| Abstract [eng] |
In this work researches in order to determine, how the drying defects affect the mechanical properties of wood, were performed. 60 birch wood samples of different thickness (thin (P), medium thickness (V) and thick (S)) were used for analysis. Wood mechanical properties were evaluated using transverse resonant vibration method. Resonant frequency and amplitude of wood specimens was measured to calculate modulus of elasticity (E) and damping coefficient (tgδ) of wood. The analysis of the results showed how the defects have changed wood elastic and viscosity parameters. It was found that first mode of vibrating wood samples at first resonant frequency complied with first theoretical beam mode. It was determined that resonant frequency decreased by 30-110 Hz, because of the formed cut. Mode and amplitude-frequency characteristic of the samples also changed because of that. Modulus of elasticity decreased and damping coefficient increased because of the defect in wood samples. It was obtained that when modelling wood cracks in the samples their mode and amplitude-frequency characteristic changes are analogous to the specimens with drying defects. Due to different cracks in samples, resonant frequency decreased by 5-43 Hz, modulus of elasticity decreased by 440-3040 MPa and damping coefficient increased by 0,004-0,015. The statistical analysis showed the increase of mechanical parameters dispersion, caused by different drying defects in wood samples. |
