Displacement fields evolution in plain strain grooved tensile (PSGT) specimens during traction and creep loading
Résumé
High Density PolyEthylene (HDPE) is a material widely used for the distribution of drinking water and gas. ISO/TC 138 provides test methods for determining the resistance to internal pressure, due to water flow, which are essential for assessing the properties and durability of thermoplastics piping system parts [1]. These test methods constitute a basis for the determination of short-term and long-term strength characteristics. However, with regard to moulding materials for pipes and fittings, until the publication of the ISO 23228:2011 [2], no satisfactory test method has existed in which the material can be exposed to stress conditions that mimic internally pressurized pipes.
The method specified has been shown to replicate the stress conditions of internally pressurized end-capped pipes by the use of plaque specimen. Plain strain grooved tensile (PSGT) specimens produces a biaxial state of stress on uni-axial loading, which is taken to be indicative of the stress conditions found in pressurized solid-wall plastics pipes. This method is useful for evaluating the stress-rupture resistance of moulding materials and experimental resins being developed for pipes and fittings as well as for those pipes that are difficult to test, such as larger diameter pipes.
In this study, PSGT specimens were cut-out from HDPE pipes. Both the thickness axial and transverse displacements fields were followed with a Digital Image Correlation (DIC) camera during monotonic traction and creep loading. The experimental data observations, under the light of the ISO standard [2], will be discussed.
[1] ISO/TC 138, Thermoplastics pipes, fittings and assemblies for the conveyance of fluids – Determination of the resistance to internal pressure, 1167-1:2006(E), 2006.
[2] ISO/TC 138, Thermoplastics pipes, fittings and assemblies for the conveyance of fluids – Determination of the stress-rupture resistance of moulding materials using plain strain grooved tensile (PSGT) specimens, 23228:2011(E), 2011.