Progress 08/15/03 to 08/14/07
Outputs
In the project, properties of wood strands generated from small-diameter trees removed from southern forests were studied to determine the influence of wood species, material type, and thermal processing on the composite properties. A combined approach of x-ray CT scanning and finite element (FE) modeling was used to characterize engineering properties of oriented strandboard (OSB). Tests on strand properties showed that tensile strength and dynamic storage moduli increased with the increasing strand density. A large variation in both properties was observed for southern pine, whereas willow strands showed much smaller variability. The dynamic moduli of strands decreased with increasing temperature. High-density strands were thermally more stable than low-density strands. Hot pressing and resin application significantly affected the mechanical and dimensional performance of strands. These effects depended upon the strand thickness and location (face or core).
Three-layer OSB made of small-diameter southern pine trees showed satisfactory strength and dimensional stability properties. As the fines loading levels increased, linear expansion (LE) along the parallel direction decreased, while the LE value along the perpendicular direction and thickness swelling increased. With increased fines levels, the internal bond strength showed an increasing trend up to the 20% fines level, and bending strength and modulus varied little in the parallel direction and slightly decreased in the perpendicular direction. For mixed hardwood OSB, bending properties varied little in the parallel direction and decreased in the perpendicular direction as fines in the core layer increased. Parallel LE decreased and the perpendicular value increased with the increase of fines in the core layer. Predicted effective panel modulus and LE agreed well with the experimental data. Shifting a certain amount of fines from core to face layers led to more balanced panel
properties along the two principal directions. A method of building a model to represent internal structure of OSB based on x-ray tomography and image analysis was developed. OSB samples were scanned with an x-ray tomography machine and the internal structure of the composite was reconstructed into three dimensional images using advanced image processing techniques. In-plane density distribution and voids structure in OSB were generated from the analysis. A three layer FE model was created using the geometry model from X-ray tomography and image analysis reflecting actual microstructure of the testing samples to account for real density variation. Considering the variation of material properties due to considerable density variation of the OSB, each element was assigned a set of material constants according to the local density obtained from image processing. Orthotropic material properties were considered in the simulation. The predicted panel moduli showed reasonable agreement with
the experimental data. The study shows that OSB performance can be characterized numerically with FE simulation in combination with x-ray imaging analysis to achieve the goal of digital testing of structural wood composite material.
Impacts
The study provides further understanding of thermal and mechanical properties of southern pine and southern hardwood (e.g., willow) strands and properties of southern pine and mixed hardwood oriented strandboard (OSB) from small-diameter logs removed from the southern forests. The work establishes some basic relationships among wood strand mechanical properties, density, and processing temperatures; and the effects of strand quality (i.e., fines)and structural arrangement of wood strands with different dimensions on OSB's mechanical and dimensional stability properties. Analytical techniques developed from the study, which combine x-ray tomography with finite element simulation techniques, provide a fundamental advance in analyzing structural composite properties and in achieving digital testing of the wood-based composite material. The results of this work can help the OSB manufacturers optimize products and process, reduce the margin for manufacturing errors, and
increase their competitiveness in the marketplace.
Publications
- Han, G., Q. Wu, and J.Z. Lu. 2007. The Influence of Fines Content and Panel Density On Properties Of Mixed Hardwood Oriented Strandboard. Wood Fiber Sci. 39(1):2-15.
- Lei, Y., and Q. Wu. 2006. Cure Kinetics of Aqueous Phenol-Formaldehyde Resins Used for Oriented Strandboard Manufacturing: Effect of Wood Flour. Journal of Applied Polymer Science 101:3886-3894.
- Lei, Y., and Q. Wu. 2006. Cure Kinetics of Aqueous Phenol-Formaldehyde Resins Used for Oriented Strandboard Manufacturing: Effect of Zinc Borate. Journal of Applied Polymer Science 101:3886-3894.
- Lei, Y., Q. Wu, and K. Lian. 2006. Cure Kinetics of Aqueous Phenol-Formaldehyde Resins Used for Oriented Strandboard Manufacturing: Analytical Technique. Journal of Applied Polymer Science 100:1642-1650.
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Progress 01/01/06 to 12/31/06
Outputs
Thermal and mechanical properties of southern pine and willow strands and properties of southern pine oriented strandboard (OSB) from small-diameter logs were investigated in this study. The effect of density and species group on tensile strength, dynamic moduli, and thermal stability of wood strands, and of strand quality (i.e., wood fines) on three-layer OSB properties were also analyzed. Strand tensile strength and dynamic storage moduli increased with the increasing strand density. A large variation in both tensile strength and values were observed for southern pine, whereas willow strands showed much smaller variability. The dynamic moduli of strands decreased with increasing temperature in the range of 25 to 200oC. Small loss modulus peaks were observed over the temperature range studied. The strands with higher densities had higher loss modulus. Thermogravimetric analysis (TGA) results revealed that high-density strands were thermally more stable than
low-density strands. Three-layer OSB made of small-diameter southern pine trees showed satisfactory strength and dimensional stability properties. As the fines loading levels increased, linear expansion (LE) along the parallel direction decreased, while the LE value along the perpendicular direction and thickness swelling increased. With increased fines levels, the internal bond strength showed an increasing trend up to the 20% fines level, and bending strength and modulus varied little in the parallel direction and slightly decreased in the perpendicular direction.
Impacts
The study provides further understanding of thermal and mechanical properties of southern pine and willow strands and properties of southern pine oriented strandboard (OSB) from small-diameter logs.
Publications
- Han, G. P., Q. Wu, and Z. Lu. 2006. Selected properties of wood strand and oriented strandboard from small-diameter southern pine trees. Wood and Fiber Science 38(4):621-632.
- Han. G., and Q. Wu. 2006. Oriented strandboard from small diameter southern pine trees. Advances and challenges in biocomposites - Proc. the 8th Pacific Rim Bio-based composites symposium. Mohd Nor Mohd Yusoff et al. edited. ISBN 983-2181-87-9. Kuala Lumpur, Malaysia. pp110-120.
- Wu, Q., B. Zhang, L. Wang, and G. Han. 2006. The application of 3-D x-ray tomography with finite element analysis for engineering properties of strand based composites. Advances and challenges in biocomposites - Proc. the 8th Pacific Rim Bio-based composites symposium. Mohd Nor Mohd Yusoff et al. edited. ISBN 983-2181-87-9. Kuala Lumpur, Malaysia. pp200-209.
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Progress 01/01/05 to 12/31/05
Outputs
A three layer (two face layers and one core layer with different flake alignment level) finite element (FE) model was created to investigate engineering performance of OSB. The FE geometry model was based on X-ray tomography and image analysis reflecting actual microstructure of the testing samples to account for real density variation. The model has a total of 10,000 three-dimensional 8-node elements to simulate each quarter of the test sample. Pixel variation for each layer of the panel was generated with IDL programming. A FORTAN program was written to automatically import the pixel value variation and calculate elastic modulus based on established pixel-density correlation and density-elastic modulus relationships. It also generateed an ABAQUS input file and output request based on the information and intended simulation. Considering the variation of material properties due to considerable density variation of the OSB, each element was assigned a set of material
constants according to the local density obtained from image processing. Orthotropic material properties were considered in the simulation. The loading and boundary conditions were set to be the same as real test conditions of a uniaxial tensile test. The predicted panel moduli were compared with the experimental data, which showed reasonable agreement. The study shows that OSB performance can be characterized numerically with FE simulation to achieve the goal of digital testing of wood composite material.
Impacts
The results of this work can help OSB manufacturers optimize their raw material input and manufacturing processes through modeling to improve engineering performance of structural composite panels.
Publications
- Zhang, B., Q. Wu, L. Wang, And G Han. 2005. The Influence of In-Plane Density Variation On Engineering Properties of Oriented Strandboard: A Finite Element Simulation. In Proc. the McMat2005 - The 2005 joint ASME/ASCE/SES Conference on Mechanics and Materials. June 1-3, 2005. Baton Rouge, LA. Paper 257.
- Wu, Q., Cai, Z., and J.N. Lee. 2005. Tensile and dimensional properties of wood strands made from plantation southern pine lumber. Forest Products Journal 52(2):1-6.
- Zhang, B., Q. Wu, L. Wang, and G Han. 2005. Characterization of Internal Void Structure of Strand-Based Wood Composites Using X-Ray Tomography and Digital Tools. In Proc. the McMat2005 - The 2005 joint ASME/ASCE/SES Conference on Mechanics and Materials. June 1-3, 2005. Baton Rouge, LA. Paper 255.
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Progress 01/01/04 to 12/31/04
Outputs
Strand-based composites are formed by arranging flakes (or strands) in a mat and bonding them together with adhesives under heat and pressure. The performance of these products is governed by the properties of wood strands, adhesive, manufacturing strategy, and production process. A method of building a model to represent internal structure of oriented strandboard (OSB) based on x-ray tomography and image analysis was developed. OSB samples were scanned with an x-ray tomography machine and the internal structure of the composite was reconstructed into three dimensional images using advanced image processing techniques. Internal variations of material density were measured during image processing; and the voids and their distributions were identified and reconstructed. The in-plane and out-of-plane distribution of density and voids variations were presented numerically. It was found that the x-ray tomography and image processing technology can be used to obtain density
distribution and voids structure in OSB. The digital images can be used to generate the geometric model used for numerical simulation with finite element (FE) method. This model will take the material structure into account. A FORTRAN program has been developed to automatically read the density variation information from images and to build the model for the simulation with ABAQUS in the future work. In-plane density variation in OSB is an inherent property due to randomness in mat forming. It has been long known that the density variation affects engineering performance of the product. However, its effect on elastic properties of the OSB has never been fully understood. A finite element model which reflects sample internal structure was developed to calculate anisotropic engineering constants of OSB. In this work, elastic properties and in-panel stress concentrations of single-layer OSB under several density distributions and flake orientations were predicted using the finite element
model. A FORTRAN program was written to automatically create the simulation model in ABAQUS for sets of material property input. This can later be extended to other material models with specific loading history to reflect realistic conditions. It was found that the variation of in-plane density resulted in significant variation of localized stress concentrations, while the effect on elastic moduli and Poisson's ratio of OSB is slight. The FE model is the basis for future three-layer panel model combining the microstructure obtained through x-ray tomography and imaging analysis.
Impacts
The development of sound experimental technique and theoretical models for characterizing the performance of structural wood composites under different processing conditions will help the manufacturers optimize product and process, reduce the margin for manufacturing errors, and increase their competitiveness in the marketplace.
Publications
- Han, G., and Q. Wu. 2004. Comparative properties of comrind and wood strands for structural composite manufacturing. Forest Products Journal 54(12):283-294.
- Han, G., Q. Wu, and R. Vlosky. 2004. Mixed Sugarcane Rind and Hardwood Oriented Strandboard Bonded with Phenol Formaldehyde Resin. In Proc. the 7th Pacific Rim Bio-based Composite Symposium. Nanjing, China. October 31-Nov. 2, 2004. pp 115-125.
- Wu, Q., J.N. Lee, and G. Han. 2004. The influence of voids on the engineering constants of oriented strandboard: a finite element model. Wood Fiber Sci. 36(1):71-83.
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Progress 01/01/03 to 12/31/03
Outputs
Single and three-layer oriented strandboard (OSB) was manufactured using both mixed hardwoods and southern pine furnished from small diameter trees. Experimental variables include mat structure (single versus three-layer), density, fines content, and furnish type (i.e., from small and large diameter trees). Mechanical (i.e., bending modulus and strength and IB strength) and physical properties were measured and data is being analysed to examine the effect of several variables on panel properties. Further testing on tensile and shear moduli of the test panels are being conducted. Finite element models for both single and three-layer panels are being developed to model the internal void structure of the various panels. Void scanning technique using x-ray computer tomography is currently being developed for the panels.
Impacts
The development of sound experimental technique and theoretical models for characterizing the performance of structural wood composites under different processing conditions will help the manufacturers optimize product and process, reduce the margin for manufacturing errors, and increase their competitiveness in the marketplace.
Publications
- No publications reported this period
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