A modelling method is proposed to highlight the effect of cambial age on the effective modulus of elasticity of laminated veneer lumber (LVL) according to bending direction and veneer thickness. This approach is relevant for industrial purposes in order to optimize the performance of LVL products.
LVL is used increasingly in structural applications. It is obtained from a peeling process, where product’s properties depend on cambial age, hence depend on radial position in the log.
This study aims to highlight how radial variations of properties and cambial age impact the mechanical behaviour of LVL panels.
An analytical mechanical model has been designed to predict the modulus of elasticity of samples made from poplar LVL panels. The originality of the model resides in the integration of different data from the literature dealing with the variation in wood properties along the radius of the log. The simulation of the peeling process leads to veneers with different mechanical properties, which are randomly assembled in LVL panels.
The model shows a correct mechanical behaviour prediction in comparison with experimental results of the literature, in particular with the decrease in MOE in LVL made of juvenile wood. It highlights that the bending direction and veneer thickness have no influence on the average MOE, but affect MOE dispersion.
This paper proposed an adequate model to predict mechanical behaviour in the elastic domain of LVL panels based on the properties of raw wood material.
The effects of veneer orientation and loading direction on the mechanical properties of bamboo-bundle/poplar veneer laminated veneer lumber (BWLVL) were investigated by a statistical analysis method. Eight types of laminated structure were designed for the BWLVL aiming to explore the feasibility of manufacturing high-performance bamboo-based composites. A specific type of bamboo species named Cizhu bamboo (Neosinocalamus affinis) with a thickness of 6 mm and diameter of 65 mm was used. The wood veneers were from fast-growing poplar tree (Populus ussuriensis Kom.) in China. The bamboo bundles were obtained by a mechanical process. They were then formed into uniform veneers using a onepiece veneer technology. Bamboo bundle and poplar veneer were immersed in water-soluble phenol formaldehyde (PF) resin with low molecular weight for 7 min and dried to MC of 8–12 % under the ambient environment. All specimens were prepared through hand lay-up using compressing molding method. The density and mechanical properties including modulus of elasticity (MOE), modulus of rupture (MOR), and shearing strength (SS) of samples were characterized under loading parallel and perpendicular to the glue line. The results indicated that as the contribution of bamboo bundle increased in laminated structure, especially laminated on the surface layers, the MOE, MOR and SS increased. A lay-up BBPBPBB (Bbamboo, P-poplar) had the highest properties due to the cooperation of bamboo bundle and poplar veneer. A higher value of MOE and MOR was found for the perpendicular loading test than that for the parallel test, while a slightly higher SS was observed parallel to the glue line compared with perpendicular loading. Any lay-up within the homogeneous group can be used to replace others for obtaining the same mechanical properties in applications. These findings suggested that the laminated structure with high stiffness laid-up on the surface layers could improve the performance of natural fiber reinforced composites.
Cross-laminated timber (CLT) has recently emerged as a new wood product that utilizes a large quantity of domestic lumber. This study aims to analyze the effects of width and lay-ups on the tensile strength of CLT. To this end, the elastic modulus of sugi CLT with different lay-ups was measured by dynamic and static methods. Moreover, tensile tests were conducted for different widths and lay-ups of CLT. Results indicate that the apparent bending Young’s modulus, as calculated using the dynamic method, is directly proportional to the measured Young’s modulus in static method for each lay-up. Furthermore, there was no significant effect of width on the tensile strength in the range of 150, 300, and 600 mm. However, the variations in lay-ups affected the tensile strength as follows: CLT with larger ratio of the major strength direction lamina along the cross-section and with higher grade of lamina in the major strength direction showed higher tensile strength. The estimated tensile strength of CLT, as calculated using the Young’s modulus of the lamina of each layer, and the tensile strength of lamina as simple substance was found to be in good agreement with the measured tensile strength of CLT.