Comparison of the bending solidities of European beech, Black poplar, Norway spruce and Douglas fir using DIN 52186 and fractometer 1 methods

The bending solidity of 24 stem sections of the species beech. poplar, spru ce and Douglas fir were investigated by using the DIN-52 186 (Fig. 1) and t he fractometry methods (Fig. 2). In spite of the relative small spot-check it is possible to characterise the fractometer 1 as useful or useless instr ument for assessing the ultimate strength of tree stems. The important resu lts are: 1. There is no correlation between the DIN bending solidity and the fractom etry-delamination values (Fig. 6). 2. Wood samples from different tree species with similar bendings strength values may show very different fractometer-delamination values (Fig. 5). 3. On wood samples of spruce and poplar with normal bending solidities (58- 95 N/mm(2), 45-70 N/mm(2)) the fractometer delamination values layed near z ero (Fig. 6, Tab. 1, 3-5). 4 Contrary to this the relations of the DIN/fractometer bending solidities on beech samples were normal (Tab. 1,2). Therefore the use of the fractometry method (fractometer I) is sen; nan ow limited and therefore not recommendable for assessing the tree's ultimate s trength.