Plastic Pipes Conference Association # 2021 Amsterdam
Britta Gerets, Mirko Wenzel, Kurt Engelsing
The strain hardening test (SHT, ISO 18488 [1]) becomes increasingly important for the characterization of high-density polyethylene (HDPE) grades and pipes made thereof. With regard to small pipe diameters, a smaller test specimen than the one defined in ISO 18488 has been developed. SHT results were demonstrated to remain unchanged as long as the applied strain rate stays constant. With a succession of sawing, milling, grinding and finally punching, a procedure to extract specimens from pipes was developed. [2] In further work the procedure was optimized: Thin films, from which dogbone specimen can be punched directly, were generated on a lathe. This provides the additional benefit that specimens can also be extracted in circumferential direction. A variety of different HDPE pipe grades and pipe dimensions were tested and the SHT results were put in relation to those from material tests according to ISO 18488. Although the same material batch was used in both cases, differences between material and pipe test results were observed. [3] Therefore, the influences of pipe dimension and the pipe extrusion process were studied. Especially molecular orientation revealed a great impact on the SHT results.
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