Simulation Based Modeling of the Elastic Properties of Structural Composite Lumber

Structural composite lumber (SCL) products were introduced into the construction practice several decades ago. Their apparent advantages over traditional lumber did not generate copious research interests. However, increasing demands for structural materials coupled with the decreasing quality and quantity of raw materials are forcing the industry to introduce short rotation trees or species having unfavorable properties into the manufacturing processes. Consequently, there is a need for research to further enhance the effective use of renewable natural resources.This article describes the development of simulation models that estimate the bending and orthotropic compression modulus of elasticity (MOE) of laminated veneer lumber (LVL) and parallel strand lumber (PSL). The Monte Carlo simulation-based routines use the physical/mechanical properties of primary constituting elements, obtained from probability distributions, to calculate a particular property of the composite system. Furthermore, the orthotropic behavior of the wood constituents due to their position in the composite is modeled by well-established theoretical/empirical equations. Results and experimental validation regarding the geometric, physical, and mechanical attributes showed reasonably good agreement between simulated and experimental values. Developed models have good potential for predicting the elastic parameters of composites using new raw materials or novel design features

Finite Element Analysis of Cross-halved Joints for Structural Composites

The strength and stiffness of a notched, cross-halved joint was investigated using a three-dimensional finite element method (FEM). Composites involved in this research were laminated veneer lumber (LVL) and laminated strand lumber (LSL). The joint consisted of primary and secondary load-carrying elements notched and inserted into each other crosswise. A 3-D FEM technique predicted the deformations and stress developments under concentrated and distributed loads. Experimental validation of the model, based on deformation measurements, showed good to excellent agreement between predicted and measured values. Failure mode analysis revealed that the normal stresses (tension) control the performance of the joint.The joint configuration can provide additional lateral stiffness and stability in structural applications including floor and roof systems. Furthermore, the in-plane moment resistance of the joint may provide better performance of such structures under dynamic loads such as earthquakes and excessive wind loads

A Model for Viscoelastic Consolidation of Wood-Strand Mats. Part I. Structural Characterization of the Mat Via Monte Carlo Simulation

A procedure using Monte Carlo simulation was developed to characterize the spatial structure of randomly formed, wood-strand mats. The simulation reproduces the number of strands in the centroids of imaginary strand columns of finite size. The vertical distances between the adjacent strands and the location of the column centroid relative to the constant length of each strand are also simulated. A data base was collected on realistic mats produced from strands of constant size and non-planar geometries (i.e., random bow, cup, and twist). The procedure can be used in a model for predicting the mechanical behavior of random strand mats during consolidation

A Model for Viscoelastic Consolidation of Wood-Strand Mats. Part II: Static Stress-Strain Behavior of the Mat

A solid mechanics model is developed to predict the static stress-strain behavior of randomly formed wood-strand mats during pressing. The procedure includes a Monte Carlo simulation for reconstructing the mat structure. During the early stages of mat displacement, the model computes the cumulative stress development from strand bending. As consolidation continues, the overlapping strands form solid columns. Hooke's Law, modified by a nonlinear strain function, governs the stress development in a finite number of these imaginary columns comprising the mat. Experimental results showed good agreement with the predicted stress response

Product Development from Veneer-Mill Residues: An Application of the Taguchi's Method

The raw material used for decorative (face) veneer manufacturing consists mainly of hardwood logs, the highest in quality harvested for industrial purposes. Besides the common sawmill residuals, the clipping operation in the process produces quite long, strand-type vestiges, and large end-clipping cutoffs. During the course of the research project presented in this article, structural composite materials were designed and formulated using these clipping residues as principal furnish materials. A robust statistical product development technique, the Taguchi's method, helped to identify the effect of component factors on the expected mechanical properties of these novel products.Results of three-factor/three-level analyses indicated that there is a linear positive correlation between target density and performance attributes (MOE and MOR). Increasing the content of end-clippings up to 25% resulted in decline of strength and stiffness. However, when the ratio was over 1 to 4, this trend proved to be negligible. Resin solid content within the selected range had no significant control over the examined panel properties

Orthotropic Strength and Elasticity of Hardwoods in Relation to Composite Manufacture. Part I. Orthotropy of Shear Strength

The orthotropy of apparent shear strength of three Appalachian (aspen, red oak, and yellow-poplar) and two East European (true poplar and turkey oak) hardwood species was investigated. The experimental approach included shear force applications in planes parallel to the grain so that the annual ring orientation and the orientation of the grain relative to the applied force direction were systematically rotated. Statistical analyses of results demonstrated significant effects of grain and ring orientation on the shear strength for all species. Furthermore, interaction between these two factors was detected. Three models, developed to appraise the orthotropic nature of shear strength, were fitted to experimental data demonstrating acceptable to good agreement between predicted and experimental values. A combined model based on tensor theory and a modified version of Hankinson's formula provided the best fit by r2 analysis. The information obtained and the models developed might be used to explore the shear strength of structural composites in which the constituents are systematically or randomly aligned

Orthotropic Strength and Elasticity of Hardwoods in Relation to Composite Manufacture Part III: Orthotropic Elasticity of Structural Veneers

Structural veneers approximately 3.2 mm (1/8 in.) in thickness are widely used as basic constituents in structural composites such as plywood, laminated veneer lumber (LVL), and parallel strand lumber (PSL). The veneer processing operation (peeling) may adversely alter the mechanical properties of the wood substance by introducing compression-set, cracks, and splits, etc. The modulus of elasticity (MOE) in tension of five hardwood species, which are potential raw materials for composite manufacture, was investigated in veneer form. The experimental work included dynamic MOE determination using ultrasound stress wave timing and static MOE measurements for comparison purposes. The orthotropy of MOE in the longitudinal-tangential (LT) plane was also a target of the investigation. Theoretical models were fitted to experimental data that may predict the MOE of the constituents according to their position within the consolidated composites. Experimental and analytical results indicated that a combined model including the Hankinson's formula and an orthotropic tensorial approach is the best estimator for MOE of veneers having inclined grain orientation. Furthermore, the relationship between static and dynamic MOE values may be obtained by second-order polynomial models