WOOD RESEARCH Volume 63, Number 2, 2018
Sara Essert, Vera Rede, and Zrinka Švagelj

The bending modulus of elasticity of subfossil elm wood

The paper presents the results of the research of the bending modulus of elasticity of some 700 year old subfossil elm wood (Ulmus minor) retrieved from the Sava riverbed (Bosnia and Herzegovina). The subfossil elm wood is very rare to find and is highly appreciated in this form for its beautiful appearance and specific mechanical properties. Adult elm trees are nowadays also very scarce in natural forest stands of SE Europe, due to the invasion of the Dutch elm disease (Ophiostoma novo-ulmi Brasier) some fifty years ago. The bending MOE was determined in the longitudinal direction and the angles between the direction of load and the annual growth ring orientation were 0°, 45°, and 90°. The obtained values of the bending modulus of elasticity are within the range of those obtained for a recent elm, which shows that numerous centuries spent in anoxic aquatic conditions have not affected the investigated property of subfossil elm. The study showed that the annual growth ring orientation significantly affects the MOE of subfossil elm wood in the longitudinal direction. The highest values were obtained at the angle of 45° (L45°), and the values for L0° and L90° are very similar. The variability and heterogeneity of the MOE was described with the two-parameter Weibull distribution and the results follow the Weibull distribution.

WOOD RESEARCH Volume 63, Number 2, 2018
Hervice Kouefouet, G. Bawe, C.M. Fouotsa Woutsop, P. K. Talla, J.A. Mukam Fotsing, and E. Foadieng

Probabilistic approach of the failure of Lovoa trichilioides and Triplochiton scleroxylon

The aim of this work is the probabilistic modeling of the failure of Lovoa trichilioides and Triplochiton scleroxylonspecies. A general presentation of the wood while focusing on the Weibull distributions was carry out. Parameters of the Weibull distribution for each of the materials were determined. We remark that when the Weibull shape parameter is small, the failure stresses dispersion is greater and the Weibull scale parameter increase or decrease depending on the stress. It is also shown that Lovoa trichilioides exhibits a high dispersion of breaking stress in contrast to Triplochiton scleroxylon. A comparison of the experimental data with the statistical laws allowed us to show that the three-parameter Weibull distribution better models the failure than the normal and the two-parameter Weibull distributions. The studies of variance prove that the failure stresses of Triplochiton scleroxylon vary less in comparison with that of Lovoa trichilioides.