Southern pine and spotted gum are two of Australia’s most important locally produced commercial timbers. However, internationally, they are amongst the most problematic species to glue cost-effectively, especially for sawn-laminate-based structural engineered wood products, such as glulam and cross-laminated timber. This study investigated the efficacy of different pre-gluing wood surface machining preparations on the tensile shear strength of lap shear samples prepared from both species. Surface machining methods tested included planing, face milling, and sanding post-planing with 40 and 80 grit sandpaper. Wood face milling is not currently used commercially in Australia and has not previously been adequately tested on Australian commercial timbers to improve wood adhesion. Planing is currently the most common method used internationally for preparing wood surfaces for gluing. For both species, face milling with fast feed speed (45 m/min), slow cutter speed (57 m/s), and sanding treatments post-planing resulted in significantly higher tensile shear strength compared to planing for lap shear samples that had been subjected to an accelerated weathering process. Performance differences in tensile shear strength between surface machining methods are likely to be related to the effects of these machining methods on surface roughness, fibrillation, and sub-surface cell damage.

Darwin stringybark (Eucalyptus tetrodonta) is one of Northern Australia’s most important commercial forest resources. The wood exhibits desirable wood properties including high strength, natural durability, and visual appeal. The production of engineered wood products (EWPs) such as glulam from this resource represents a significant commercial opportunity for the timber industry in northern Australia. However, a major challenge to overcome is the achievement of satisfactory glue bond performance. This study evaluated the effects of different surface machining preparations, adhesive types, and curing temperatures on the bonding characteristics of Darwin stringybark. The pre-gluing surface machining method significantly influenced the timber wettability, roughness, permeability and tensile shear strength of adhesive bonds. Planing resulted in the lowest wettability, roughness, and permeability, while bonded planed samples produced the poorest tensile shear strength. Alternative surface machining methods including face milling and sanding post-planing were shown to significantly improve the timber wettability, roughness, and permeability, and also to increase the tensile shear strength of bonded samples. The resorcinol formaldehyde adhesive resulted in slightly improved tensile shear strength in most cases compared to the polyurethane adhesive. There was no significant improvement in tensile shear strength with the use of elevated temperature curing.

Drying has a major impact on the viability of sawn timber production, particularly through its influence on productivity, energy usage, and product quality. Traditionally, plantation-grown southern pine structural grade timber from Australia has been dried using high temperature (≥ 180 °C) conventional batch kilns. However, the Australian industry is showing increasing interest in continuous drying kilns because of reported cost savings and potential improvements in product quality. This study investigated the differences between continuous drying and conventional drying schedules on the radial permeability, wettability, gluability, and treatability of southern pine timber from Queensland plantations. The high temperature drying resulted in significantly lower liquid permeability compared to low temperature drying; however, there were no significant differences between drying schedules for gas permeability. For combined wood surface and core data, there were no significant differences in liquid permeability between low temperature drying and continuous drying or between continuous drying and high temperature drying schedules. For earlywood after surface machining, continuous drying resulted in the greatest wettability (based on K-values), whereas for latewood after surface machining, low temperature drying produced the greatest wettability. Earlywood had greater wettability compared to latewood. Continuous drying resulted in better gluability and treatability compared to conventional drying schedules.

Transverse modal analysis of timber panels is a proven effective alternative method for approximating a material's elastic constants. Specific testing configurations, such as boundary conditions (BC) and location of sensor and impact, play a critical role in the accuracy of the results obtained from the experimental assessment. This article investigates signal-specific details, such as the signal quality factor, that directly relate to the damping properties and internal friction as well as frequency shifting obtained from six different BCs. A freely supported (FFFF), opposing minor sides (shorter length) simply supported, and major sides (longest length) free (SFSF), as well as the reverse of the SFSF configuration with minor sides free and major lengths simply supported (FSFS) and all sides simply supported (SSSS) setup, are investigated. Variations into the proposed methods used to achieve an FFFF supported system are also considered. A combination of experimental testing in parallel with finite element analysis was conducted to re-create the setup that would be used within a manufacturing facility for nondestructive assessment of full-size cross-laminated timber panels. The differences between all BC configurations for their resonance frequency quality and location indicate that a freely supported system provides higher-resolution results, good comparison of less than 10 percent error with the finite element analysis and experimental results, and advantages in a simple experimental setup for the intended application.

No abstract