EVALUATION OF THE PRACTICALITY OF METHODS AND FORMS OF SAMPLES FOR THE DETERMINATION OF PHYSICO-MECHANICAL PROPERTIES OF WOOD
The deformed state of heterogeneous orthotropic samples modeling wood under compression and shear, one surface of which is supported by a plate of isotropic material, was investigated by the finite element method in the software product MSC Patran-Nastran. It is shown that the application of the method of photoelastic coatings to determine the elastic moduli of the spring and summer layers in investigating the crushing of wood in the direction across the fibers can lead to significant errors. Assessment of a relative error of definition of modules of elasticity of spring and summer layers is executed by method of photo elastic coatings. The relative mistake in determination of sizes of modules can reach 20 %. The analysis of tension of external surfaces of the most widespread samples on shearing from pine wood a finite element method has shown that in the neighborhood of the shearing plane for all studied samples uniform tension doesn't come. In the plane of shearing of the sample recommended by the standard of ASTM (D 5379-93), tension approaches uniform; for the standard sample recommended to State standart specification tension at the beginning and at the end of the plane of shearing differs from uniform; in the sample offered in the patent for an invention No. 2295717, tension it is non-uniform.