ASTM D6387: Testing Coated Flexible Packaging — Procedure Explained
What Is ASTM D6387?
ASTM D6387 — Standard Test Method for Characteristics of Multi-Axially Stressed Polyolefin Geomembranes — evaluates the resistance of polyolefin geomembrane sheets to stress cracking when subjected to simultaneous biaxial and shear stresses representative of the complex loading conditions experienced by geomembranes in field installations. This test is part of the comprehensive qualification testing battery used for geomembranes in containment applications including landfill liners, pond liners, and tailings impoundments.
Why Multi-Axial Stress Cracking Testing Is Important for Geomembranes
Polyolefin geomembranes — particularly high-density polyethylene (HDPE) — are susceptible to stress cracking (environmental stress cracking, ESC) when subjected to sustained tensile stress in the presence of surface-active agents, chemicals in the contained waste, or even the soil/leachate contact environment. Stress cracking causes premature brittle failure at stresses far below the short-term tensile strength — a critical concern for containment performance over the 30–100+ year design life of landfill liners.
Multi-axial stress cracking testing evaluates ESC resistance under loading geometries more representative of field conditions than uniaxial tests.
ASTM D6387 Test Procedure
Specimen Preparation
Geomembrane specimens are cut from the production roll in both machine direction (MD) and transverse direction (TD). Specimens may be tested as received or after notching to create defined stress concentration zones that accelerate stress cracking initiation.
Test Fixture
The multi-axial stress apparatus simultaneously applies biaxial and shear stresses to the specimen — stressing the geomembrane in a geometry that represents the combined tension, bending, and shear loads at liner anchor trench transitions, slope interfaces, and penetration details.
Stress Cracking Environment
The stressed specimens are immersed in a defined stress cracking agent — typically Igepal CO-630 (nonylphenyl polyethylene glycol) at elevated temperature (50°C) — that promotes ESC without significantly affecting the bulk material properties. The surface-active agent reduces the critical stress intensity for crack initiation, accelerating the test.
Test Duration and Evaluation
Specimens are monitored at defined intervals for crack initiation and propagation. The test is run until a defined percentage of specimens have cracked or a maximum test duration is reached. Results are reported as time to failure distribution — longer times to cracking indicate better ESC resistance.
Relationship to Other Geomembrane Stress Cracking Tests
ASTM D6387 is one of several geomembrane stress cracking evaluations used in qualification programmes:
- ASTM D5397 (SP-NCTL test): Single-point notched constant tensile load — the most widely specified geomembrane ESC test, providing failure time at defined stress level
- ASTM D5885 (Multi-axial tension creep): Long-term multi-axial tension under elevated temperature
- ASTM D6693 (Notched Constant Tensile Load, NCTL): Full-panel NCTL with multi-point loading
Together, these methods characterise different aspects of ESC behaviour to ensure geomembrane durability in containment applications.
Industrial Applications
HDPE geomembranes are used in municipal solid waste landfill bottom liners (required by EPA Subtitle D and Subtitle C regulations), mining heap leach pads, coal ash impoundments, water storage reservoirs, and secondary containment systems for hazardous materials. All applications require demonstration of adequate ESC resistance through standardised testing programmes.
Why Choose Infinita Lab for Geomembrane Testing?
Infinita Lab provides ASTM D6387, ASTM D5397, and comprehensive geomembrane qualification testing through our nationwide accredited geosynthetics testing laboratory network, supporting landfill liner and containment system qualification.
Looking for a trusted partner to achieve your research goals? Schedule a meeting with us, send us a request, or call us at (888) 878-3090 to learn more about our services and how we can support you.
Frequently Asked Questions (FAQs)
What is environmental stress cracking (ESC) in HDPE geomembranes? ESC is brittle fracture of HDPE under sustained tensile stress in the presence of surface-active agents that reduce the critical stress intensity for cracking — causing failure at stresses far below short-term tensile strength. It is the primary long-term durability concern for HDPE geomembrane containment systems.
Why is elevated temperature used in ASTM D6387 testing? Elevated temperature (typically 50°C) accelerates ESC kinetics by increasing polymer chain mobility and enhancing penetration of the stress cracking agent — reducing test duration from potentially years at ambient temperature to weeks in the accelerated test. Arrhenius modelling extrapolates accelerated test data to ambient temperature service life.
What is the difference between ASTM D5397 and ASTM D6387 for geomembrane stress cracking? ASTM D5397 (SP-NCTL) applies uniaxial constant tensile load to notched strip specimens — the most reproducible, widely specified single-point ESC test. ASTM D6387 applies multi-axial stress states — more representative of complex field loading at anchors and slope transitions. Both are used in comprehensive qualification programmes.
What minimum performance is typically required for HDPE geomembrane ESC resistance? GRI GM13 (Geosynthetics Research Institute HDPE geomembrane specification) requires minimum NCTL failure time of 200 hours at 30% yield stress with Igepal CO-630 per ASTM D5397 for standard service 60 mil HDPE geomembranes. More critical applications (landfill leachate containment) may require 400–1000+ hours.
Can stress cracking be detected non-destructively in installed geomembranes? Visual inspection (ultraviolet light, optical magnification) can detect surface stress cracking on exposed geomembrane areas. Electrical leak location (ELL) methods detect through-thickness defects by electrical conductance between the liner and underlying substrate. Destructive core sampling followed by laboratory ESC testing provides condition assessment for aged geomembranes in service.
