Ermittlung ausgewählter mechanischer Kennwerte thermisch modifizierter Buche

Abstract

Untersuchungen zu physikalisch‐mechanischen und chemischen Eigenschaften thermisch modifizierten Holzes sind bereits seit den frühen 1950er Jahren durchgeführt und wieder verstärkt in den letzten zehn bis zwanzig Jahren aufgenommen worden. Generelle Zusammenhänge zwischen den Behandlungsparametern und den Eigenschaften des vergüteten Holzes sind weitgehend bekannt. Gegenstand und Ziel der vorliegenden Untersuchungen war die Ermittlung ausgewählter mechanischer Kennwerte von im Autoklaven nach zwei unterschiedlichen Verfahren thermisch behandeltem Buchenholz. Die Resultate zeigen, dass die Zug‐ und Druckfestigkeit sowie der Elastizitäts‐ und Schubmodul im Vergleich zum unbehandelten Referenzholz um bis zu 50 % sinken. Die Zugfestigkeit wurde dabei stärker beeinträchtigt als die Druckfestigkeit. Determination of select mechanical properties of heat‐treated beech wood. Studies on mechanical and chemical properties of heat‐treated wood have been conducted since the early 1950ies. General interrelationships between process parameters and properties of heat‐treated wood are reasonably well known. The present study deals with select mechanical properties of heat‐treated beech wood in the autoclave in two different treatment atmospheres. The results show, that the tensile and compression strength as well as modulus of elasticity and modulus of rigidity decrease about 50 % compared to untreated wood. The tensile strength was less affected by the treatment than the compression strength.

Characterisation of thermally treated beech and birch by means of quasi-static tests and ultrasonic waves

“…The results of this study reveal that Young’s moduli obtained from tension were higher than those from compression tests for reference and thermally treated beech and birch. This trend is similar to that obtained by Wetzig et al 36 , where greater E L values from tensile than compression tests were obtained for heat-treated and untreated beech. This tension–compression asymmetry of wood elastic properties was also noticed for untreated beech 37 and for untreated walnut and cherry wood 38 , 39 .…”

“…Overall, the Young's moduli from ultrasonic tests have higher values than those obtained from quasi-static tests in all directions. This general tendency is well documented in the literature 36,41,42 . This difference, however, is more noticeable in the radial direction (up to 75% and 107% higher values obtained by ultrasound for beech and birch, respectively).…”

“…Poisson's ratio (v LR ) values reported in literature seem to be insensitive to thermal treatment, with no clear correlations between these values and intensity of treatment 20,36 . In contrast, v LR values of treated samples obtained in this study appeared to have lower values compared to untreated beech and higher values compared to reference birch.…”

“…V ii 2 ) from ultrasounds (e.g. Wetzig et al 36 ). Now, inspection of the C values for reference beech and birch (listed in Table S2 in the supplementary material; C 11(beech) = 23.7; C 11(birch) = 21.4 GPa) clearly shows that the simplified analysis method overestimates the Young’s moduli of wood and it is therefore strongly recommended to use the full stiffness inversion method when determining the elastic modulus from ultrasonic tests.…”

Effects of removal of extractives on the chemical composition and mechanical properties of wood

“…When Missanjo and Matsumura (2016) studied the relationship between wood density and mechanical properties, they found that wood density had a significant positive correlation with bending strength. In addition, Wetzig et al (2011) reported that wood density had an important effect on tensile strength, and the strength was increased with the increase of density. Therefore, the change in tensile strength and bending strength of pine wood after extraction was mainly caused by the change of density.…”