Abstract
This paper describes the applicability of a new quality control test method, the full-notch tensile fatigue (FNTF) test, using fatigue behavior. As quality control test methods for PE pipes, stress rupture tests, environmental stress crack resistance tests (ESCR tests), etc. for testing long-term strength have been conducted, all of which are prescribed in the JIS. However, as the time to failure is extremely long in these tests, quality is not judged by the actual time to failure but is judged acceptable if the time exceeds a certain limit. To accelerate failure, the FNTF test was proposed, in which the test specimen is notched all around and a repetitive load is applied to it. The significance of this test was studied. The test, conducted with a square wave in a complete tension mode at an elevated temperature of 80°C and at a frequency of 0.5Hz, enables practical and efficient quality control of polyethlene pipes. In this test method, failure is accelerated to about 1/100 of the time specified for the stress rupture test in the JIS, and it is possible to determine a failure curve, from which the change in the performance of a resin product by an actual time to failure can be determined. From the test result, it has been shown that the time to failure due to pure creep can be predicted by studying the creep-fatigue interaction at various frequencies.
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