Environmental Stress-Cracking Resistance (ESCR) - ASTM D1693
Environmental stress cracking is the formation of cracks in a material caused by relatively low tensile stress and environmental conditions. Environmental Stress-Cracking Resistance (ESCR) is the number of hours that 50% of the specimens tested exhibit stress cracks.
ESCR testing is performed by slowly bending the test specimens and placing them in a holding clamp. The clamp and specimens are then placed in a test tube and immersed in a specified reagent. The test tube is sealed and placed in a constant-temperature bath. Multiple test specimens are tested at one time.
ESCR Specimens in Holder
Specimens are inspected periodically for failure. Cracks generally develop at the notch, perpendicular to the notch, and run to the edge of the specimen. Any cracks constitute failure, not just cracks that reach the edge of the specimen. Cracks sometimes appear beneath the surface and are visible as surface depressions. If a depression develops into a surface crack the time at which the depression was noted is taken as the time of failure.
Three test conditions are specified. Condition A is generally used for polyethylene with densities between 0.910 and 0.925 g/cm³. Condition B is used for polyethylene with densities greater than 0.925 g/cm³. Condition C is used for accelerated testing of materials with extremely high ESCR values.
A summary of the differences in the different test conditions is listed below.
|Condition||Thickness (mm)||Notch Depth (mm)||Bath Temperature (°C)|