Thermally modified timber (TMT) is characterized by improved durability and dimensionally stability, but strength properties, especially the dynamic ones, are compromised at the same time. Because dynamic standard tests require high efforts and time, the high-energy multiple impact (HEMI) –test was developed for the fast and reliable characterisation of the structural integrity of TMT, showing a strong correlation of decreasing structural integrity with rising treatment intensity. Since the number of wood species subjected to this test method was limited up to now, 14 soft- and hardwoods were heat treated by ten different treatments at 180 and 220°C and used for determination of the structural integrity. The results showed temperature dependent strong correlations of decreasing structural integrity with increasing intensity for all species tested, pointing to the general applicability of the destructive HEMI-test in the frame of the post production quality control of TMT. In addition, the structural integrity is not affected by density, anatomical macro-defects like drying cracks, growth ring and fibre deflection or weathering impacts, which confirms its usage for implementation within a reliable factory production control to ensure constant product qualities.

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