ASTM D1693-00 Standard Test Method for Environmental Stress Cracking of Ethylene Plastics

The standard "ASTM D1693-00 Standard test method for environmental stress cracking of ethylene plastics" developed by the American Society for Testing and Materials (ASTM) describes a test method for determining the susceptibility of ethylene plastics to environmental stress cracking when subjected to the conditions specified therein, as defined in the standard "ASTM D883-23 Standard Terminology for Plastics". Under certain stress conditions and in the presence of media such as soaps, wetting agents, oils or detergents, ethylene plastics may exhibit mechanical failure by cracking.

For the purposes of this standard, the following terms and definitions apply:

• A stress crack is an external or internal rupture in a plastic caused by tensile stresses lower than its short-term mechanical strength. The development of such cracks is often accelerated by the environment to which the plastic is exposed. The stresses that cause the crack may be internal or external, or a combination of these stresses. The appearance of a network of fine cracks is called cracking.
• Stress crack failure, for the purposes of this test method, shall be interpreted as failure of the entire specimen, any crack visible to an observer with normal vision. Extension of the controlled flaw shall not be interpreted as failure. The appearance of more than one crack in a single specimen shall be interpreted as a single failure. Cracks generally develop in controlled flaws and extend approximately at right angles to the outer edge of the specimen. Cracks do not have to extend through the entire specimen to cause failure. Cracks sometimes develop below the polymer surface and present themselves as depressions in the surface. It shall be noted when this occurs and if the depression later develops into a crack, the time to failure shall be considered.

When performing the test, bent plastic samples, each with a controlled defect on one surface, are exposed to the action of a surfactant. The rate of total number of samples cracking in a given time is observed.

This test method can be used for routine inspection purposes by subjecting the required number of samples to the test conditions for a specified period of time and noting the number that fail. The cracking obtained with the test reagent is indicative of what can be expected from a wide range of surfactants, soaps and organic substances that are not significantly absorbed by the polymer.

Environmental stress cracking is a property that is highly dependent on the nature and level of applied stresses and the thermal history of the specimen. Under the conditions of the test method, high local multiaxial stresses develop through the introduction of a controlled flaw. Environmental stress cracking has been found to occur most readily under such conditions.

The different types of polyethylene plastics defined in the standard "ASTM D1248-12 Standard Specification for Polyethylene Plastic Extrusion Materials for Wire and Cable" are generally tested under different stress and strain levels. When it is explicitly desired to compare types at equal stress levels, specimens for all types shall be tested under Condition B in the table provided in the standard.

The information obtained from this test method is not intended to be applied directly to engineering problems. Care should be taken when classifying and ranking the various ethylene plastics into distinct and separate groups using this test method.

Because thermal history is considered an important variable, test results obtained by this test method using laboratory molded samples cannot be expected to agree with test results obtained from samples obtained by other means. However, the true performance potential of a particular ethylene plastic can best be determined by samples obtained from commercially prepared products.

The main equipment used in these tests includes: cutting die, fixture, sample holders, test tubes, corkscrews, aluminum foil, constant temperature bath, test tube rack, bending clamp, and transfer tool. The test reagent may be a surfactant, soap, or any liquid organic substance that is not significantly absorbed by the polymer.

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