Evaluation of non-destructive test methods for predicting the static bending stiffness and strength properties of thermally modified timber

Abstract: Non-destructive technologies have been applied on predicting the stiffness and strength properties of timber for decades. However, these technologies have rarely been investigated on predicting the properties of thermally modified timber. This study was performed to investigate the non-destructive technologies on estimating of the strength and stiffness properties of thermally modified timber. The material that was utilized for study is full-size structural Norway spruce. Twenty-five thermally modified boards were investigated by applying both non-destructive technologies and static bending test; 25 unmodified boards were used as a control group. Timber grader MTG and Sylvatest Trio are two non-destructive tools that were used for the determining the modulus of elasticity (MOE): MTG is an application of resonance frequency technology and Sylvatest Trio is an application of time-of-flight technology (TOF). The results show that both non-destructive technologies provide good results (??2=0.70 from MTG and??2=0.58 from Sylvatest Trio) on estimating the stiffness properties while poor resultson predicting the strength properties of thermally modified boards.The result shows anoverestimation of modulus of elasticity (MOE) from time-of-flight test compared withthe MOEs gathered from static bending test and resonance frequency test for both thermally modified boards and unmodified ones. The stiffness properties of boards after thermal modification reduced slightly (6.5%) compared with unmodified timbers; while strength properties of thermally modified boards decreased (37.5%) significantlycompared with control group.This study is a part of a bigger study performed at Linneaus University by Joran vanBlokland.