publications
publications by categories in reversed chronological order. generated by jekyll-scholar.
2023
- MDSuite: Comprehensive Post-Processing Tool for Particle SimulationsSamuel Tovey , Fabian Zills , Francisco Torres-Herrador , and 3 more authorsJ Cheminform, Feb 2023
Particle-Based (PB) simulations, including Molecular Dynamics (MD), provide access to system observables that are not easily available experimentally. However, in most cases, PB data needs to be processed after a simulation to extract these observables. One of the main challenges in post-processing PB simulations is managing the large amounts of data typically generated without incurring memory or computational capacity limitations. In this work, we introduce the post-processing tool: MDSuite. This software, developed in Python, combines state-of-the-art computing technologies such as TensorFlow, with modern data management tools such as HDF5 and SQL for a fast, scalable, and accurate PB data processing engine. This package, built around the principles of FAIR data, provides a memory safe, parallelized, and GPU accelerated environment for the analysis of particle simulations. The software currently offers 17 calculators for the computation of properties including diffusion coefficients, thermal conductivity, viscosity, radial distribution functions, coordination numbers, and more. Further, the object-oriented framework allows for the rapid implementation of new calculators or file-readers for different simulation software. The Python front-end provides a familiar interface for many users in the scientific community and a mild learning curve for the inexperienced. Future developments will include the introduction of more analysis associated with ab-initio methods, colloidal/macroscopic particle methods, and extension to experimental data.
2022
- Study of the Degradation of Epoxy Resins Used in Spacecraft Components by Thermogravimetry and Fast PyrolysisFrancisco Torres-Herrador , Andreas Eschenbacher , Julien Blondeau , and 2 more authorsJournal of Analytical and Applied Pyrolysis, Jan 2022
Predicting the demisability upon re-entry of space debris objects is of great importance due to the threat these objects pose if they were to fall in an inhabited area. In particular, carbon/epoxy composite materials have been found on Earth in several occasions. Accurate models to assess the demisability of such components require, in particular, detailed thermal degradation data for the epoxy resin. In this work, we analyze a resin used to manufacture such components, using thermogravimetric analysis (TGA), organic elemental analysis, and pyrolysis coupled to comprehensive two-dimensional gas chromatography. The epoxy resin rapidly decomposed in a relatively narrow range of temperatures (300–400∘C) in more than 70 different volatile products. A one-step kinetic model is proposed for the pyrolysis of epoxy based on thermogravimetry observations. The information on the species and elemental composition can be used to develop more accurate material degradation models for predicting the demisability upon re-entry of space debris.
- Thermal Conductivity Evolution of Carbon-Fiber Ablators Submitted to High TemperaturesAlessandro Turchi , Francisco Torres-Herrador , Bernd Helber , and 4 more authorsJ Thermophys Heat Trans, Jun 2022
Carbon-phenolic ablators are widely used as thermal protection materials for atmospheric entry capsules. The knowledge of their thermophysical properties is therefore of primary importance to correctly simulate their thermal response, eventually reducing design safety margins without the risk of compromising the integrity of the underlying vehicle structure and payload. In this work, we present the results of an experimental work that aimed to evaluate the effective thermal conductivity of the carbon-phenolic ablator ZURAM\textregistered in its charred state. The material thermal conductivity was obtained, up to 2790^∘C, using the available heat-capacity law for this material, ad hoc laser flash analysis thermal diffusivity measurements, and material density estimates. The results suggest a strong impact of the material heating history on the thermal conductivity. As a consequence of this hysteresis-like behavior, measurements taken during the heating or the cooling phases differ sensibly, with discrepancies far beyond the quantified experimental uncertainties. Heating-phase measurements follow a specific trend and could be reduced to a fitting polynomial law with associated error bounds. Measurements performed during the cooling phase seem to be affected by a modification process of the material intrinsic properties that is speculated to be related to the graphitization of the carbon fibers composing the material.
2021
- Analytical Solution for Multi-Component Pyrolysis Simulations of Thermal Protection MaterialsJoffrey Coheur , Francisco Torres-Herrador , Philippe Chatelain , and 3 more authorsJournal of Materials Science, Apr 2021
This paper provides the analytical solution to a one-parameter Šesták–Berggren kinetic model for the thermoanalytical study of pyrolysis reactions involving multiple independent parallel reactions. Such multiple independent parallel reactions are widely used, for instance, in the modeling of the pyrolysis of thermal protection materials used in heatshields for spacecraft during the atmospheric entry phase. Solving inverse problems to infer parameters of the kinetic model through optimization techniques or Bayesian inference methods for uncertainty quantification may require a large number of evaluations of the response and its sensitivities (derivatives with respect to parameters). Moreover, in the case of kinetic equations, the Arrhenius parameters can exhibit strong dependence that can require further model evaluations for an accurate parameter calibration. The interest of this analytical solution is to reduce computation cost while having high accuracy to perform parameter calibration from experiments and sensitivity analysis. We propose to use exponential–integral functions to express the solution of the temperature integral, and we derive the analytical solution and its sensitivities for the parallel reaction model both for constant temperature (isothermal) and for constant heating rate conditions. The solution is validated on a six-equation model using parameters inferred in a previous work from the experimental data of the pyrolysis of a phenolic-impregnated carbon ablator material, and we compare the computational cost and accuracy of the implemented analytical solution with a numerical solution. Our results show that the use of such analytical solution with an accurate computation of the exponential–integral function significantly reduces the computational cost compared to the numerical solution.
- Decomposition of Carbon/Phenolic Composites for Aerospace Heatshields: Detailed Speciation of Phenolic Resin Pyrolysis ProductsFrancisco Torres-Herrador , Andreas Eschenbacher , Joffrey Coheur , and 3 more authorsAerospace Science and Technology, Dec 2021
Thermal Protection Materials (TPM) such as carbon/phenolic composites are used to protect spacecraft structures from extreme conditions. This protection is, in part, achieved by the decomposition via pyrolysis of the phenolic resin. Finite rate chemistry models are however still unable to predict the chemical production rates and composition of the pyrolysis products accurately. This is mostly due to the scarcity of experimental data for model validation. In this work, the decomposition of a phenolic material representative of thermal protection material is studied in a unique micro-pyrolysis unit for the temperature range 300-800^∘C. This unit is equipped with highly sensitive detectors allowing us to identify and quantify products in a broad range of molecular weights up to 240 gmol-1. More than 50 different products of the pyrolysis of phenolic resin have been quantified with a mass balance closure greater than 80%. The major compound groups found are permanent gases, phenols as well as larger molecules such as diphenols and naphthalenes. In addition, the char yield obtained at the fast heating rates employed in our apparatus was found ∼5%-points lower compared to traditional thermogravimetry.
- Determination of Heat Capacity of Carbon Composites with Application to Carbon/Phenolic Ablators up to High TemperaturesFrancisco Torres-Herrador , Alessandro Turchi , Kevin M. Van Geem , and 2 more authorsAerospace Science and Technology, Jan 2021
Simulations of atmospheric entry of spacecraft and satellites require accurate knowledge of thermo-physical properties such as heat capacity in a wide temperature range. However, the characterization of this quantity is not straightforward for carbon composites at high temperatures, due to pyrolysis reactions that occur in the material. We develop a methodology for determining the heat capacity and required heat of pyrolysis for carbon composites in these conditions. The methodology consists of three steps: organic elemental analysis to determine composition, differential scanning calorimetry experiments on the different components to determine apparent heat capacity, and computations to separate the apparent heat capacity into heat capacity and heat of pyrolysis. This methodology is applied to the Zuram\textregistered carbon/phenolic ablator from room temperature up to 1100 K. The results obtained were compared to separate analyzes of the different components of the material, assuming that heat capacity is an additive property. It was found that compressing the samples into disks provides improved resolution and repeatability for low density materials. This provided a determination of the heat capacity of the decomposing composite with a relative standard deviation <10% and of <20% for the heat of pyrolysis. The proposed methodology can directly be applied to other carbon composites such as carbon/epoxy systems.
2020
- Competitive Kinetic Model for the Pyrolysis of the Phenolic Impregnated Carbon AblatorFrancisco Torres-Herrador , Joffrey Coheur , Francesco Panerai , and 4 more authorsAerospace Science and Technology, May 2020
Carbon/phenolic ablators are successfully used as thermal protection material for spacecraft. Nevertheless, their complex thermal degradation is not yet fully understood, and current pyrolysis models do not reproduce important features of available experimental results. Accurate and robust thermal degradation models are required to optimize design margin policy. We investigate whether the competitive kinetic schemes commonly used to model biomass pyrolysis are appropriate to describe the thermal degradation of carbon/phenolic composites. In this paper, we apply competitive pyrolysis mechanisms for the thermal degradation of the carbon/phenolic ablator PICA. Model parameters are then calibrated using a robust two-step methodology: first deterministic optimization is used to obtain the best estimation of the calibration parameters based on the experimental data, then a stochastic Bayesian inference is performed to explore plausible set of solutions taking into account the experimental uncertainties. The proposed calibrated model provides an accurate description of the pyrolysis process at different heating rates. The model shows great flexibility and robustness at a similar computational cost as the traditional devolatilization models. This opens the possibility for more complex mechanisms when more experimental data becomes available.
- Multicomponent Pyrolysis Model for Thermogravimetric Analysis of Phenolic Ablators and Lignocellulosic BiomassF. Torres-Herrador , V. Leroy , B. Helber , and 3 more authorsAIAA Journal, May 2020
A multicomponent kinetic mechanism has been developed for the pyrolysis at low heating rate of carbon/phenolic thermal protection material and a wood species. An experimental campaign has been carried out using thermogravimetric analysis to study the mass loss under different conditions of crucible (with or without a lid) and heating rate for both materials. Using a pierced lid to cover the crucible during pyrolysis promotes char production compared with the case of open crucible. Kinetic parameters were then extracted from the experiments by an optimization approach using an in-house-developed kinetic identification code. The parameters recovered for the two applications allow to reproduce accurately the mass loss evolution.
2019
- A High Heating Rate Pyrolysis Model for the Phenolic Impregnated Carbon Ablator (PICA) Based on Mass Spectroscopy ExperimentsFrancisco Torres-Herrador , Jeremie B. E. Meurisse , Francesco Panerai , and 5 more authorsJournal of Analytical and Applied Pyrolysis, Aug 2019
A novel model for the pyrolysis of the Phenolic Impregnated Carbon Ablator (PICA) at high heating rate is developed and calibrated based on high fidelity thermal decomposition experiments. The calibration relies on accurate quantification of pyrolysis gases obtained from mass spectroscopy analysis during thermal decomposition at fast heating rates simulating flight conditions. Model calibration is achieved by coupling the Porous material Analysis Toolbox based on OpenFOAM (PATO) with an optimization software (Dakota). A multi-objective genetic algorithm is used to fit the experimental data by optimizing the model parameters for an element and a species-based formulation. The new model captures both the material mass loss and the gaseous species produced during pyrolysis.