New Test Method for Measurement of Strain Hardening Modulus on Polyethylene Materials used in the Manufacture of Stress-Rated Pipe
1. Scope
This test method uses tensile testing to measure the strain hardening modulus from the stress-strain curve above the natural draw ratio on stress-rated polyethylene materials intended for pipe manufacturing. The intent of this test method is to use the measured value of strain hardening modulus to provide information about the slow crack growth resistance on compression molded samples of polyethylene materials and compounds without establishing any acceptance criteria for use in pressure piping applications. Nevertheless, this test method does allow for discrimination between materials. This test method describes in detail the preparation of samples for testing, establishes conditions for the conduct of cross-head displacement testing and stress / strain measurement and provides instructions on how values obtained from such measurements are used in the calculation of the strain hardening modulus.
Keywords
Stress crack resistance of materials
Rationale
Bryan Hauger previously had a project authorized in November 2016 to create a new test method at ASTM F17.40 as WK56413 following a presentation to a task group at that November 2016 meeting. After one subcommittee ballot, that project was dropped. The rationale for the project at the time was “Strain Hardening Modulus above the Natural Draw Ratio has been widely discussed for its capability to provide insights into the slow-crack growth (SCG) performance of polyethylene materials. Tremendous reduction in the amount of time required to complete testing in this tensile test method in comparison with other widely practiced SCG test methods”.
