Numerical Modeling of Stress Corrosion Cracking in Polymers
2015-12
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Numerical Modeling of Stress Corrosion Cracking in Polymers
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2015-12
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Polymeric materials have been increasingly used for structural purposes in civil infrastructures. However, stress corrosion cracking has been a critical issue that affects the service lifetime of polymer components. My preliminary study showed that polyethylene may be severely corroded in an oxidizing environment and lose its fracture resistance property. Experimental methods have been primarily adopted to investigate stress corrosion cracking in polymers; however, these approaches are expensive to apply, and may fail to account for certain aspects of this chemo-mechanical process. Therefore, a numerical approach is needed to investigate this issue. A unified chemo-mechanical model is developed to predict the stress corrosion cracking (SCC) of a viscoplastic polymer. This model is applied to the specific case of high density polyethylene (HDPE) exposed to a chlorinated environment at a constant stress load. This chemo-mechanical model is comprised of three components, each capturing a critical aspect of SCC. An elastic-viscoplastic constitutive model is adopted to predict the time-dependent creep behavior of HDPE, and the model parameters have been calibrated through tensile testing. This constitutive model has been implemented in finite element analysis by using a user-defined material subroutine. The polymer fracture property is considered to be dependent on the extent of corrosion, and this dependence is implemented with a cohesive zone model. A chemical kinetics and diffusion model is utilized to predict the degradation of fracture properties in the material as a result of reactions and migration of chemical substances. The coupled chemo-mechanical simulation is accomplished by integrating the chemical reaction calculation into finite element analysis via user defined subroutines. Two modes are considered for failure of the polymer: excessive plastic deformation or catastrophic unstable crack growth. At high stresses, the failure is primarily due to excessive plastic deformation. At low stresses, chemical reactions and diffusion are the dominant factors leading to failure. In addition, two distinct patterns of crack growth (reaction-driven or diffusion-driven) are revealed at various disinfectant concentrations at low stress levels. In reaction-driven crack growth, material degradation is localized at the crack tip, and crack growth rate is a constant throughout the simulated lifetime. However, when diffusion dominates, the entire specimen ligament may be severely degraded, and crack growth accelerates at the end of component lifetime. The current simulation framework allows exploring the interaction of various factors in stress corrosion cracking, such as disinfectant concentration, loading, and temperature. The framework is also general enough to be implemented for other polymeric materials and corresponding corrosion mechanisms. In the future, the proposed chemo-mechanical modeling approach may be expanded to analyze the performance of a variety of materials under stress corrosion cracking. In addition, a stochastic methodology may be incorporated to account for the variances in loading, as well as material properties.
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University of Minnesota Ph.D. dissertation. December 2015. Major: Mechanical Engineering. Advisors: Susan Mantell, Jia-Liang Le. 1 computer file (PDF); xi, 89 pages.
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Ge, Hanxiao. (2015). Numerical Modeling of Stress Corrosion Cracking in Polymers. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/177169.
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