Viazovychenko Y. Thermo-stress state of viscoelastic rubber-cord elements of structures taking into account energy dissipation during cyclic deformation

Thesis is presented for Scientific Degree Candidate of Technical Sciences, speciality 05.02.09 – Dynamics and Strength of Machines. – National Technical University, «Kharkiv Polytechnic Institute», Kharkiv, 2021. The thesis deals with a solution to the applied problem of the development of computational approaches to study the peculiarities of thermal and deformation processes that accompany the work of viscoelastic materials in mechanical engineering elements with reinforced rubber composites. The object of research is the processes of formation of the thermo-stress state in rubber-cord elements of mechanical engineering elements operating in the conditions of cyclic deformation taking into account energy dissipation. The main theoretical statements of the dissertation are formulated in the framework of the fundamental of the theories of elasticity and viscoelasticity, thermal conductivity and thermoelasticity. The assessment of cycling deformed and stressed states have been carried out within the framework of 3d computer modelling tools using the finite element method (FEM). A multi-layer structure of composite elements is modelled explicitly. A unified methodological approach is proposed to the computational modelling of thermo-stress state, which is caused and accompanied by heat accumulation due to energy dissipation during cyclic deformation of viscoelastic rubber-cord elements of mechanical engineering structures. The approach allows to determine inhomogeneous temperature field distribution in structural elements caused by operational load cycles, as well as the impact of these thermal processes on the stressed and deformed states of structures. A set of experimental tests on cyclic deformation of the unidirectional textile reinforced rubbery composites have been done. Viscoelastic characteristics of this material and the heat generation indicators required for the application of the computational approach in applications have been experimentally found. Significant amplitude dependence of the storage modulus and relaxation time is observed during cyclic deformation of the material under study. A level of temperature rate and value of self-heating depending on the frequency and amplitude of cyclic deformation of the materials is determined. A specific procedure and software for the identification of the viscoelastic and dissipative material parameters based on computational modelling of the temperature state of cyclically deformed specimens and experimental observations are developed. The procedure is seeking the material parameters through the minimization of the error of the difference of simulated and experimentally observed self-heating temperature by the method of stochastic optimization. The application of this approach allowed to identify the viscosity parameters material parameters. Based on the results, a critical comparison of an volume of energy released in hysteresis loops that theoretically calculated from the model with identified from self-heating temperature data under different load conditions to independent experimental measurements showed their satisfactory convergence and justified the main methodological hypothesis of the current work. The applied engineering problem of calculation of the thermo-deformed state of a pneumatic tire on the basis of the developed in the research computational approach and found experimental data are solved. A number of three-dimensional FE models of pneumatic tires has been created, which allow to determine its thermal and stressed states that formed in operation. The models have been created in 3d statement considering multilayer structure, curvilinear orthotropic properties, geometric and physical nonlinearity within the submodeling approach. A deformed state of pneumatic tires has been carried out depends on the different load cond itions as well as on the temperature field that is generated. The influence of the thermal field on the deformed state of a pneumatic tire is investigated. The results obtained in the dissertation are implemented in the practice of designing, research and development work of JSC "ROSAVA TIRERS" (tire engineering and manufacturing company), and into the educational process of NTU "KhPI".