Chapter 6 Mechanical Characterization and Numerical Modeling of High Density Polyethylene Pipes Mehrzad Taherzadehboroujeni and Scott W. Case Abstract The worldwide plastic pipe industry is predicted to experience a dramatic grow over the next decade. As a group of plastic pipes, high density polyethylene (HDPE) pipes are often employed because of their low-cost production, easy installation, and excellent long-term performance. However, due to their complicated semi-crystalline microstructure and nonlinear time-temperature dependent mechanical behavior, the mechanical characterization of HDPE pipes is very challenging and time consuming. In addition, during the manufacturing of HDPE pipes, the processing conditions (such as molecular orientation, cooling rate, and extrusion injection pressure) can introduce different complex microstructures into the material which yield different material properties. In this study, a robust mechanical characterization approach is developed to support numerical modeling of HDPE pipes. The mechanical tests are performed directly on as-manufactured pipe segments. The simulation results are compared with the experimental data for tensile and internal pressurization (burst) tests and a good agreement is observed. Keywords Long-term hydrostatic strength · HDPE pipe characterization · Numerical modeling · Accelerated method 6.1 Introduction Thanks for their excellent features such as low cost of manufacturing, low density and easy installation, polymeric pipes have been widely employed in pressure vessel networks and pipelines. However, because of their complicated time-temperature dependent behavior of polymeric materials, understanding and predicting the long-term performance of the pipes are challenging. In particular, the long-term performance and the lifetime of these pipes are dramatically sensitive to the loading level and the working temperature. The challenge can become even greater when the pipes are used in applications with a variable environmental condition such as temperature and/or in a pipe network with load variations. In terms of safety and required standards, the plastic pipes should be designed to have at least 50 years lifetime under a specified loading level. Therefore, investigations are needed to evaluate the long-term performance of the pipes and insure the quality of new designed products. Recently, a number of studies have been conducted focusing on the long-term creep behavior of polymeric materials. Hu et al. [1] investigated the impacts of temperature and stress on the short-term and long-term creep behavior of ethylene tetrafluoroethylene (ETFE). They found that the time-temperature superposition could underestimate the creep strains while the time-stress superposition could overestimate creep strains. Zhou et al. [2] experimentally studied the creep behavior and lifetime performance of PMMA immersed in liquid scintillator. The comparison between the proposed model perditions and actual long-term creep results demonstrate excellent agreement for short time data, However, the actual creep data shows a higher creep rate for long-time data. The effects of size and thickness on the creep property of a cross-linked polyethylene were studied by Takahashi et al. [3]. In addition, several studies conducted to understand the long term creep behavior in plastic pipes. Fatima et al. [4] investigated the differences between the burst behavior of chlorinated polyvinyl chloride (CPVC) and high density polyethylene pipes. In a different study, Moon et al. [5] suggested two algorithmic methods to construct the long-term strength estimation line of plastic pipes. The methods eliminate uncertainties and errors caused by the typical trial and error approach M. Taherzadehboroujeni ( ) · S. W. Case Department of Biomedical Engineering and Mechanics, Virginia Tech, Blacksburg, VA, USA e-mail: mehrzadt@vt.edu S.W. Case Macromolecules Innovation Institute, Virginia Tech, Blacksburg, VA, USA © Society for Experimental Mechanics, Inc. 2020 A. Linderholt et al., Dynamic Substructures, Volume 4, Conference Proceedings of the Society for Experimental Mechanics Series, https://doi.org/10.1007/978-3-030-12184-6_6 57
RkJQdWJsaXNoZXIy MTMzNzEzMQ==