The effect of orthotropic wood properties on the stress field and the formation and growth of cracks during drying

Les je naravno gradivo, ki se zaradi večje okoljske ozaveščenosti čedalje pogosteje uporablja v inženirskih konstrukcijah. Težava uporabe lesa pa je, da začne ob izpostavljenosti vremenskim vplivom postopoma degradirati, kar se izrazi npr. v razpokanosti. Ker lahko razpoke, zlasti na nosilnih elementih večjih dimenzij, oslabijo njihovo trdnost in kvarijo videz, se jim poskušamo izogniti, za kar pa je potrebno dobro poznavanje mehanike procesov v lesu pri sušenju. V delu so obravnavani vplivi krčenja lesa zaradi procesa sušenja na napetostno polje, ki se pri tem pojavi. Izpostavljen je predvsem vpliv polarne ortotropnosti, ki je posledica rasti dreves. Postavljen matematični model, ki temelji na metodi končnih elementov, upošteva spreminjanje porazdelitve vlažnosti po prerezu v času in nastanek napetosti zaradi posledičnega krčenja. Pri tem je uporabljen konvekcijski robni pogoj sušenja. Algoritem je zmožen napovedati mesta največjih vrednosti nateznih napetosti in širjenje razpok v okroglem in kvadratnem preseku lesenega elementa.Wood is a natural material that is being increasingly used in engineering structures due to greater environmental awareness. The problem with using wood, however, is that it begins to gradually degrade when exposed to the weather, which can express e.g. in cracking. Since cracks, especially on the supporting elements of larger dimensions, can weaken their strength and affect their appearance, we try to avoid them which requires a good knowledge of the mechanics of wood drying processes. The study deals with the effects of wood shrinkage due to the drying process on the stress field that is induced during this process. The effect of polar orthotropy, which is the result of tree growth, is highlighted. A mathematical model based on the finite element method takes into account the change of moisture distribution across the cross-section over time and the formation of stress due to the resulting shrinkage. A convection drying boundary condition is used. The algorithm is capable of predicting the locations of maximum values of tensile stresses and the propagation of cracks in the round and square cross-section of a wooden element