Effects of Crosshead Speed on the Quasi-Static Stress-Strain Relationship of Polyethylene Pipes

Quasi-static stress-strain relationship of polyethylene ( PE) pressure pipe that plays an important role on its long-term performance has been established by removing the viscous stress component from the experimentally measured total stress. Work reported here is focused on the influence of crosshead speed on the notched pipe ring (NPR) specimens that are prepared from PE pressure pipe of 2 in. in diameter. Viscous component of the stress-strain relationship was determined using a spring-damper-plastic element model, calibrated using results from stress relaxation tests. Crosshead speeds considered for the initial stretch of the stress relaxation tests are 0.01, 1, and 10 mm/min which due to the relatively uniform deformation in the gauge section generate the same order of difference in the strain rates. Results from the study suggest that the quasi-static stress-strain relationship is affected by the crosshead speed used to generate the deformation, and the trend of change is opposite to the total stress counterpart that includes the viscous component.