Wood Composite Warping: Modeling and Simulation

Warping, which is defined as the out-of-plane deformation of an initially flat panel, is a longstanding problem associated with secondary manufacturing processes in the wood panel industries. The mechanism of warping is still not fully understood. Unlike previous modeling, this study has developed a new twodimensionaal warping model based on mechanics of layered composites. Wood composite panel is regarded as a multilayered composite material in which each layer has different properties, especially when they experience moisture gradient through their thickness. Detailed model development and computer simulation results are presented. Panel parameters such as thickness. MOE, LE, Poisson's ratio, shear modulus, density, and orientation of layer were simulated; and quantitative relationships between these parameters and warp were presented. The results should provide a better understanding of wood composite warp

Formation of Nanocarbon Spheres by Thermal Treatment of Woody Char from Fast Pyrolysis Process

Influences of thermal treatment conditions of temperature, reaction cycle and time, and purge gas type on nanocarbon formation over bio-chars from fast pyrolysis and effects of thermal reaction cycle and purge gas type on bio-char surface functional groups were investigated by temperature-programmed desorption (TPD) and temperature-programmed reduction methods. Nanospheres occurred on bio-chars under the activation temperature of 700°C; more nanospheres occurred when temperature increased to 900°C. Further increase of temperature to 1100°C yielded bio-char surfaces covered with a layer of nanospheres between 20 and 50 nm. More carbon nanospheres formed by increasing thermal cycles and reaction time. Scanning electron microscope images of char surfaces showed there were fewer or no nanoparticles produced using H2 as the purge gas and they were porous. TPD results indicated that H2, H2O, CH4, CO, and CO2 in gas phases evolved from chars heated to 1000°C during the first heating cycle. H2 and CH4 peaked at 750 and 615°C, respectively. Both H2O and CO had two peaks, and CO2 had a broad peak. Only trace amounts of H2 and CO were detected in the second cycle. There was no detection for CH4, H2O, and CO2 after the second cycle

Simplified analytical model and balanced design approach for light-weight wood-based structural panel in bending

AbstractThis paper presents a simplified analytical model and balanced design approach for modeling light-weight wood-based structural panels in bending. Because many design parameters are required to input for the model of finite element analysis (FEA) during the preliminary design process and optimization, the equivalent method was developed to analyze the mechanical performance of panels based on experimental results. The bending deflection, normal strain and shear strain of the panels with various configurations were investigated using four point bending test. The results from the analytical model matched well with the experimental data, especially, the prediction for maximum deflection of the panels under failure load. The normal strain and shear strain calculated by the model also agreed with the experimental data. The failure criterion was determined by the failure modes using a 3-dimensional diagram with apparent normal and shear strain. For demonstration, panels 1 and 2 with a fixed core were modeled using the balanced design approach for optimal face thickness. The results showed that both the 3-dimensional diagram and analytical model provided similar thickness results, which were verified by the FEA for wood-based structural panels

Adaptive mesh refinement based simulations of three-dimensional detonation combustion in supersonic combustible mixtures with a detailed reaction model

Detonation combustion initiated with a hot jet in supersonic H2-O2-Ar mixtures are investigated by large-scale three-dimensional (3D) simulations in Tianhe-2 computing system with adaptive mesh refinement method. The reactive Euler equations are utilized as the governing equations with a detailed reaction model where the molar ratio of the combustible mixture is 2:1:7 under the condition of pressure 10kPa and temperature 298K. Results show that the Mach stem surface which is formed after the shock surface reflection on the upper wall is actually a local overdriven detonation. The side walls in 3D simulations can play an important role in detonation initiation in supersonic combustible mixtures, because they can help realize triple lines collisions and reflections during the initiation process. The width of the channel has an important influence on the strength of side-wall reflections, and under certain condition there might exist a critical width between the front and back sides of the channel for the successful initiation. Both the two-dimensional (2D) and the 3D detonations are overdriven and have a constant but different overdrive after their complete initiations. Although the overdrive degree of the 3D detonation is smaller than that of the 2D case, more complex and irregular detonation fronts can be observed in the 3D case compared with the 2D detonation, which is likely because of the propagation of transverse waves and collisions of triple lines in multi-directions in 3D detonations. After the hot jet is shut down, the newly formed 2D Chapman-Jouguet (CJ) detonation has almost the same characteristic parameters with the corresponding 3D case, indicating that the 2D instabilities can be perfectly preserved in 3D simulations. However, the slapping wave reflections on the side walls in the 3D detonation result in the second oscillation along with the main one, which presents stronger instabilities compared with the 2D case. The inherent stronger 3D instabilities is also verified through the quantitative comparison between the 2D and 3D cases where the 3D result always shows stronger fluctuations than the 2D case

Synthesis and Characterization of Carbon Nanospheres Obtained by Hydrothermal Carbonization of Wood-derived and Other Saccharides

Carbon nanospheres were synthesized by hydrothermal carbonization (HTC) of four different carbon sources: xylose, glucose, sucrose, and pine wood derived saccharides. The obtained carbon nanospheres were characterized for particle morphology and size, and surface functional groups. Morphological and structural differences among these saccharides derived HTC carbons were clearly observed. Scanning electron microscopy images of carbon nanospheres from HTC of xylose showed uniform spherical particles with diameters around 80 nm, while carbon nanospheres obtained from glucose, sucrose, and pine-derived saccharides had particle size  in the range of 100-150 nm, 300-400 nm, and 50-100 nm, respectively. Carbon dioxide and carbon monoxide were primary gaseous phase products during the HTC process. In addition, methane, propane, hydrogen, and benzene were detected in the gas phase.Citation: Yan, Q., Li, R., Toghiani, H., Cai, Z., and Zhang, J. (2015). Synthesis and Characterization of Carbon Nanospheres Obtained by Hydrothermal Carbonization of Wood-derived and Other Saccharides. Trends in Renewable Energy, 1(2), 119-128. DOI: 10.17737/tre.2015.1.2.001

Creep and Creep-Recovery Models for Wood Under High Stress Levels

Forty small clear southern pine specimens were loaded under third-point bending to examine creep and creep-recovery behavior for wood under high stress levels. Stress levels of between 69% and 91% of the predicted static strength were applied for 23 h with 1 h allowed for recovery, and the resulting deflection vs. time behavior was studied. The experimental creep and creep-recovery behavior was modeled using modified power law functions. The results indicate that these functions provide the best fit to both primary and secondary experimental data. The empirical models can be used to simulate the viscoelastic behavior of wood under high stress levels. The simulation will provide a useful tool in future studies to examine duration-of-load (DOL) effect, which is one of the more important factors in wood structural design

Three-dimensional simulation of detonation initiation and propagation in supersonic combustible mixtures

Detonation initiation and propagation in supersonic combustible mixtures using a hot jet have been investigated in three-dimensional numerical simulations with the detailed reaction model on Tianhe-2 system. Results indicate that the side walls can help realize the triple lines collisions and triple lines reflections, which play an important role in the detonation initiation. There should exists a critical width between the front and back sides of the three-dimensional channel for the successful initiation, which is totally different from that of two-dimensional cases. When the width exceeds the critical value, there will be not the effective reflections of the bow shock surface on the side walls, hence resulting in the failure of detonation initiation. For the detonation propagation, none of the standard detonation modes(rectangular mode, diagonal mode and spinning mode) is observed in the three-dimensional case. The initiated detonation is actually in an overdriven state because of the presence of the hot jet in the supersonic flow field, thus resulting in more complex detonation fronts than that in the CJ detonation. Because of both directions of three-dimensional detonation development than that of the two-dimensional case where the transverse waves propagation and the collisions of triple points can be realized only in one direction, the detonation fronts in three-dimensional simulation shows significantly larger irregularities and variations