European beech log and lumber grading in wet and dry conditions using longitudinal vibration

Abstract

In Central Europe, European beech (Fagus sylvatica L.) is the most frequently occurring hardwood species. An efficient grading method has the potential to promote its utilisation as construction material. Wood density, eigenfrequency and length were measured in 99 European beech logs for calculating the dynamic modulus of elasticity (MOE_dyn) obtained by longitudinal vibration (resonance). In addition, the log taper was measured. Of those logs, 867 boards were cut using a bandsaw. The MOE_dyn in green condition was determined on 505 of the boards and the MOE_dyn in dry conditions was determined on all of them. The r² value between the MOE_dyn of a log and the mean of MOE_dyn of its boards was 0.72 in the wet condition. The MOE_dyn,12% of boards significantly increased by 88 N mm^-2 for each centimetre away from the pith. The negative effect of log taper on MOE_dyn of boards was barely significant (P-value = 0.050). The MOE_dyn,12% was highly dependent on the MOE_dyn,wet (r² = 0.83) and was 17% higher than the MOE_dyn,wet. The mechanical properties of European beech timber exceed those of European softwood species. However, the relationships regarding MOE_dyn between different grading levels in the processing chain appear to be similar to those of softwoods.