Kryshtapovych V. Regularities of influence of non-isothermal moisture transfer on structural and mechanical properties of wood.

The object of study - deformability of wood in conditions of non-isothermal moisture transfer (on the example of pine and fir). The purpose is determination of rheological behavior and prediction of the regularities of deformation-relaxation processes of wood in conditions of changing temperature and humidity. The methods - methods of the mechanics of hereditary media for the construction of mathematical models; experimental static methods for determining the rheological properties of wood; the method of numerical integration, approximation methods and methods of mathematical statistics for the processing of experimental data using software and algorithmic means; methods of physical analogies for forecasting deformability of wood. Scientific novelty. A new mathematical model for determining the visco-elastic state of wood with variable moisture content is constructed, which, unlike the others, takes into account elastic and viscoelastic deformations and deformations due to drying and the mechanism of creep sorption. For the first time, the functions of the rheological behavior of wood depending on the directions of structural anisotropy in conditions of temperature and humidity change, which allow within the model to quantitatively describe and predict the processes of creep and relaxation of wood, taking into account the mechanism of degeneration of deformations, are determined. The method of physical analogies for forecasting the creep of wood along the fibers in conditions of temperature and humidity changes, which allows, based on the results of short-term studies, to predict the rheological properties of limited creep for a long time. The algorithms are constructed and new regularities of the change of the functions of time temperature-humidity shift are established. It is established that the influence of temperature-humid conditions is taken into account by variable parameters of models, which allows quantitatively to express the laws of viscoelastic deformation of wood depending on the specific modes of interaction. This enables to predict deformation-relaxation properties of wood and to calculate the time dependences of deformation and relaxation of stresses on the basis of certain models without carrying out appropriate experimental studies in a wide range of changes in temperature humidity. Practical meaning. The developed algorithms and software will allow, based on the experimental data of the creep curves, to determine the parameters of the rheological behavior of wood in the direction of anisotropy, depending on the temperature and humidity changes. The established functions of time shift and obtained calculation dependences of the definition of components of wood deformation, relaxation times can be used to predict the rheological properties of wood under different conditions of change in temperature and humidity, in particular, to determine the deformability of wood compounds during surface treatment. The results of the dissertation work were used on the "Leda S-Ukraine" (Khust, Zakarpattia region) for determining the mechanical characteristics and stress-strain state of the wood in the process of drying, which enables to justify the choice of technological parameters to ensure the required quality of products (according to the act of June 20, 2017). The results of scientific research have been used and reflected in the programs of the disciplines of the Department of Automation and Computer-Integrated Technologies of the National Forestry University of Ukraine: "Identification and modelling of technological processes", "Quality control and methods of non-destructive control" for the preparation of bachelors and masters (according to the act dated 19.07 .2017 р.). The sphere of use: technology of wood processing and manufacture of wood products.