Plastic Pipes Conference Association # 2023 Lake Buena Vista
Dr. Michael Pluimer, Sara Stone
The Notched Constant Ligament Stress test (NCLS test, ASTM F2136)[1] is a test method that measures the slow crack growth in High Density Polyethylene. The NCLS test requires a notch on all test specimens to act as a stress concentration at that point so crack propagation can be easily predicted and studied. In addition to the notch, the NCLS test requires a test bath solution of “...10 % non-ylphenoxy poly (ethyleneoxy) ethanol by volume in 90 % deionized water”[1] to be heated and held at 50°C during the test procedure. The detergent present in the aqueous mixture, when held at an elevated temperature, acts as a crack accelerant, leading to relatively short test times (<1000 hours). The shortened test times are beneficial to pipe manufacturers conducting quality assurance checks on their products.
There have been ongoing investigations into developing a cyclic fatigue test to emulate the results of the NCLS test in less time. This test method could be developed into an additional quality control check to more quickly assess the SCR of HDPE so that pipe manufacturers can more efficiently develop and qualify various materials. The primary goal of this research is to develop a new accelerated test method for assessing the SCR of HDPE materials correlating with the NCLS test but have considerably shorter failure times, making it more useful for a quality control test. The research investigates a new dynamic accelerated fracture test being conducted on notched specimens similar to those used in the NCLS test.
Recent announcements suggest that the manufacturing of Igepal, a common detergent used in the NCLS test bath solution, will cease within the near future (official date-to-bedetermined), leading to the imminent development of an alternative test solution. A secondary goal of this research is to produce similar results to the current NCLS test method using only deionized water as the test bath solution, and thereby propose an additional test method to be included in the current NCLS test standard. This research is currently underway and will establish a correlation between the current detergentcontaining NCLS test method and the proposed additional alternatives, therefore substantiating the possibility of using a purely deionized water bath as an alternative testing option during NCLS stress crack testing and employing the cyclic fatigue test as a quality control test to be used in conjunction with the current NCLS test standard.
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