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Computational Methods for Thermal Properties of Composites

#0804


Development of Experimental and Computational Methodology for Investigation of thermal Properties of Composite Materials Based on Inverse Problem Theory and Stochastic Approaches

Tech Area / Field

  • MAT-COM/Composites/Materials

Status
8 Project completed

Registration date
21.11.1996

Completion date
07.09.2000

Senior Project Manager
Komashko B A

Leading Institute
MAI (Moscow Aircraft Institute), Russia, Moscow

Collaborators

  • University of Leeds, UK, Leeds\nISITEM, France, Nantes\nEuropean Space Agency / European Space and Technology Center, The Netherlands, Noordwijk

Project summary

The reliable thermal protection and insulation design problem becomes very important for structures under design weight limitations (space vehicles, aeronautical engineering, etc.). It is impossible to create reliable thermal protection and insulation system without carrying out of certain theoretical and experimental investigations of materials properties. Design of modem machines and energy production equipment is based on the mathematical models of corresponding physical processes. Widely using composite materials, ceramics and others' materials work under extreme thermal conditions with high temperatures and thermal loads. Under such conditions the methods of traditional metrology cannot give satisfactory values of their different properties, in particular, their thermophysical characteristics. It leads to difficulties in the design of systems and control of thermal processes because of high uncertainties in the above mentioned models.

In many practical situations it is impossible to measure directly such properties of analyzed materials (for example, composite) as thermophysical characteristics. The only way, which can often be used to overcome these difficulties, is indirect measurements. This type of measurements is usually formulated as the solution of inverse heat transfer problems. Such problems are ill posed in mathematical sense and their main feature shows itself in the solution instabilities that are why special regularizing methods are needed to solve them. The experimental methods of identification of the mathematical models of heat transfer based on solving of the inverse problems are one of the modem effective solving manners. Another direction of research is the development of theoretical models based on stochastic analysis of properties and structure of materials.

In the Former Soviet Union, a wide activity has been, done in this field by the scientific institutions connected with defense and aerospace industries. The goal of this project is to preserved the high level of investigations earned out by the scientific teams and to assist the conversion to civilian use, by supporting financially these teams. Such research institution as 1SITFM (France) are interested in obtaining information of main results in this field and in transferring them to manufacturing industries as car industry, composite material production, casting and others.

The approach based on inverse methods has been analyzed separately in different countries and appears to be effective in the analysis of heat transfer processes in manufacturing of modem high temperature composite materials, car industry, aerospace industry, metallurgy, thermal control system and others. New metrology under development is the combination of accurate measurements of thermal quantities which can be experimentally observable under working conditions and accurate data processing which are based on the solutions of inverse heat transfer problems.

In the project, the development of methods for estimating thermophysical characteristics is carried out for thermally stable high temperature» composite materials. For such materials the goal is to estimate the characteristics as temperature functions by using results of measuring boundary conditions and temperature histories inside the body consideration. For estimating thermophysical characteristics, it is extremely important to provide the maximum accuracy of final results. The way of improving the accuracy is based on the concepts of experiment design. This problem is also under analysis in the project. The experiment design problem is to choose such experimental conditions including heating rates and temperature measurements under which the accuracy will be maximized. One of the goals of the project is to develop methods and numerical algorithms for solving experiment design problems.

Another important direction of research is connected with development of theoretical mathematical heat transfer model for modern materials. Approach to the solving of the problem will be based on estimates of the stochastic characteristics of their elements (fiberglass, etc.). This approach will be based on the research of highporous fibrous thermal protection materials and can be used for investigation of composite materials based on fibers SiC, AlO, MgO, ZiO. 1SITRM also will can take, take in experimental part of proposed project in the field of analysis of microstructure of materials, distribution of particles by size and type of orientation, diameter of contact /ones, etc. and identification of physical properties of fibers: conductivity, heat capacity, density, complexive refraction index as function of wavelength etc. After the theoretical and experimental research of thermal processes in materials under consideration, results of these two approaches will he compared and theoretical model of heat transfer can he improved based on inverse problems method.

Solution of this problem is widely utilized for development of new composite materials working under intensive heat load conditions. Creation of such materials is closely connected with the possibility to predict their properties and development the methods allowing making an express analysis of influence of composite materials structure on its properties. The field of project is interdisciplinary and needs to be brought together new results obtained in '1 hermophysics. Thermal Measurements, Applied Mathematics, Computer Science, Experiment Design and Data Processing.

Results of the project will include numerical algorithms for experimental data processing to estimate thermophysical properties of materials, theoretical approach for creating stochastic mathematical models of heat transfer at composite materials and recommendations for their practical applications. Project implementation will provide development of the method for estimation and prediction of the properties of materials for complex structure, taking into consideration a stochastic, spread of properties of material components depending on temperature, pressure, wavelength etc.

The methodology of investigations being developed will permit


- on a common theoretical base to solve a set of problems emerging in designing and developing heat-loaded systems, structures and materials;
- to consider to the maximum the actually existing nonstationarity, nonlinearity and multidimensionality of heat-and-mass transfer processes running in materials and on the surface of structures, this sufficiently increasing the accuracy and truth of the results of the results of investigations;
- to increase the information efficiency of experiments and tests, provide a possibility to conduct them in the conditions approximate to the maximum to full-scale conditions;
- to predict and specify with high accuracy the properties of new materials over a wide range of temperature change, pressures and heating rates, this accelerating introduction of perspective materials;
- to reduce largely the volume of necessary experimental investigations and tests, and, consequently, the expenses in resources and time for the development of technology prototypes.


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