【国外标准】 Standard Test Method for Notch Tensile Test to Measure the Resistance to Slow Crack Growth of Polyethylene Pipes and Resins

5.1 This test method is useful to measure the slow crack growth resistance of molded plaques of polyethylene materials at accelerated conditions such as 80 °C, 2.4 MPa stress, and with a sharp notch.5.2 The testing time or time to failure depends on the following test parameters: temperature; stress; notch depth; and specimen geometry. Increasing temperature, stress, and notch depth decrease the time to failure. Material parameters, not controlled by the laboratory, that could impact the test results (time to failure) are: pigment (color or carbon black) and the carrier resin for the pigment, or both. Thus, in reporting the test time or time to failure, all the conditions of the test shall be specified.NOTE 4: Time to failure can also be affected by the degree of pigment (color or carbon black) dispersion and distribution within the test specimen. Test Method D5596 and ISO 18553 provide methods for assessing the degree of dispersion and distribution of the pigment1.1 This test method determines the resistance of polyethylene materials to slow crack growth under conditions specified within.NOTE 1: This test method is known as PENT (Pennsylvania Notch Test) test.1.2 The standard test is performed at 80 °C and at 2.4 MPa, but it shall be acceptable to conduct tests at a temperature below 80 °C and with other stresses low enough to preclude ductile failure and thereby eventually induce brittle type of failure. The standard test is conducted in an air environment; however, it shall be acceptable to immerse test specimens in an alternate environment such as water or a water/detergent solution, or other liquid or a different environment such as an inert gas to evaluate slow crack growth performance in different environments. Generally, polyethylenes will ultimately fail in a brittle manner by slow crack growth at 80 °C if the stress is at or below 2.4 MPaNOTE 2: When testing in environments other than air, it is recommended to consider maintaining the efficacy of the test media (for example, a detergent solution) to minimize any effect of aging.1.3 The test method is for specimens cut from compression molded plaques.2 See Appendix X1 for information relating to specimens from pipe.1.4 The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for information only and are not considered standard.1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.