Environmental Stress Cracking
Environmental Stress Cracking
Environmental Stress Cracking (ESC) is a phenomenon in which cracks form in a plastic material due to low tensile stress and environmental conditions. This failure occurs when a plastic material, in contact with surface-active substances known as stress cracking agents, becomes brittle at room temperature due to the concurrent presence of external and/or internal stress and strain. Stress-cracking agents include fluids such as alcohols, soaps, dyes, and agents containing moisture, and they can cause cracking when exposed to plastic materials. The amount of time in hours that it takes for half of the specimens tested to exhibit stress cracks is known as Environmental Stress-Cracking Resistance (ESCR).
To measure the ESCR of plastic materials, there are three standard test methods: Condition A, Condition B and Condition C, all of which are outlined in ASTM D 1693. In addition, there are three standard test methods to measure surface cracking: Method A, Method B, and Method C, as outlined in ASTM D 518. Method A involves a straight stretch, Method B involves a bent loop and Method C involves a tapered specimen. In all cases, any cracks that develop in the material constitute failure. Occasionally, cracks may appear beneath the surface and be visible as surface depressions.
