Moment-Curvature Analysis of Coupled Bending and Mechanosorptive Response of Red Spruce Beams

In this study, an expanded comprehensive numerical approach to predict hygromechanical behavior of beams is proposed that rigorously couples spatially varying time-dependent moisture content fluctuation with uniaxial stress-strain relations. The constitutive model, consisting of elastic, viscoelastic, and two mechanosorptive strain elements connected in series, was used in a layered moment-curvature flexural analysis. The procedure is numerical and is able to take into account effect of moisture content changes, different mechanosorptive behavior in tension and compression, and cross-sectional hygroexpansion. The overall trend and magnitude of predicted deflections are in good agreement with experimental results. Results demonstrated that complex beam behavior in a varying environment can be predicted by a simple model with well-defined material characteristics generated through relatively simple 18-h uniaxial experiments

The Effect of Chemical Changes during Heat Treatment on the Color and Mechanical Properties of Fir Wood

European silver fir (Abies alba L.) wood was heat-treated in an oven for 60 min at seven different temperatures of 100 °C, 150 °C, 200 °C, 220 °C, 240 °C, 260 °C, and 280 °C under atmospheric pressure in the presence of air. The effect of thermal treatment on the chemical composition, mechanical, and color properties of the wood was studied, and the mutual correlations between the investigated properties were evaluated. The bending strength/modulus of rupture (MOR) and the modulus of elasticity (MOE) were positively correlated with the total saccharides, glucose, mannose, and xylose content, where R ranged from 0.942 to 0.984. For changes in the wood color, very strong positive correlations between the total color difference and the contents of lignin and extractives were determined, where R = 0.968 and 0.945 respectively. Additionally, the total color difference was negatively correlated with the total saccharides, mannose, and xylose content, where R ranged from 0.876 to 0.938. The obtained data were evaluated by principal component analysis (PCA), where the components explained 93.1% of the total variance

Measuring the Modulus of Elasticity of Thermally Treated Spruce Wood using the Ultrasound and Resonance Methods

The effect of thermal treatment temperatures on the dynamic and static modulus of elasticity (MOE) of Norway spruce wood (Picea abies (L.) H. Karst.) was evaluated. The dynamic MOE was measured using ultrasound and resonance methods in the longitudinal and transverse directions. The static MOE was determined by the three-point bending test. The dynamic MOE values determined by the ultrasound method were higher than the static MOE values in each case. As the temperature of the thermal treatment increased, the difference between the dynamic and static MOE values decreased. The MOE increased with increasing temperature, and it was more pronounced on a tangential surface. Increasing the sensor distance had a positive effect on the correlation between the static and dynamic MOE, and the effect from the increased temperature decreased. Measurement by the resonance method showed twice as high MOE values in the transverse direction than in the longitudinal direction. The thermal treatment caused a significant decrease in the MOE only in the transverse direction, and the differences were insignificant in the longitudinal direction. The dynamic MOE values measured by the resonance method were higher than the static MOE values but slightly lower than the values measured by the ultrasound method

Novel hybrid polymer adhesives for laminated materials based on hardwood

Gluing hardwood with standard adhesives often appears problematic; therefore, their broader use in practice is limited. On the other hand, using hardwood in laminated beams would undoubtedly benefit because mechanical properties would reduce construction dimensions compared to commonly used materials. The hardwood surfaces are highly heterogeneous and porous structure, and the high tannin content in heartwood restrict the use of standard structural PUR adhesives. Using modified adhesives is one of the possibilities to overcome these problems. This work deals with PUR adhesive based on polymeric methylene diphenyl diisocyanate (C15H10N2O2). For this specific PUR adhesive, three different application methods were used (pure polyurethane adhesive as a reference, the adhesive system with application of deep penetration, and the adhesive system with application of deep penetration with an admixture of thermoset particles (C7H6O) and polyurethane adhesive). Such a combination of a particular adhesive with a thermoset increases adhesive parameters, especially for hardwood. Above glass transitions point Tg of the thermoset resin, a 3D network between the thermoset and PUR is formed as a novel species which appears highly resistant to moisture. This protocol has been verified on glued surfaces of several difficult-to-glue types of wood, such as oak (Quercus robur), beech (Fagus sylvatica), and black locust (Robinia pseudoacacia). A lap joint shear strength test using a joint test according to EN 302-1 [1] was used to determine the mechanical properties of the adhesives. The results of lap joint shear strength tests are deter-mined based on the classification standard EN 15425 [2]. Based on the collected results, it is possible to confirm the positive effect of adhesives modified by thermosets on the overall strength of the glued joints in the longi-tudinal direction of the laminates.Web of Science308art. no. 11668