Machine Grading of High-Density Hardwoods (Southern Blue Gum) from Tensile Testing

Abstract

Hardwoods commonly have high mechanical properties, which makes them interesting for structural use, but softwoods dominate the structural timber market in Europe. Tensile strength classes are recommended for engineered wood products. However, current European standards do not provide tensile strength classes for hardwoods and the declaration of tensile properties from machine grading in the industry is not yet possible. The present paper aims to contribute to the revision of European standards through the technical group CEN/TC124/WG2/TG2: Tensile strength classes for hardwoods, of the European Standardisation Committee. An experimental campaign which involved machine grading and tensile testing of over 569 boards of Southern blue gum (Eucalyptus globulus Labill.) from Spain and Portugal was made. Six new tensile strength classes were defined, from ET24 (ft,0,k = 24 N/mm2, Et,0,m = 18 kN/mm2 and ρk = 590 kg/m3) to ET42 (ft,0,k = 42 N/mm2, Et,0,m = 23 kN/mm2 and ρk = 640 kg/m3). Machine grading made possible the definition of six strength class combinations. Four combinations resulted in 40% of the sample being assigned to the higher strength class, with low percentages of rejection (varying between 1% and 14%). This demonstrates the high mechanical properties of the species and the performance improvement of machine grading with respect to current visual grading.

The Challenge of Strength Grading UK Hardwoods

“…Hardwoods can also be assigned to tension T-classes, but research suggests that separate hardwood T-classes would be more appropriate [36,37,42]. However, different studies suggest markedly different strength class profiles depending on the tested species.…”

“…Hardwoods have long been neglected as a modern structural material, but their increasing availability and outstanding mechanical properties have prompted researchers in various European countries to characterise the properties of local hardwood species [15,21,36,42,46,52,56]. Six new species-origin combinations will be added to the new version of EN 1912 [17] for European hardwoods, complementing the existing six visual grading assignments of European hardwood species, various machinegrading assignments and technical approvals for engineered wood products [1].…”

Analysis of the treatability, water repellency efficiency, and dimensional stability of maritime pine after microwave drying

“…Sawn wood production on a global scale is presently concentrated on softwood species. Projections indicate that by 2030, approximately half of all softwood production will be allocated for utilization in the construction industry, thereby substituting for steel, concrete, and masonry (Nepal et al 2021;Martins et al 2023). Besides the wide use of solid wood elements, engineered wood elements, for example, cross-laminated timber (CLT), are undergoing a fast increase in use in the contemporary market and are becoming very popular and used in different construction projects around the globe (Pramreiter et al 2023).…”