Equation of state for polytetrafluoroethylene (PTFE) and mixtures with PTFE.

摘要

In this work, the goals are to explore the potential of different structural energetic materials that are made from different combinations of reactive materials, different binders and voids. In such exploratory studies, it is necessary to consider different ratios of the basic ingredients. Because the dual functional energetic structural materials are used in applications where the resulting structure encounters high intensity impact loads, impact and penetration into selected targets and shock induced chemical reactions, it is also necessary to consider large or finite deformations of these materials. The experimental techniques that are used consist of techniques such as the gas gun tests and flyer plate impact tests. To accomplish the exploratory tasks that are stated in the last few sentences requires a very large number of tests. Thus it is both expensive and time intensive.;Thus, it is necessary to consider alternate methods of determining the constitutive equations without conducting tests. This is accomplished by the use of ab initio methods to obtain the constitutive relations and foundations for chemical reactions in structural energetic materials without conducting tests. This needs an exploration of the analysis beyond continuum. First, it is necessary to study the quantum many body problem to quantitatively determine the internal energy of the material when subjected to different strain conditions. The current state of the technology is such that it is not possible to obtain an exact solution to the needed quantum many body problem that is modeled by the Schrodinger's equations. It is possible to solve these equations approximately by the approximation of density functional theory and Kohn Sham approximate equations. This however, yields only energies at the ground state or at absolute 0°K. Thus it becomes necessary to add both the lattice thermal contributions due to phonons and electron thermal contribution. Then, resulting energy is used to bridge to the continuum level and obtain the constitutive equations. This is the procedure that is used in this work.;Specific objectives of this study are not to design such materials but to characterize these materials. The primary research issues are the determinations of the constitutive relations for finite deformation of these energetic structural materials that can be designed to withstand impact loads. The issues of the constitutive equations form the focus of this thesis.;More specifically, the scope of the thesis is further reduced to analyze the constitutive equations of specific mixtures of nickel, aluminum with PTFE or Teflon as the binder. The equations of state p=P(rho,T) of the individual elements (nickel and aluminum), from ab initio studies, are reported in the literature. It is to be noted that the equations of state forms only a part of the complete constitutive relationships. However, the equation of state of PTFE, the equations of state of the mixtures of nickel, aluminum and PTFE are not studied or reported in the literature. Similarly, the problem of determination of the complete constitutive equations of crystalline materials, from ab initio methods under conditions of finite deformations, is still an open research area. The published papers do not consider the satisfaction of the principle of objectivity, the material symmetry conditions and the polyconvexity of the resulting expressions for the strain energy. Thus this thesis presents solutions to the following problems. (1) Determination of the thermodynamically complete equation of state of the binder and the energetic material PTFE or Teflon, from ab initio methods based on the density functional theory and Kohn Sham equations. (2) Determination of the equations of state of the granular composite or the mixture of nickel, aluminum and PTFE from ab initio methods. (3) Determination of the complete constitutive equation of aluminum, from ab initio methods, under conditions of finite deformations, with principle of objectivity, material symmetry conditions and polyconvexity of the strain energy.;All results are compared to test results whenever they are available. (Abstract shortened by UMI.)