the liner to:
Conform to subgrade irregularities during installation.
Bridge small cracks or voids in the subgrade.
Accommodate local stress concentrations and settlements without developing a brittle tear. A material with high strength but low elongation is often unsuitable for applications expecting differential settlement.
Q4: What are the common mistakes or challenges when performing this test?
A: Improper Specimen Cutting: Using dull or improper dies can create nicks or micro-tears on the specimen edges, causing premature failure.
Incorrect Gripping: Slippage or excessive crushing at the grips can invalidate results. Proper grip pressure and alignment are crucial.
Not Using an Extensometer: Relying on crosshead travel for strain measurement is inaccurate due to system compliance. An extensometer clamped to the gage section is mandated for accurate elongation data.
Inconsistent Conditioning: Not conditioning specimens in a standard atmosphere (e.g., 23°C, 50% RH) for the required time can lead to variable results, especially for materials sensitive to moisture.
Q5: What types of materials does ASTM D6693 apply to? Can it be used for reinforced geomembranes?
]A: ASTM D6693 is specifically designed for nonreinforced polyolefin geomembranes, including polyethylene (HDPE, LLDPE, LDPE) and flexible polypropylene (PP) geomembranes with thickness ranging from 0.25 mm to 6.3 mm.
It cannot be directly used for reinforced geomembranes (e.g., those with polyester or fiberglass scrims). Reinforced geomembranes require other standards, such as ASTM D4833 (tensile properties of geotextiles) or product-specific test methods that account for the composite structure.
Q6: What if a specimen breaks outside the gauge length during testing? Are the results valid?
A: If a specimen breaks outside the gauge length (e.g., at the grip or shoulder area), the test results for that specimen are invalid and should be discarded.
This failure mode is usually caused by:
Excessive grip pressure that damages the specimen edges.
Poor specimen preparation (e.g., uneven die cutting, burrs at the shoulder).
Improper grip alignment leading to uneven stress distribution.
The standard requires retesting with new specimens until valid results are obtained from the required number of samples (5 per direction).
Q7: What is the difference between ASTM D6693 and the general tensile test standard AST6 D638?
| Aspect | ASTM D6693 | ASTM D638 |
|---|---|---|
| Target Materials | Nonreinforced polyolefin geomembranes | General plastics (thermoplastics, thermosets, composites) |
| Specimen Type | Fixed Type IV dumbbell (gauge length 50 mm, width 13 mm) | Multiple types (I, II, III, IV, V) depending on material |
| Application Scenario | Geotechnical and environmental engineering containment systems | General plastic product quality testing |
| Direction Requirement | Mandatory testing in MD and CD | No mandatory direction requirement unless specified |
Require More Customized Solutions?