Publications

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Polymer foam encapsulants provide mechanical, electrical, and thermal isolation in engineered systems. In fire environments, gas pressure from thermal decomposition of polymers can cause mechanical failure of sealed systems. A 3-D finite element conduction-radiation model with porous media flow and a chemistry model was created to investigate the heat transfer and pressurization in such scenarios. Experiments show that the rate of pressurization and the temperature of select thermocouples are dependent on orientation with respect to gravity, indicating buoyancy-driven flow. In this work, the gas velocity is solved by applying the Darcy approximation, and the heat transfer and pressurization are determined by solving the continuity, species, and enthalpy equations in the condensed and gas phases. This work will describe the porous media model, explore material parameters (e.g. phase, permeability, conductivity) for use with PMDI polyurethane, compare predictions to experimental data, and recommend values for material properties. It will use multiple heating rates to validate the data, and show that incorporating gas motion into the model captures the divergent nature of the results in different orientations.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Polymer foam encapsulants provide mechanical, electrical, and thermal isolation in engineered systems. It can be advantageous to surround objects of interest, such as electronics, with foams in a hermetically sealed container in order to protect them from hostile environments or from accidents such as fire. In fire environments, gas pressure from thermal decomposition of foams can cause mechanical failure of sealed systems. In this work, a detailed uncertainty quantification study of polymeric methylene diisocyanate (PMDI)-polyether-polyol based polyurethane foam is presented and compared to experimental results to assess the validity of a 3-D finite element model of the heat transfer and degradation processes. In this series of experiments, 320 kg/m3 PMDI foam in a 0.2 L sealed steel container is heated to 1,073 K at a rate of 150 K/min. The experiment ends when the can breaches due to the buildup of pressure. The temperature at key location is monitored as well as the internal pressure of the can. Both experimental uncertainty and computational uncertainty are examined and compared. The mean value method (MV) and Latin hypercube sampling (LHS) approach are used to propagate the uncertainty through the model. The results of the both the MV method and the LHS approach show that while the model generally can predict the temperature at given locations in the system, it is less successful at predicting the pressure response. Also, these two approaches for propagating uncertainty agree with each other, the importance of each input parameter on the simulation results is also investigated, showing that for the temperature response the conductivity of the steel container and the effective conductivity of the foam, are the most important parameters. For the pressure response, the activation energy, effective conductivity, and specific heat are most important. The comparison to experiments and the identification of the drivers of uncertainty allow for targeted development of the computational model and for definition of the experiments necessary to improve accuracy.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

We report measurements of temperature and O2/N2 mole-fraction ratio in the vicinity of a burning and decomposing carbon-epoxy composite aircraft material samples exposed to uniform heat fluxes of 48 and 69 kW/m2. Controlled laboratory experiments were conducted with the samples suspended above a cone-type heater and enclosed in an optically accessible chimney. Noninvasive coherent anti-Stokes Raman scattering (CARS) measurements we performed on a single-laser-shot basis. The CARS data were performed with both a traditional point measurement system and with a one-dimensional line imaging scheme that provides single-shot temperature and O2/N2 profiles to reveal the quantitative structure of the temperature and oxygen concentration profiles over the duration of the 30-40 minute duration events. The measured near-surface temperature and oxygen transport are an important factor for exothermic chemistry and oxidation of char materials and the carbon fibers themselves in a fire scenario. These unique laser-diagnostic experiments provide new information on physical/chemical processes in a well-controlled environment which may be useful for the development of heat-and mass-transfer models for the composite fire scenario.

Abstract not provided.

Thermal analysts address a wide variety of applications requiring the simulation of radiation heat transfer phenomena. The re are gaps in the currently available modeling capabilities. Addressing these gaps w ould allow for the consideration of additional physics and increase confidence in simulation predictions. This document outlines a five year plan to address the current and future needs of the analyst community with regards to modeling radiation heat tran sfer processes. This plan represents a significant multi - year effort that must be supported on an ongoing basis.

Abstract not provided.

Abstract not provided.

Abstract not provided.

TDI foams of nominal density from 10 to 45 pound per cubic foot were decomposed within a heated stainless steel container. The pressure in the container and temperatures measured by thermocouples were recorded with each test proceeding to an allowed maximum pressure before venting. Two replicate tests for each of four densities and two orientations in gravity produced very consistent pressure histories. Some thermal responses demonstrate random sudden temperature increases due to decomposition product movement. The pressurization of the container due to the generation of gaseous products is more rapid for denser foams. When heating in the inverted orientation, where gravity is in the opposite direction of the applied heat flux, the liquefied decomposition products move towards the heated plate and the pressure rises more rapidly than in the upright configuration. This effect is present at all the densities tested but becomes more pronounced as density of the foam is decreased. A thermochemical material model implemented in a transient conduction model solved with the finite element method was compared to the test data. The expected uncertainty of the model was estimated using the mean value method and importance factors for the uncertain parameters were estimated. The model that was assessed does not consider the effect of liquefaction or movement of gases. The result of the comparison is that the model uncertainty estimates do not account for the variation in orientation (no gravitational affects are in the model) and therefore the pressure predictions are not distinguishable due to orientation. Temperature predictions were generally in good agreement with the experimental data. Predictions for response locations on the outside of the can benefit from reliable estimates associated with conduction in the metal. For the lighter foams, temperatures measured on the embedded component fall well with the estimated uncertainty intervals indicating the energy transport rate through the decomposed region appears to be accurately estimated. The denser foam tests were terminated at maximum allowed pressure earlier resulting in only small responses at the component. For all densities the following statements are valid: The temperature response of the embedded component in the container depends on the effective conductivity of the foam which attempts to model energy transport through the decomposed foam and on the stainless steel specific heat. The pressure response depends on the activation energy of the reactions and the density of the foam and the foam specific heat and effective conductivity. The temperature responses of other container locations depend heavily on the boundary conditions and the stainless steel conductivity and specific heat.

Polymer foam encapsulants provide mechanical, electrical, and thermal isolation in engineered systems. In fire environments, gas pressure from thermal decomposition of polymers can cause mechanical failure of sealed systems. In this work, a detailed uncertainty quantification study of PMDI-based polyurethane foam is presented to assess the validity of the computational model. Both experimental measurement uncertainty and model prediction uncertainty are examined and compared. Both the mean value method and Latin hypercube sampling approach are used to propagate the uncertainty through the model. In addition to comparing computational and experimental results, the importance of each input parameter on the simulation result is also investigated. These results show that further development in the physics model of the foam and appropriate associated material testing are necessary to improve model accuracy.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

New aircraft are being designed with increasing quantities of composite materials used in their construction. Different from the more traditional metals, composites have a higher propensity to burn. This presents a challenge to transportation safety analyses, as the aircraft structure now represents an additional fuel source involved in the fire scenario. Performance testing data for composites burning in a fire at the integral scales of an accident event are nearly non-existent. This report describes fire tests for relevant carbon fiber epoxy materials that were designed to explore the bulk decomposition behavior of said material in a severe fire. Together with TGA decomposition data, the material is found to decompose in three mostly distinctive and sequential phases, epoxy pyrolysis, char oxidation, and carbon fiber oxidation. Fires were not severe in their thermal intensity compared to liquid fuel fires. Peak thermal intensities of around 220 kW/m2 or 1100 °C are achieved at very low air flow rates. The burn tests were remarkable in their duration, lasting 4-8 hours for 25-40 kg of combustible material.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

The behavior of carbon fiber aircraft composites was studied in adverse thermal environments. The effects of resin composition and fiber orientation were measured in two test configurations: 102 by 127 millimeter (mm) test coupons were irradiated at approximately 22.5 kW/m{sup 2} to measure thermal response, and 102 by 254 mm test coupons were irradiated at approximately 30.7 kW/m{sup 2} to characterize piloted flame spread in the vertically upward direction. Carbon-fiber composite materials with epoxy and bismaleimide resins, and uni-directional and woven fiber orientations, were tested. Bismaleimide samples produced less smoke, and were more resistant to flame spread, as expected for high temperature thermoset resins with characteristically lower heat release rates. All materials lost approximately 20-25% of their mass regardless of resin type, fiber orientation, or test configuration. Woven fiber composites displayed localized smoke jetting whereas uni-directional composites developed cracks parallel to the fibers from which smoke and flames emanated. Swelling and delamination were observed with volumetric expansion on the order of 100% to 200%. The purpose of this work was to provide validation data for SNL's foundational thermal and combustion modeling capabilities.

Abstract not provided.

Polymer foam encapsulants provide mechanical, electrical, and thermal isolation in engineered systems. In fire environments, foams, such as polyurethanes, can liquefy and flow during thermal decomposition, and evolved gases and vapors can cause pressurization and failure of sealed containers. Liquefaction and flow of decomposing foam can cause serious modeling issues in systems safety and hazard analyses. To mitigate the issues resulting from liquefaction and flow, a hybrid polyurethane-cyanate-ester-epoxy foam was developed that has mechanical properties similar to currently used polyurethane foams. The hybrid foam behaves predictably, does not liquefy, and forms 40-50 percent by weight uniform char during decomposition in nitrogen. The char forms predictably and is a relatively uniform "participating medium." A previous paper discussed the experimental and modeling approach developed to predict radiation and conduction heat transfer through decomposing hybrid foam in vented containers. This paper discusses application of a similar approach to the more difficult problem of predicting heat transfer, foam decomposition, and pressure growth in sealed containers. Model predictions are compared with results from radiant heat transfer experiments involving foam encapsulated objects in sealed containers. All model parameters were evaluated from independent laboratory-scale experiments such as TGA and DSC. The time dependent-pressure in the container and the timedependent temperature near the surface of a foam-encapsulated object agreed well with experimental data. © (2010) by BCC Research All rights reserved.

Composite materials behave differently from conventional fuel sources and have the potential to smolder and burn for extended time periods. As the amount of composite materials on modern aircraft continues to increase, understanding the response of composites in fire environments becomes increasingly important. An effort is ongoing to enhance the capability to simulate composite material response in fires including the decomposition of the composite and the interaction with a fire. To adequately model composite material in a fire, two physical model development tasks are necessary; first, the decomposition model for the composite material and second, the interaction with a fire. A porous media approach for the decomposition model including a time dependent formulation with the effects of heat, mass, species, and momentum transfer of the porous solid and gas phase is being implemented in an engineering code, ARIA. ARIA is a Sandia National Laboratories multiphysics code including a range of capabilities such as incompressible Navier-Stokes equations, energy transport equations, species transport equations, non-Newtonian fluid rheology, linear elastic solid mechanics, and electro-statics. To simulate the fire, FUEGO, also a Sandia National Laboratories code, is coupled to ARIA. FUEGO represents the turbulent, buoyantly driven incompressible flow, heat transfer, mass transfer, and combustion. FUEGO and ARIA are uniquely able to solve this problem because they were designed using a common architecture (SIERRA) that enhances multiphysics coupling and both codes are capable of massively parallel calculations, enhancing performance. The decomposition reaction model is developed from small scale experimental data including thermogravimetric analysis (TGA) and Differential Scanning Calorimetry (DSC) in both nitrogen and air for a range of heating rates and from available data in the literature. The response of the composite material subject to a radiant heat flux boundary condition is examined to study the propagation of decomposition fronts of the epoxy and carbon fiber and their dependence on the ambient conditions such as oxygen concentration, surface flow velocity, and radiant heat flux. In addition to the computational effort, small scaled experimental efforts to attain adequate data used to validate model predictions is ongoing. The goal of this paper is to demonstrate the progress of the capability for a typical composite material and emphasize the path forward.

A thermal model is developed for the response of carbon-epoxy composite laminates in fire environments. The model is based on a porous media description that includes the effects of gas transport within the laminate along with swelling. Model comparisons are conducted against the data from Quintere et al. Simulations are conducted for both coupon level and intermediate scale one-sided heating tests. Comparisons of the heat release rate (HRR) as well as the final products (mass fractions, volume percentages, porosity, etc.) are conducted. Overall, the agreement between available the data and model is excellent considering the simplified approximations to account for flame heat flux. A sensitivity study using a newly developed swelling model shows the importance of accounting for laminate expansion for the prediction of burnout. Excellent agreement is observed between the model and data of the final product composition that includes porosity, mass fractions and volume expansion ratio.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Although smolder combustion has been extensively studied both computationally and experimentally, relatively few theoretical studies have examined the two-dimensional structure of the smolder wave. In this paper, two-dimensional smolder in polyurethane foam is modeled with a two-dimensional numerical formulation that includes a seven-step kinetic model of the polyurethane smolder reaction mechanism. The two-dimensional model formulation includes the effects of heat, mass, species, and momentum transfer of the porous solid and gas phase. The seven-step decomposition reaction mechanism, which includes a secondary char oxidation and an additional char pyrolysis step, was developed using genetic algorithm optimization. The mechanism is capable of modeling both forward and opposed smolder. The model was used to study the two-dimensionality of a forward propagating smolder wave. The model results show a two-dimensional structure in the temperature, species, and reaction profiles that agrees qualitatively with experimental observations. Oxygen is consumed at the reaction front, as expected, which leads to different reaction pathways governing the final products (i.e. thermal char and oxidative char). It was found that the model response is sensitive to boundary conditions, thermal properties, and heats of reaction for the char oxidation reaction. The incorporation of the secondary oxidation reaction step in the model paves the way to further analysis of the transition to flaming process. © 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.