Interrelationship between Static a nd Dynamic Strength Properties of Wood and its Structural Integrity

Various biotic and abiotic agents affect the performance of wood products. Chemicals, thermal energy, radiation, as well as different organisms have the potential to alter the optical, haptic and functional performance of wood. These effects come along with a change of structural integrity of wood, which in turn affects its strength properties. Therefore, a test was developed to quantify the structural integrity of wood in terms of its Resistance to Impact Milling (RIM). In a High-Energy Multiple Impact (HEMI) – test, steel balls were used in a heavy vibratory mill for crushing wood samples. Thousands of single events were captured by analyzing the fragments. Based on the degree of integrity and the percentage of fine fragments (< 1mm), an indicator has been defined to detect structural changes on cell wall level with high sensitivity. The aim of this study was to investigate the variation of structural integrity within and between ten different wood species in comparison with some strength properties according to standardized test protocols and in dependence of wood density. HEMI-tests, bending tests, and impact bending tests were performed with matched specimens. Wood density turned out to have only a subsidiary effect on structural integrity, but is dominanting standard strength properties. Thus, RIM was found to be only slightly correlated with the impact bending strength (IBS) and bending strength (MOR). On the other hand, the method shows clear insensitivity to natural variation in anatomy of wood.