THE RHEOLOGICAL MODEL OF LIMITED CREEP OF WOOD

Abstract

Rheological properties of wood and deformation features depending on different conditions of temperature, humidity, and mechanical stress are used to improve existing and develop new technologies of hydrothermal and mechanical treatment. The solution of this task is complicated as wood belongs to the class of physically nonlinear, natural heterogeneous polymers, characterized by high hydrophilic and a wide range of physical and mechanical characteristics. Therefore, the research of rheological behaviour of wood depending on directions of anisotropy, determination of the characteristics of creep or relaxation functions is an actual task. In the course of study the authors have defined the function of creep and have also got dependences of time relaxation of wood. Firstly, studies of the rheological behaviour of wood concerning the structural anisotropy under conditions of limited creep are presented. Then the authors have obtained the rheological model of high-elastic deformation with stress. The built algorithms of determination of descriptions of rheological conduct of pine and fir wood are based on approximation of experimental information. Moreover, the ratio between instantaneous and protracted modulus of elasticity for pine and fir wood in tangential direction of the deformation was determined. Regularities of creep deformation of wood were investigated. For the approximation of experimental curves of creep we used the method of interpolation function as a sum of exponentials. To define the analytical form of the kernel of creep required to calculate the strain-relaxation properties of wood we used experimental data of creep deformation of the material. Thus, the choice of a creep kernel is determined by the features of rheological behaviour of wood. The authors have presented comparison of theoretical researches to the approximated experimental curves of high-elasticity deformation of pine and fir wood in the case of determination of rheological descriptions in the conditions of aftereffect.