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Modeling the performance and failure of elastomeric coatings under erosive cavitating flows

Description

Finite element simulations modeling the hydrodynamic impact loads subjected to an elastomeric coating were performed to develop an understanding of the performance and failure mechanisms of protective coatings for cavitating

Finite element simulations modeling the hydrodynamic impact loads subjected to an elastomeric coating were performed to develop an understanding of the performance and failure mechanisms of protective coatings for cavitating environments.

In this work, two major accomplishments were achieved: 1) scaling laws were developed from hydrodynamic principles and numerical simulations to allow conversion of measured distributions of pressure peaks in a cavitating flow to distributions of microscopic impact loadings modeling individual bubble collapse events, and 2) a finite strain, thermo-mechanical material model for polyurea-based elastomers was developed using a logarithmic rate formulation and implemented into an explicit finite element code.

Combining the distribution of microscopic impact loads and finite element modeling, a semi-quantitative predictive framework is created to calculate the energy dissipation within the coating which can further the understanding of temperature induced coating failures.

The influence of coating thickness and elastomer rheology on the dissipation of impact energies experienced in cavitating flows has also been explored.

The logarithmic formulation has many desired features for the polyurea constitutive model, such as objectivity, integrability, and additive decomposition compatibility.

A review and discussion on the kinematics in large deformation, including a comparison between Lagrangian and Eulerian descriptions, are presented to explain the issues in building rate-dependent constitutive models in finite strains.

When comparing the logarithmic rate with other conventional rates in test examples, the logarithmic rate shows a better conservation of objectivity and integrability.

The modeling framework was validated by comparing predictions against temperatures measured within coatings subjected to a cavitating jet.

Both the experiments and models show that the temperatures generated, even under mild flow conditions, raise the coating temperature by a significant amount, suggesting that the failure of these coatings under more aggressive flows is thermally induced.

The models show that thin polyurea coatings synthesized with shorter molecular weight soft segments dissipate significantly less energy per impact and conduct heat more efficiently.

This work represents an important step toward understanding thermally induced failure in elastomers subjected to cavitating flows, which provides a foundation for design and optimization of coatings with enhanced erosion resistance.

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Date Created
  • 2016

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The integrity of geosynthetic elements of waste containment barrier systems subject to seismic loading

Description

A method for evaluating the integrity of geosynthetic elements of a waste containment system subject to seismic loading is developed using a large strain finite difference numerical computer program. The

A method for evaluating the integrity of geosynthetic elements of a waste containment system subject to seismic loading is developed using a large strain finite difference numerical computer program. The method accounts for the effect of interaction between the geosynthetic elements and the overlying waste on seismic response and allows for explicit calculation of forces and strains in the geosynthetic elements. Based upon comparison of numerical results to experimental data, an elastic-perfectly plastic interface model is demonstrated to adequately reproduce the cyclic behavior of typical geomembrane-geotextile and geomembrane-geomembrane interfaces provided the appropriate interface properties are used. New constitutive models are developed for the in-plane cyclic shear behavior of textured geomembrane/geosynthetic clay liner (GMX/GCL) interfaces and GCLs. The GMX/GCL model is an empirical model and the GCL model is a kinematic hardening, isotropic softening multi yield surface plasticity model. Both new models allows for degradation in the cyclic shear resistance from a peak to a large displacement shear strength. The ability of the finite difference model to predict forces and strains in a geosynthetic element modeled as a beam element with zero moment of inertia sandwiched between two interface elements is demonstrated using hypothetical models of a heap leach pad and two typical landfill configurations. The numerical model is then used to conduct back analyses of the performance of two lined municipal solid waste (MSW) landfills subjected to strong ground motions in the Northridge earthquake. The modulus reduction "backbone curve" employed with the Masing criterion and 2% Rayleigh damping to model the cyclic behavior of MSW was established by back-analysis of the response of the Operating Industries Inc. landfill to five different earthquakes, three small magnitude nearby events and two larger magnitude distant events. The numerical back analysis was able to predict the tears observed in the Chiquita Canyon Landfill liner system after the earthquake if strain concentrations due to seams and scratches in the geomembrane are taken into account. The apparent good performance of the Lopez Canyon landfill geomembrane and the observed tension in the overlying geotextile after the Northridge event was also successfully predicted using the numerical model.

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Date Created
  • 2011