Non-destructive estimation of fibre angle in thin beech veneers using stress-wave derived dynamic modulus of elasticity

When sorting highly stressed wood-hybrid composites made of laminated veneer and plywood, both density and fibre orientation must be considered due to the pronounced anisotropy of wood. For the accurate design and dimensioning of components made from defect-free veneers, strength and modulus of elasticity must be estimated as precisely as possible using non-destructive methods. These properties are primarily influenced by the in-plane and out-of-plane fibre orientation. In this study, fibre orientation was estimated indirectly via the dynamic modulus of elasticity, determined from stress-wave transition time and density. A total of 327 beech veneers (Fagus sylvatica), each 0.9 mm thick, were analyzed. The veneers originated from 12 trees supplied by four different manufacturers and exhibited fibre orientations between 0° and 32.4°. As a reference, fibre orientation was determined optically using five measurements per specimen with a reflected-light microscope at 20× magnification. Based on the experimental data, a predictive model using Hankinson’s equation was developed and validated with an independent sample set (N = 22) from a fifth supplier. The model achieved a coefficient of determination of R² = 0.93 for the training set and R² = 0.74 for the validation set, demonstrating strong potential for future technical applications.