GRIDCORE TM (FPL Spaceboard) is a three-dimensional, pulpmolded sandwich panel made by depositing... more GRIDCORE TM (FPL Spaceboard) is a three-dimensional, pulpmolded sandwich panel made by depositing and densifying a pulp slurry on a specifically designed resilient mold. Unlike low density pulp-molded products, GRIDCORE TM panels can be highly densified to impart significant mechanical properties. This paper describes our initial efforts at producing GRIDCORE TM panels from blends of old corrugated containers (OCC), old newsprint (ONP), and kenaf. The panels were tested for edge crush strength, flat crush strength, bending strength, and dimensional stability. The results indicate that desirable mechanical properties can be achieved from all panel compositions. BACKGROUND
This article was written and prepared by U.S. Government employees on official time, and it is th... more This article was written and prepared by U.S. Government employees on official time, and it is therefore in the public domain and not subject to copyright. Introduction
Wet-formed particleboard panels were made using cellulose nanofibrils (CNF) as the bonding materi... more Wet-formed particleboard panels were made using cellulose nanofibrils (CNF) as the bonding material. The effects of panel density, CNF addition ratio, particle size, and pressing method on the nail and face screw withdrawal strength, water absorption (WA), and thickness swelling (TS) were investigated. The nail and face screw withdrawal strength increased with an increased panel density and CNF addition ratio. Mixed-size particles were favorable for better face screw withdrawal strength. The WA decreased while TS increased with increased panel density. The WA decreased with increased CNF addition ratio. The effect of CNF addition ratio on the TS was influenced by an interaction effect of the particle size, density, and pressing method. Smaller wood particles and the constant thickness (CT) pressing method were better for both WA and TS performance. All of the high- and medium-density panels failed to satisfy the standard requirements for face screw withdrawal strength. For low-densi...
Ability to determine stresses in loaded, perforated cellulosic-manure composites from recorded te... more Ability to determine stresses in loaded, perforated cellulosic-manure composites from recorded temperature information was demonstrated. Being able to stress analyze such green materials addresses several societal issues. These include providing engineering members fabricated from materials that are suitable for developed and developing nations, relieving a troubling by-product of agricultural regions and reducing demands on our landfills. Most engineering applications of these materials necessitate knowing their structural integrity eg capability to evaluate stresses.
In this study, the effects of cellulose nanofibrils (CNFs) ratio, press program, particle size, a... more In this study, the effects of cellulose nanofibrils (CNFs) ratio, press program, particle size, and density on the vertical density profile (VDP) and internal bond (IB) strength of the wet-formed particleboard were investigated. Results revealed that the VDP was significantly influenced by the press program. Pressing using a constant pressure (CP) press program produced panels with flat-shaped profile. Panels made from a constant thickness (CT) press program produced U-shaped profile. The CNF ratio and density also influenced the VDP especially for the CT panels. As the CNF ratio increased, there were noticeable increases in face density, while the core density slowly increased. The CT panels had the lowest core density compared with the CP counterparts, thus significantly lowering the IB. The IB of CP panels increased with the increase of CNF ratio, but the trend for CT panels was different. For the 10% CNF ratio, the IB increased as the core density increased. For the 15% and 20% ...
A key path towards the commercialization of cellulose nanomaterials is to target large-volume app... more A key path towards the commercialization of cellulose nanomaterials is to target large-volume applications in commodity products where a successful market introduction could potentially mobilize orchestrated efforts to revitalize the forest products industry. At the Laboratory of Renewable Nanomaterials we have introduced the concept of using cellulose nanofibrils (CNF) as binder in conventional wood based compressed panels. Binder applications take advantage of impressive hydrogen bonding capacity of CNF and have many other uses. In this presentation, we will present our findings in wet-formed particleboard bonded with cellulose nanofibrils (CNF). In an effort to lower the production cost, we have also shown that lingo-cellulose nanofibrils can be produced directly from wood and can be used as binder in the formulation of traditional fiberboard panels. Thermomechanical pulp (TMP) produced using atmospheric refining was ground to isolate lignocellulose nanofibrils (LCNF). The effect...
This paper presented construction and strain distributions for lightweight wood-fiber-based struc... more This paper presented construction and strain distributions for lightweight wood-fiber-based structural panels with tri-grid core made from phenolic impregnated laminated paper composites under bending. A new fastening configuration of slots in the faces and tabs on the core was applied to the face/core interfaces of the sandwich panel in addition to epoxy resin. Both normal strain gages and shear strain gages were attached on these panels to analyze inside strain distributions by third point load bending test. The purpose of the bending test was to investigate the various strain distributions of panels with different face/ core configurations that identified the critical failure modes for future design. In this research, four panels with different configurations were constructed to analyze the influence of strain distributions for bending behavior. Either maximum localized normal strain or shear strain were used to judge failures and associated failure modes through observation. Test results of strain distribution showed normal strain was primarily carried by both top and bottom faces. As bending load increased, compression buckling occurred on the top surface of some panels with thinner faces. Face thickness and stiffness significantly affected the strength of the panel as evident by nonlinear strain behavior. Meanwhile, the shear strain was primarily taken by the ribs in the structural core, and shear failure always occurred in the longitudinal linear ribs of core with thicker faces. The shear strain in the cross ribs was approximately half that of the longitudinal linear ribs in the same section of shear zone, which was consistent with the geometric formula. The problem of panel imperfections resulting in either face compression buckling or rib shear buckling could be overcome by further design optimization, and the analytical modeling for bending design and evaluation was presented.
Wet-formed particleboard bonded with cellulose nanofibrils (CNF) was prepared in this work. The e... more Wet-formed particleboard bonded with cellulose nanofibrils (CNF) was prepared in this work. The effects of density, CNF addition ratio, pressing method, and particle size on the bending strength were evaluated. The results showed that density had the most important effect on the modulus of elasticity (MOE), while the CNF addition ratio had the most important effect on the modulus of rupture (MOR). For panels with low density (< 640 kg/m 3), the MOE and MOR did not change much with the configuration changes between particle size and pressing method. This was due to the synergistic effect of incomplete compression and poor bonding in the core area using a constant thickness (CT) pressing method, and lower face density and higher core density using a constant pressure (CP) pressing method. For panels with medium density (640 kg/m 3 to 800 kg/m 3), the combination of larger particles, higher CNF addition ratio, and CT pressing method contributed to the highest bending strength. Further increase to high density (> 800 kg/m 3), the pressing method's effect was more important, compared to panels with low and medium densities. With increased density and CNF addition ratio, panels were able to meet lowdensity and some medium-density standard MOE and MOR requirements.
Composites Part A: Applied Science and Manufacturing, 2016
This paper presents static and fatigue bending behavior for a wood-based structural panel having ... more This paper presents static and fatigue bending behavior for a wood-based structural panel having a slot and tab (S/T) construction technique. Comparisons were made with similarly fabricated panels without the S/T construction technique. Experimental results showed that both types of panels had similar bending properties in the static tests. However, the panels with S/T construction had better fatigue results. The failure modes were different for the two fabrication techniques. The panels without S/T
This paper presents a simplified analytical model and balanced design approach for modeling light... more This paper presents a simplified analytical model and balanced design approach for modeling lightweight 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.
This paper presents experimental results of both quasi-static compression and low-velocity impact... more This paper presents experimental results of both quasi-static compression and low-velocity impact behavior for tri-axial bio-composite structural panels using a spherical load head. Panels were made having different core and face configurations. The results showed that panels made having either carbon fiber fabric composite faces or a foam-filled core had significantly improved impact and compressive performance over panels without either. Different localized impact responses were observed based on the location of the compression or impact relative to the tri-axial structural core; the core with a smaller structural element had better impact performance. Furthermore, during the early contact phase for both quasi-static compression and low-velocity impact tests, the panels with the same configuration had similar load-displacement responses. The experimental results show basic compression data could be used for the future design and optimization of tri-axial bio-composite structural p...
This paper presents an analysis of 3-dimensional engineered structural panels (3DESP) made from w... more This paper presents an analysis of 3-dimensional engineered structural panels (3DESP) made from woodfiber-based laminated paper composites. Since the existing models for calculating the mechanical behavior of core configurations within sandwich panels are very complex, a new simplified orthogonal model (SOM) using an equivalent element has been developed. This model considers both linear and nonlinear geometrical effects when used to analyze the mechanical properties of 3DESP by transforming repeated elements from a tri-axial ribbed core for bending. Two different conditions were studied in comparison with finite element method (FEM) and I-beam equation. The results showed the SOM was consistent with FEM and the experimental result and were more accurate than the I-beam equation. The SOM considering nonlinear geometric deformation needed more computational effort and was found to match well with a FEM model and had slightly better accuracy compared with the linear SOM. Compared with FEM, the parameters in the linear SOM were easier to modify for predicting point-by-point bending performance. However, while the FEM can provide advanced characteristics of the 3DESP such as strain distribution, the linear SOM provided acceptable deformation accuracy and is proposed for preliminary design with multiple parameters. FEM should be applied for advanced analyses.
Stress and strain concentrations and in-plane and out-of-plane stress constraint factors associat... more Stress and strain concentrations and in-plane and out-of-plane stress constraint factors associated with a circular hole in thick, loaded orthotropic composite plates are determined by three-dimensional finite element method. The plate has essentially infinite in-plane geometry but finite thickness. Results for Sitka spruce wood are emphasized, although some for carbon-epoxy composites are included. While some results are similar to those for isotropy, there are significant consequences due to material orthotropy. Maximum stress and strain concentration factors occur at midplane for thin plates but closer to the external traction-free surfaces for thick plates. These factors decrease as the plate surface is approached and reach lower values unrepresentative of the maximum values. Differences between the midplane and/or maximum and surface stress or strain concentration factors in Sitka spruce, range from 8% if the wood grain is parallel to the vertically applied load to 15% when the grain is perpendicular to the load. These values exceed those typically reported for isotropic materials. Stress and strain concentration factors tend to differ in magnitude from each other. The combination of high local stresses and directional strength dependency of orthotropic materials can be particularly important. That maximum stress and/or strain concentrations in thick plates occur on other than the external plate surfaces where they are most readily measured is technically significant. The E 11 =E 22 ratio in Sitka Spruce exceeds that in the carbon composite by 60%. However, when loading parallel to the strong/stiff directions, the plane-stress tensile stress concentration factors of the two materials are comparable to each other.
The static and fatigue bending behavior of wood-fiber-based tri-axial engineered sandwich composi... more The static and fatigue bending behavior of wood-fiber-based tri-axial engineered sandwich composite panels (ESCP) has been investigated by four-point bending tests. Fatigue panels and weakened panels (wESCP) with an initial interface defect were manufactured for the fatigue tests. Stress σ vs. number of cycles curves (S-N) were recorded under the different stress levels. The primary failure mode in the fatigue tests was observed in the shear zone (epoxy debonding), which was different from face failure in the pure bending zone for the static bending test. For residual bending (RB) test, epoxy debonding failure occurred between the pure bending zone and shear zone. Macro cracks along the core/face interface developed as the number of cycles increased during the fatigue life. The crack propagation or damage for the panels submitted to fatigue test can be described as a three-stage damage process of first non-linear portion, followed by linear damage accumulation, and lastly non-linear...
As a part of the National Fire Plan, the USDA Forest Service is conducting research to reduce the... more As a part of the National Fire Plan, the USDA Forest Service is conducting research to reduce the severity of forest fires through effective utilization of low-or no-value logging residues and forest thinnings. This report explores the effect of pro cessing on the physical properties of the fibrous material and flat fiberboard panels made from small-diameter lodgepole pine treetops processed with the bark. Delimbed treetops were chipped and fiberized with water using commercial equipment, di gested with hot water and/or small amounts of chemical additives, refined in a disk refiner, and hot-pressed to make flat panels. To observe only the effects of water and additives on fiber bonding, adhesive resin was not used. We evaluated the effects of processing variables (digester temperature, refining level, and sodium hydroxide content) on fiber length, freeness, fines content, and shive content. Fiber quality was related to mechanical properties of the flat panels. The mechanical properties of the resinfree fiberboard surpassed the minimum standards for commercial hardboard. We conclude that small-diameter lodgepole pine treetops with bark are well-suited for the production of structural boards. This research is part of a larger program for developing three-dimensional geometries for engineered fiberboard products. The forest floor of many National and private forests in the Western United States is covered by large amounts of densely packed small-diameter material and dry residue from harvesting or thinning operations (Fig. 1). This material has accumulated because it has low, no, or even negative value for products given current processing or utilization technology. The dry or semiarid conditions in the West cause the material to decompose slowly, increasing the fuel load for forest fires. After decades of effective forest fire prevention and an accu mulation of forest biomass, forest fires have become an in creasing hazard (USDA Forest Serv. 2004). The private sector could be an outlet for this material and could reduce the fuel load if there were economical processes that could handle this material and produce value-added products. This paper discusses the effects of processing variables on the properties of fiber made from lodgepole pine treetops and the relationship of fiber properties to fiberboard panel prop erties. The goal is to develop a simple and economic means to reduce forest residue into a bondable fibrous material for use in three-dimensional engineered fiberboard structural appli cations.
The anisotropy of wood creates a complex problem requiring that analyses be based on fundamental ... more The anisotropy of wood creates a complex problem requiring that analyses be based on fundamental material properties and characteristics of the wood structure to solve heat transfer problems. A two-dimensional finite element model that evaluates the effective thermal conductivity of a wood cell over the full range of moisture contents and porosities was previously developed, but its dependence on software limits its use. A statistical curve-fit to finite-element results would provide a simplified expres sion of the model's results without the need for software to interpolate values. This paper develops an explicit equation for the values from the finite-element thermal conductivity analysis. The equation is derived from a fundamental equivalent resistive-circuit model for general thermal conductivity problems. Constants were added to the equation to improve the regression-fit for the resistive model. The equation determines thermal conductivity values for the full range of densities and moisture contents. This new equation provides thermal conductivity values for uniform-density wood material using inputs of only oven-dry density and moisture content. An explicit method for determining thermal conductivity of uniform density wood cells has potential uses for many wood applications.
A three-dimensional structural panel, called FPL Spaceboard, was developed at the USDA Forest Pro... more A three-dimensional structural panel, called FPL Spaceboard, was developed at the USDA Forest Products Laboratory. Spaceboard panels have been formed using a variety of fibrous materials using either a wet-or dry-forming process. Geometrically, the panel departs from the traditional two-dimensional flat panel by integrally forming an array of perpendicular ribs and face in one structure. In the literature, significant work has been conducted to model drying of two-dimensional panels, but no known work has been done on such a three-dimensional structure. In order to optimise the drying efficiency and structural performance for this new panel, there is a need to understand the complex drying process that occurs within the panel. This paper is the second of several to discuss the modeling work. The model itself will be presented in a paper to be published. In this paper, internal temperatures, thickness, moisture content, drying rates, and mechanical properties as a function of time ar...
Wood-based composite panels generally are first tested out-of-plane in the primary panel directio... more Wood-based composite panels generally are first tested out-of-plane in the primary panel direction followed by the cross panel direction, but rarely edgewise. While most applications use wood-based composites in the flat-wise orientation and only need the out-of-plane properties, there are construction configurations where edgewise properties are needed for improved design configurations. A square cantilever beam was used to determine the apparent stiffness (EI) and modulus of elasticity (E) differences for 3 wood-based composite panel materials. Specimens were cut along the primary panel direction or machine direction (MD) and perpendicular to the primary direction or cross-machine direction (CD). The square specimens were first non-destructively tested oriented in the normal or out-of-plane position, then rotated 90 degrees to measure edgewise properties. The results for a 20 mm thick medium density fiberboard (MDF) showed that the MD properties were 56% higher than the CD properties. The other two composite materials, 12 mm thick particleboard (PB) and 12 mm thick MDF, were essentially the same in the MD or CD directions. For all the materials, the differences between the out-of-plane and the edgewise loading directions showed higher EI and E between 17 to 61%, respectively. The largest difference was found in the PB composite material properties that were between 42 to 61% higher for the out-of-plane properties. For the 12 and 20 mm thick MDF material, inplane properties were 27 to 33% and 17 to 23% higher, respectively. The cantilever bending method was able to quickly assess the difference using the same specimen.
Fiberboard is a common interior material used both in China and the United States of America. The... more Fiberboard is a common interior material used both in China and the United States of America. The increase in demand for interior materials has raised concerns regarding combustibility of the materials. The pyrolysis characteristics of fiber, phenolic resin (PF), and nano kaolinclay (NK) were investigated using thermogravimetry. The fire performances of samples coated with a mixture of NK and PF were determined using a cone calorimeter. The pyrolysis process of fiber included three phases dependent on chemical composition. The initial temperature of PF pyrolysis was about 100 °C and it stopped at 280°C. The major mass loss of NK was observed between 400 to 600 °C due to the gradual oxolation of the metakaolin. In comparison with fiber board, samples coated with a mixture of NK and PF achieved a better fire performance. The results showed a longer TTI, lower HRR, and THR, and less CO and CO 2 yield, especially from a mixture of NK (90%) and PF (10%). The application of an NK and PF mixture to fiber board as a flame retardant is an effective method for enhancing fire safety and resistance.
Mechanical analysis is presented for new high-strength sandwich panels made from wood-based pheno... more Mechanical analysis is presented for new high-strength sandwich panels made from wood-based phenolic impregnated laminated paper assembled with an interlocking tri-axial ribbed core. Four different panel configurations were tested, including panels with fiberglass fabric bonded to both outside faces with self-expanding urethane foam used to fill the ribbed core. The mechanical behaviors of the sandwich panels were strength tested via flatwise compression, edgewise compression, and third-point load bending. Panels with fiberglass exhibited significantly increased strength and apparent MOE in edgewise compression and bending, but there were no noticeable effects in flatwise compression. The foam provided improved support that resisted both rib buckling and face buckling for both compression and bending tests. Post-failure observation indicated that core buckling dominated the failures for all configurations used. It is believed that using stiffer foam or optimizing the dimension of the core might further improve the mechanical performance of wood-based sandwich panels.
GRIDCORE TM (FPL Spaceboard) is a three-dimensional, pulpmolded sandwich panel made by depositing... more GRIDCORE TM (FPL Spaceboard) is a three-dimensional, pulpmolded sandwich panel made by depositing and densifying a pulp slurry on a specifically designed resilient mold. Unlike low density pulp-molded products, GRIDCORE TM panels can be highly densified to impart significant mechanical properties. This paper describes our initial efforts at producing GRIDCORE TM panels from blends of old corrugated containers (OCC), old newsprint (ONP), and kenaf. The panels were tested for edge crush strength, flat crush strength, bending strength, and dimensional stability. The results indicate that desirable mechanical properties can be achieved from all panel compositions. BACKGROUND
This article was written and prepared by U.S. Government employees on official time, and it is th... more This article was written and prepared by U.S. Government employees on official time, and it is therefore in the public domain and not subject to copyright. Introduction
Wet-formed particleboard panels were made using cellulose nanofibrils (CNF) as the bonding materi... more Wet-formed particleboard panels were made using cellulose nanofibrils (CNF) as the bonding material. The effects of panel density, CNF addition ratio, particle size, and pressing method on the nail and face screw withdrawal strength, water absorption (WA), and thickness swelling (TS) were investigated. The nail and face screw withdrawal strength increased with an increased panel density and CNF addition ratio. Mixed-size particles were favorable for better face screw withdrawal strength. The WA decreased while TS increased with increased panel density. The WA decreased with increased CNF addition ratio. The effect of CNF addition ratio on the TS was influenced by an interaction effect of the particle size, density, and pressing method. Smaller wood particles and the constant thickness (CT) pressing method were better for both WA and TS performance. All of the high- and medium-density panels failed to satisfy the standard requirements for face screw withdrawal strength. For low-densi...
Ability to determine stresses in loaded, perforated cellulosic-manure composites from recorded te... more Ability to determine stresses in loaded, perforated cellulosic-manure composites from recorded temperature information was demonstrated. Being able to stress analyze such green materials addresses several societal issues. These include providing engineering members fabricated from materials that are suitable for developed and developing nations, relieving a troubling by-product of agricultural regions and reducing demands on our landfills. Most engineering applications of these materials necessitate knowing their structural integrity eg capability to evaluate stresses.
In this study, the effects of cellulose nanofibrils (CNFs) ratio, press program, particle size, a... more In this study, the effects of cellulose nanofibrils (CNFs) ratio, press program, particle size, and density on the vertical density profile (VDP) and internal bond (IB) strength of the wet-formed particleboard were investigated. Results revealed that the VDP was significantly influenced by the press program. Pressing using a constant pressure (CP) press program produced panels with flat-shaped profile. Panels made from a constant thickness (CT) press program produced U-shaped profile. The CNF ratio and density also influenced the VDP especially for the CT panels. As the CNF ratio increased, there were noticeable increases in face density, while the core density slowly increased. The CT panels had the lowest core density compared with the CP counterparts, thus significantly lowering the IB. The IB of CP panels increased with the increase of CNF ratio, but the trend for CT panels was different. For the 10% CNF ratio, the IB increased as the core density increased. For the 15% and 20% ...
A key path towards the commercialization of cellulose nanomaterials is to target large-volume app... more A key path towards the commercialization of cellulose nanomaterials is to target large-volume applications in commodity products where a successful market introduction could potentially mobilize orchestrated efforts to revitalize the forest products industry. At the Laboratory of Renewable Nanomaterials we have introduced the concept of using cellulose nanofibrils (CNF) as binder in conventional wood based compressed panels. Binder applications take advantage of impressive hydrogen bonding capacity of CNF and have many other uses. In this presentation, we will present our findings in wet-formed particleboard bonded with cellulose nanofibrils (CNF). In an effort to lower the production cost, we have also shown that lingo-cellulose nanofibrils can be produced directly from wood and can be used as binder in the formulation of traditional fiberboard panels. Thermomechanical pulp (TMP) produced using atmospheric refining was ground to isolate lignocellulose nanofibrils (LCNF). The effect...
This paper presented construction and strain distributions for lightweight wood-fiber-based struc... more This paper presented construction and strain distributions for lightweight wood-fiber-based structural panels with tri-grid core made from phenolic impregnated laminated paper composites under bending. A new fastening configuration of slots in the faces and tabs on the core was applied to the face/core interfaces of the sandwich panel in addition to epoxy resin. Both normal strain gages and shear strain gages were attached on these panels to analyze inside strain distributions by third point load bending test. The purpose of the bending test was to investigate the various strain distributions of panels with different face/ core configurations that identified the critical failure modes for future design. In this research, four panels with different configurations were constructed to analyze the influence of strain distributions for bending behavior. Either maximum localized normal strain or shear strain were used to judge failures and associated failure modes through observation. Test results of strain distribution showed normal strain was primarily carried by both top and bottom faces. As bending load increased, compression buckling occurred on the top surface of some panels with thinner faces. Face thickness and stiffness significantly affected the strength of the panel as evident by nonlinear strain behavior. Meanwhile, the shear strain was primarily taken by the ribs in the structural core, and shear failure always occurred in the longitudinal linear ribs of core with thicker faces. The shear strain in the cross ribs was approximately half that of the longitudinal linear ribs in the same section of shear zone, which was consistent with the geometric formula. The problem of panel imperfections resulting in either face compression buckling or rib shear buckling could be overcome by further design optimization, and the analytical modeling for bending design and evaluation was presented.
Wet-formed particleboard bonded with cellulose nanofibrils (CNF) was prepared in this work. The e... more Wet-formed particleboard bonded with cellulose nanofibrils (CNF) was prepared in this work. The effects of density, CNF addition ratio, pressing method, and particle size on the bending strength were evaluated. The results showed that density had the most important effect on the modulus of elasticity (MOE), while the CNF addition ratio had the most important effect on the modulus of rupture (MOR). For panels with low density (< 640 kg/m 3), the MOE and MOR did not change much with the configuration changes between particle size and pressing method. This was due to the synergistic effect of incomplete compression and poor bonding in the core area using a constant thickness (CT) pressing method, and lower face density and higher core density using a constant pressure (CP) pressing method. For panels with medium density (640 kg/m 3 to 800 kg/m 3), the combination of larger particles, higher CNF addition ratio, and CT pressing method contributed to the highest bending strength. Further increase to high density (> 800 kg/m 3), the pressing method's effect was more important, compared to panels with low and medium densities. With increased density and CNF addition ratio, panels were able to meet lowdensity and some medium-density standard MOE and MOR requirements.
Composites Part A: Applied Science and Manufacturing, 2016
This paper presents static and fatigue bending behavior for a wood-based structural panel having ... more This paper presents static and fatigue bending behavior for a wood-based structural panel having a slot and tab (S/T) construction technique. Comparisons were made with similarly fabricated panels without the S/T construction technique. Experimental results showed that both types of panels had similar bending properties in the static tests. However, the panels with S/T construction had better fatigue results. The failure modes were different for the two fabrication techniques. The panels without S/T
This paper presents a simplified analytical model and balanced design approach for modeling light... more This paper presents a simplified analytical model and balanced design approach for modeling lightweight 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.
This paper presents experimental results of both quasi-static compression and low-velocity impact... more This paper presents experimental results of both quasi-static compression and low-velocity impact behavior for tri-axial bio-composite structural panels using a spherical load head. Panels were made having different core and face configurations. The results showed that panels made having either carbon fiber fabric composite faces or a foam-filled core had significantly improved impact and compressive performance over panels without either. Different localized impact responses were observed based on the location of the compression or impact relative to the tri-axial structural core; the core with a smaller structural element had better impact performance. Furthermore, during the early contact phase for both quasi-static compression and low-velocity impact tests, the panels with the same configuration had similar load-displacement responses. The experimental results show basic compression data could be used for the future design and optimization of tri-axial bio-composite structural p...
This paper presents an analysis of 3-dimensional engineered structural panels (3DESP) made from w... more This paper presents an analysis of 3-dimensional engineered structural panels (3DESP) made from woodfiber-based laminated paper composites. Since the existing models for calculating the mechanical behavior of core configurations within sandwich panels are very complex, a new simplified orthogonal model (SOM) using an equivalent element has been developed. This model considers both linear and nonlinear geometrical effects when used to analyze the mechanical properties of 3DESP by transforming repeated elements from a tri-axial ribbed core for bending. Two different conditions were studied in comparison with finite element method (FEM) and I-beam equation. The results showed the SOM was consistent with FEM and the experimental result and were more accurate than the I-beam equation. The SOM considering nonlinear geometric deformation needed more computational effort and was found to match well with a FEM model and had slightly better accuracy compared with the linear SOM. Compared with FEM, the parameters in the linear SOM were easier to modify for predicting point-by-point bending performance. However, while the FEM can provide advanced characteristics of the 3DESP such as strain distribution, the linear SOM provided acceptable deformation accuracy and is proposed for preliminary design with multiple parameters. FEM should be applied for advanced analyses.
Stress and strain concentrations and in-plane and out-of-plane stress constraint factors associat... more Stress and strain concentrations and in-plane and out-of-plane stress constraint factors associated with a circular hole in thick, loaded orthotropic composite plates are determined by three-dimensional finite element method. The plate has essentially infinite in-plane geometry but finite thickness. Results for Sitka spruce wood are emphasized, although some for carbon-epoxy composites are included. While some results are similar to those for isotropy, there are significant consequences due to material orthotropy. Maximum stress and strain concentration factors occur at midplane for thin plates but closer to the external traction-free surfaces for thick plates. These factors decrease as the plate surface is approached and reach lower values unrepresentative of the maximum values. Differences between the midplane and/or maximum and surface stress or strain concentration factors in Sitka spruce, range from 8% if the wood grain is parallel to the vertically applied load to 15% when the grain is perpendicular to the load. These values exceed those typically reported for isotropic materials. Stress and strain concentration factors tend to differ in magnitude from each other. The combination of high local stresses and directional strength dependency of orthotropic materials can be particularly important. That maximum stress and/or strain concentrations in thick plates occur on other than the external plate surfaces where they are most readily measured is technically significant. The E 11 =E 22 ratio in Sitka Spruce exceeds that in the carbon composite by 60%. However, when loading parallel to the strong/stiff directions, the plane-stress tensile stress concentration factors of the two materials are comparable to each other.
The static and fatigue bending behavior of wood-fiber-based tri-axial engineered sandwich composi... more The static and fatigue bending behavior of wood-fiber-based tri-axial engineered sandwich composite panels (ESCP) has been investigated by four-point bending tests. Fatigue panels and weakened panels (wESCP) with an initial interface defect were manufactured for the fatigue tests. Stress σ vs. number of cycles curves (S-N) were recorded under the different stress levels. The primary failure mode in the fatigue tests was observed in the shear zone (epoxy debonding), which was different from face failure in the pure bending zone for the static bending test. For residual bending (RB) test, epoxy debonding failure occurred between the pure bending zone and shear zone. Macro cracks along the core/face interface developed as the number of cycles increased during the fatigue life. The crack propagation or damage for the panels submitted to fatigue test can be described as a three-stage damage process of first non-linear portion, followed by linear damage accumulation, and lastly non-linear...
As a part of the National Fire Plan, the USDA Forest Service is conducting research to reduce the... more As a part of the National Fire Plan, the USDA Forest Service is conducting research to reduce the severity of forest fires through effective utilization of low-or no-value logging residues and forest thinnings. This report explores the effect of pro cessing on the physical properties of the fibrous material and flat fiberboard panels made from small-diameter lodgepole pine treetops processed with the bark. Delimbed treetops were chipped and fiberized with water using commercial equipment, di gested with hot water and/or small amounts of chemical additives, refined in a disk refiner, and hot-pressed to make flat panels. To observe only the effects of water and additives on fiber bonding, adhesive resin was not used. We evaluated the effects of processing variables (digester temperature, refining level, and sodium hydroxide content) on fiber length, freeness, fines content, and shive content. Fiber quality was related to mechanical properties of the flat panels. The mechanical properties of the resinfree fiberboard surpassed the minimum standards for commercial hardboard. We conclude that small-diameter lodgepole pine treetops with bark are well-suited for the production of structural boards. This research is part of a larger program for developing three-dimensional geometries for engineered fiberboard products. The forest floor of many National and private forests in the Western United States is covered by large amounts of densely packed small-diameter material and dry residue from harvesting or thinning operations (Fig. 1). This material has accumulated because it has low, no, or even negative value for products given current processing or utilization technology. The dry or semiarid conditions in the West cause the material to decompose slowly, increasing the fuel load for forest fires. After decades of effective forest fire prevention and an accu mulation of forest biomass, forest fires have become an in creasing hazard (USDA Forest Serv. 2004). The private sector could be an outlet for this material and could reduce the fuel load if there were economical processes that could handle this material and produce value-added products. This paper discusses the effects of processing variables on the properties of fiber made from lodgepole pine treetops and the relationship of fiber properties to fiberboard panel prop erties. The goal is to develop a simple and economic means to reduce forest residue into a bondable fibrous material for use in three-dimensional engineered fiberboard structural appli cations.
The anisotropy of wood creates a complex problem requiring that analyses be based on fundamental ... more The anisotropy of wood creates a complex problem requiring that analyses be based on fundamental material properties and characteristics of the wood structure to solve heat transfer problems. A two-dimensional finite element model that evaluates the effective thermal conductivity of a wood cell over the full range of moisture contents and porosities was previously developed, but its dependence on software limits its use. A statistical curve-fit to finite-element results would provide a simplified expres sion of the model's results without the need for software to interpolate values. This paper develops an explicit equation for the values from the finite-element thermal conductivity analysis. The equation is derived from a fundamental equivalent resistive-circuit model for general thermal conductivity problems. Constants were added to the equation to improve the regression-fit for the resistive model. The equation determines thermal conductivity values for the full range of densities and moisture contents. This new equation provides thermal conductivity values for uniform-density wood material using inputs of only oven-dry density and moisture content. An explicit method for determining thermal conductivity of uniform density wood cells has potential uses for many wood applications.
A three-dimensional structural panel, called FPL Spaceboard, was developed at the USDA Forest Pro... more A three-dimensional structural panel, called FPL Spaceboard, was developed at the USDA Forest Products Laboratory. Spaceboard panels have been formed using a variety of fibrous materials using either a wet-or dry-forming process. Geometrically, the panel departs from the traditional two-dimensional flat panel by integrally forming an array of perpendicular ribs and face in one structure. In the literature, significant work has been conducted to model drying of two-dimensional panels, but no known work has been done on such a three-dimensional structure. In order to optimise the drying efficiency and structural performance for this new panel, there is a need to understand the complex drying process that occurs within the panel. This paper is the second of several to discuss the modeling work. The model itself will be presented in a paper to be published. In this paper, internal temperatures, thickness, moisture content, drying rates, and mechanical properties as a function of time ar...
Wood-based composite panels generally are first tested out-of-plane in the primary panel directio... more Wood-based composite panels generally are first tested out-of-plane in the primary panel direction followed by the cross panel direction, but rarely edgewise. While most applications use wood-based composites in the flat-wise orientation and only need the out-of-plane properties, there are construction configurations where edgewise properties are needed for improved design configurations. A square cantilever beam was used to determine the apparent stiffness (EI) and modulus of elasticity (E) differences for 3 wood-based composite panel materials. Specimens were cut along the primary panel direction or machine direction (MD) and perpendicular to the primary direction or cross-machine direction (CD). The square specimens were first non-destructively tested oriented in the normal or out-of-plane position, then rotated 90 degrees to measure edgewise properties. The results for a 20 mm thick medium density fiberboard (MDF) showed that the MD properties were 56% higher than the CD properties. The other two composite materials, 12 mm thick particleboard (PB) and 12 mm thick MDF, were essentially the same in the MD or CD directions. For all the materials, the differences between the out-of-plane and the edgewise loading directions showed higher EI and E between 17 to 61%, respectively. The largest difference was found in the PB composite material properties that were between 42 to 61% higher for the out-of-plane properties. For the 12 and 20 mm thick MDF material, inplane properties were 27 to 33% and 17 to 23% higher, respectively. The cantilever bending method was able to quickly assess the difference using the same specimen.
Fiberboard is a common interior material used both in China and the United States of America. The... more Fiberboard is a common interior material used both in China and the United States of America. The increase in demand for interior materials has raised concerns regarding combustibility of the materials. The pyrolysis characteristics of fiber, phenolic resin (PF), and nano kaolinclay (NK) were investigated using thermogravimetry. The fire performances of samples coated with a mixture of NK and PF were determined using a cone calorimeter. The pyrolysis process of fiber included three phases dependent on chemical composition. The initial temperature of PF pyrolysis was about 100 °C and it stopped at 280°C. The major mass loss of NK was observed between 400 to 600 °C due to the gradual oxolation of the metakaolin. In comparison with fiber board, samples coated with a mixture of NK and PF achieved a better fire performance. The results showed a longer TTI, lower HRR, and THR, and less CO and CO 2 yield, especially from a mixture of NK (90%) and PF (10%). The application of an NK and PF mixture to fiber board as a flame retardant is an effective method for enhancing fire safety and resistance.
Mechanical analysis is presented for new high-strength sandwich panels made from wood-based pheno... more Mechanical analysis is presented for new high-strength sandwich panels made from wood-based phenolic impregnated laminated paper assembled with an interlocking tri-axial ribbed core. Four different panel configurations were tested, including panels with fiberglass fabric bonded to both outside faces with self-expanding urethane foam used to fill the ribbed core. The mechanical behaviors of the sandwich panels were strength tested via flatwise compression, edgewise compression, and third-point load bending. Panels with fiberglass exhibited significantly increased strength and apparent MOE in edgewise compression and bending, but there were no noticeable effects in flatwise compression. The foam provided improved support that resisted both rib buckling and face buckling for both compression and bending tests. Post-failure observation indicated that core buckling dominated the failures for all configurations used. It is believed that using stiffer foam or optimizing the dimension of the core might further improve the mechanical performance of wood-based sandwich panels.
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Papers by John Hunt