Flud L. Substantiation criterion strength of wood during drying process as anisotropic material

Object of research - strength of wood. The purpose is to substantiate the criterion of short-term wood strength for determining the boundary stresses and the permissible variation of moisture in the dried lumber. Methods - methods of solid state mechanics and theory of heat transfer; the Ritz method for determining the permissible variations of moisture and boundary stresses in lumber with a plane stressed state in the tangential-radial plane of structural symmetry; experimental static methods for determining the strength limits of anisotropic materials in directions of structural symmetry; interpolation and statistical methods for the processing of experimental measurements results; optical and conductometric methods for controlling the current humidity of the layer and the central layer in the dried lumber.Academic novelty.For the first time it was discovered that the plane boundary stress state in the tangent-radial plane of structural symmetry of hardwood is succesfully described by Ashkenazi O.K., and softwood species - the Goldenblat-Kopnov criterion; a new mathematical model for the determination of marginal stress fields in tangent lumber from coniferous and hardwood species was developed; for the first time it was established that in the formation of lumber with unevenly distributed moisture fields, the boundary stress state is a monovalent stressed state of tensile strength, and in the central layer it is a biaxial stressed state; new formulas have been derived for determining tolerable moisture variations in tangent lumber with parabolic and cosine distribution of moisture fields by their thickness. Practical importance. A new method of non-destructive control of the difference between permissible and actual moisture variations in lumber with variable non-uniformly distributed moisture fields is proposed, which makes it possible to detect in a timely manner hazardous quality of the field of stress in wood. The results of dissertation work, that is proposed method of non-destructive control of the difference between permissible and actual moisture drop in the process of drying of sawn softwood species, was introduced in LLC "Oskar-parket" Lviv. Branch of usage: woodworking technology and wood products manufacturing.