Strength and stiffness predictions with focus on different acoustic measurement methods
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ORIGINAL
Strength and stiffness predictions with focus on different acoustic measurement methods A. Kovryga1 · J. O. Chuquin Gamarra1 · J. W. G. van de Kuilen1,2 Received: 24 September 2019 © The Author(s) 2020
Abstract Strength grading is an important step for the production of homogenous and high-quality solid wood material. In particular, for hardwoods, the use of non-visible characteristics is indispensable. Dynamic MOE (Edyn) is an important parameter widely used for grading of softwoods and applicable to hardwoods as well. There are two common ways to measure Edyn—ultrasound (US) wave propagation and longitudinal vibration (LV) method. Both methods are used in practice, however, due to the different inherent measurement techniques, the results differ. The current paper analyses the stiffness and strength coefficients of determination for several temperate European hardwood species and emphasizes the differences between the two measurement systems. The performance was analysed with regard to grading techniques, testing modes for the mechanical properties (tension and bending) and wood qualities. For more than 2861 pieces of European ash (Fraxinus excelsior), European beech (Fagus sylvatica), European oak (Quercus spp.) and maple (Acer spp.), the Edyn was measured using both techniques, and destructive tests (tension and edgewise bending) were applied. The results show that LV has higher coefficient of determination compared to the US Edyn. The coefficient of determination for both methods and tensile application can be increased by calculating Edyn with average density. Furthermore, the results support species-independent strength grading of hardwoods. Further research on the effect of different wood qualities and sawing patterns is required.
1 Introduction Temperate hardwoods are very well known for their excellent mechanical properties, which make them favourable for structural purposes. As a naturally grown material, wood shows high variation in mechanical properties. Strength grading is a crucial step for the production of homogenous and high-quality solid wood material with defined material properties. Whereas the research on softwoods has led to the high acceptance of the machine strength grading methods, the application of those methods to hardwoods is less frequent. The research activities in recent years in the field of strength grading and engineered wood products aimed to bridge knowledge gaps with regard to hardwoods. Recent research activities have been focused on novel methods of non-destructive testing, as well as applying the * A. Kovryga [email protected] 1
Department of Wood Technology, Technical University of Munich, Winzererstrasse 45, 80797 Munich, Germany
Faculty of Civil Engineering and Geosciences, Delft University of Technology, Delft, The Netherlands
2
established methods of machine strength grading to hardwoods. In focus of the mechanical strength grading, the dynamic MOE (Edyn) can be highlighted as a major criterion of interest. Edyn is a mechanical property of the ma
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