The relevance of studying the mechanical properties of reinforced composite materials and developing methods and techniques for describing the mechanical behavior and strength of structural elements and machines made of them is determined by the lack of knowledge of some phenomena that are manifested by composite materials and affect their mechanical behavior, limitations of mathematical models available for its description, as well as a positive economic and practical effect from an optimal use of composite materials in the domestic industry.
The aim of the study is a theoretical and experimental evaluation of anisotropy of viscoelastic properties of polymer reinforced composite materials, the degree of which does not depend on the degree of anisotropy of elastic properties, as well as a development of a calculation method for a consideration of the general degree of anisotropy of viscoelasticity for analyzing structural strength of elements of structures and machines subjected to static and thermomechanical loading.
The object of the study is phenomena of anisotropic elasticity and viscoelasticity of polymer reinforced composite materials, as well as the contact mechanical behavior of elements of structures and machines made of them.
The subject of the study is mechanical properties of polymer reinforced composite materials that require adequate identification of anisotropic viscoelasticity parameters as well as mathematical models that can accurately describe their mechanical behavior.
The theoretical positions of the dissertation work are based on methods of engineering and structural mechanics, namely, the methods of the viscoelasticity theory, the finite element method, the least squares method, the method for solving systems of differential and integral equations.
The scientific novelty of the obtained results consists in the following done for the first time:
– for the first time a method that does not require the writing of additional modules or procedures for computer-aided engineering programs was developed, which allowed to simulate the general degree of anisotropy of viscoelastic properties of a material in these programs. The satisfactory convergence of this method and its applicability to a solution of applied scientific and engineering problems was proved;
– for the first time, with the help of the created numerical methods of homogenization and experimental study of orthotropic viscoelastic properties of polymer reinforced composite materials at elevated temperatures, a disproportionality of composite viscoelastic properties with its elastic properties and an unavailability of the relaxation curves of the technical parameters of viscoelasticity were proved, which justifies a necessity of taking into account the effect of anisotropic viscoelasticity. In addition, it has been established that the temperature shift function of the composite qualitatively and quantitatively coincides with the matrix shift function;
– for the first time, analytical and numerical-analytic models of the planar axisymmetric contact behavior of the elastic pipeline with viscoelastic bandage were built, allowing for taking into account the different modes of a mounting of the bandage and a degree of anisotropy of the viscoelastic properties.
The practical significance of the obtained results for machine building is that the integrated approach to numerical and experimental identification of anisotropic viscoelasticity parameters of polymer reinforced composite materials presented in the work, as well as the method of their modeling in computer-aided engineering programs are a closed scheme for an account of such a phenomenon at calculations of the strength of composite elements of structures and machines. This was realized in a determination of the stress-strain state of the pipeline with an orthotropic viscoelastic band. The developed analytical and numerical-analytical models of their contact enable quick simulation of the repair process and determination of a repair efficiency with high accuracy, which can be used in a practice of repair works of domestic main pipelines.
Relationship of work with scientific programs, plans, themes. The dissertation was performed at the Department of Dynamics and Strength of Machines of the National Technical University "Kharkiv Polytechnic Institute" (NTU "KhPI") basing on the plans of research work in accordance with the tasks of the International Research Project "Innovative Non-Destructive Testing and Advanced Composite Repair of Pipelines with Volumetric Surface Defects (INNOPIPES), held from 2012-2016 under the 7th EU Framework Program, Action by Maria Curie (Contr. No. PIRSES-GA-2012-318874); Scientific Research Work of the Ministry of Education and Science of Ukraine "Development of methods for mathematical modeling of the behavior of new and composite materials for resource estimation and prediction of the reliability of structural elements" (DR No. 0117U004969).
