The dissertation is devoted to the development of algorithm and also scientific and technical bases of system improvement of strength and deformable properties of solid wood (deciduous and coniferous species) and composite materials based on it with predicted characteristics for design, repair, reconstruction, maintenance and manufacture of structural parts, materials, products, elements , structures used in various sectors of the economy (construction, woodworking, mining, river and sea, fuel and energy complex, mechanical engineering, shipbuilding, bridge structures and many others).
The first section is devoted to an overview of the stages and current state of experimental and theoretical research and existing methods of testing solid, glued and modified wood.
The second section describes the method and equipment used in conducting experimental studies of the main strength and deformable properties of solid wood and composite materials based on it with a single axial compressive longitudinal short-term load. Selected materials and parameters are specified in the manufacture of basic and auxiliary prototypes. The polymer composition "silor" was chosen for surface and deep modification of prisms from solid and glued wood. It is offered for the analytical description of diagrams of deformation of continuous wood and its composites on the basis at all stages of work by the polynomial of the 4th degree which gives good convergence of experimental and theoretical values, both on ascending, and on descending sites of real and optimized diagrams. Working hypotheses and prerequisites for modeling the stress-strain state of the normal cross section of solid and modified wood elements are proposed. For the first time, a formula for determining the critical deformations of the investigated materials, which includes elastic and plastic components was proposed, and developed a calculation apparatus for determining the ultimate relative deformations based on the diagram "moment-curvature" of the bending element of rectangular cross section.
The third section is devoted to the description of the obtained results of experimental-theoretical researches of diagrams of mechanical condition of 60-year-old coniferous and deciduous wood and influence of moisture on strength and deformable properties under axial compression along fibers by one-time short-term loading. The main areas and parameters of the mechanical state of wood under compression, as well as critical and ultimate relative deformations at a humidity of 12%, 21% and 30% are determined. A generalized analytical description of the mechanical state of solid wood of different breeds and humidity under a single short-term longitudinal deformation in the rigid mode of operation from the beginning of work of prisms to the destruction is proposed. It is established that the process of drying wood (from 30 to 12%) improves its basic strength and deformable properties, in particular increases the strength by 1.85 –2.33 times, the initial modulus of elasticity by 1.18–1.61 times and reduces the deformability.
The fourth section covers the issues of experimental-theoretical studies of the influence of age on the diagrams of mechanical state and strength, as well as deformable properties of deciduous and coniferous species under single loads of axial compression along the fibers of working prisms in the rigid mode. It is established that the main strength and deformability parameters of the deformation diagram slightly decrease from 60 to 40 years and significantly from 40 to 20 years: the strength of wood in the range from 60 to 20 years by 27–45%; initial modulus of elasticity by 12–17%; critical relative deformations of deciduous and coniferous species by 19–49%; limit deformations by 8–39%.
The fifth section is devoted to the study of solid and glued wood of different species, which were modified with a polymer composition "silor" under natural surface and forced deep impregnation. It is established that the tensile strength of samples of glued wood of coniferous and deciduous species increases by 13–25%, and the deformability in one direction or another insignificantly increases or decreases. Deformability decreases in the range of 14-35%. The initial modulus of elasticity of the studied samples is greater by 23–55%. It was found that the strength of deeply modified materials by the polymer composition "Silor" increases in the range of 17–21%, deformability (critical relative deformation) is reduced by 7–20%, and the initial modulus of elasticity increases significantly by 26–35% compared with wood of the same breeds modified superficially.
The sixth section describes the scope of valid (complete) and optimized (with a limit at the point of boundary deformation) diagrams of "stress - strain". Using such diagrams, the mathematical apparatus of calculation of various elements and constructions on the basis of continuous, glued and modified wood is improved.
