ИССЛЕДОВАНИЕ АНИЗОТРОПИИ ДРЕВЕСИНЫ ПРИ ДИНАМИЧЕСКОМ НАГРУЖЕНИИ

Abstract

Wood is widely used as a shock absorbing material in various special layered protective structures, for example in containers for the transportation of hazardous materials and substances including: nuclear waste, defense components, a wide range of toxic substances, etc. For the design of such structures and for modelling their behaviour under dynamic load conditions, models equipped with authentic parameters are required. Since wood is a highly anisotropic material, this effect should be taken into account in numerical simulation using the mathematical relationships of an orthotropic solid. Under conditions of a uniaxial stress state, the behaviour of the three structural wood species is studied: pine, birch and sequoia. To achieve a greater degree of deformation the mode of multicyclic loading of the specimen was used. The stress-strain curves of pine and birch were obtained when the specimens were loaded along and across the fibers. Strength and deformation behavior (including the maximum flow stress) characteristics of the tested wood species were determined. It is shown that the yield strength of the three species of wood along the fibers is almost ten times higher than the strength across the fibers. The ultimate strength across the fibers is significantly higher than along the fibers. The energy absorption of pine and birch was determined to facilitate a comparative evaluation of their damping abilities. It is noted that birch exhibits greater energy absorption than pine both along and across the fiber directions.Analysis of the effect of the stress state on the strength and deformation properties was also carried out for sequoia. Specimens sectioned as a function of direction and their subsequent loading response were carried out at angles of 0°, 30° and 90° relative to the fiber direction. Under uniaxial loading conditions, the non-uniformity of the radial expansion of the specimens with different directions relative to the wood grain orientation was evaluated. It was found that lateral confinement strongly affects the stress-strain behavior of the sequoia wood species suppressing cracking along the fibers and thereby suppressing damage evolution and final fracture.