Moisture movement and thickness swelling in oriented strandboard. Part 2: Analysis using a nuclear magnetic resonance imaging body scanner

The previous paper in this series demonstrates the use of a nuclear magnetic resonance (NMR) micro-imaging system to observe the movement of liquid water through small specimens (11 × 16 mm² cross-section) of oriented strandboard (OSB) and solid wood. In the present paper, a NMR body scanner is utilized to obtain images of moisture penetration into ASTM D 1037–99 standard sized (152 × 152 mm²) thickness swelling specimens at different intervals during water soaking. As with the micro-imaging study, silicone was applied to the surfaces and edges of some of the specimens in order to observe the directional characteristics of moisture movement through OSB. Specimens with commercially applied edge sealant were also included in the study in order to observe the effectiveness of the sealant of reducing moisture penetration and thickness swelling. The presence of voids and areas of low density were shown to contribute significantly to moisture penetration into the specimens.     

Prediction of oriented strand board properties from mat formation and compression operating conditions. Part 2: MOE prediction and process optimization

A model to predict the bending modulus of elasticity (MOE) of oriented strand board (OSB) panels produced by batch processing is presented. The approach developed herein is unique in its comprehensiveness since the MOE is determined from information on the panel structure, temperature and moisture profiles and vertical density profiles obtained from the mat formation and compression models presented in Part 1. Comparison of predicted MOE values with those measured from 24 commercially produced panels shows good agreement considering some of the uncertainties involved. Simulations show that the MOE can be increased by any of the following changes: reduced fines content, increased panel density, better flake alignment in each of the three layers within a panel, increased flake length and a larger difference between the density of the face and core layers. The model was also used in a genetic algorithm to carry out an optimization study of batch OSB manufacturing. This analysis showed that by combining the appropriate reduction in the amount of flakes used, increase in fines content, improvement in flake alignment within each of the face and core layers and shortening of the batch time, a significant theoretical profit increase from the base case scenario can be obtained.     

Effect of mat structure on modulus of elasticity of oriented strandboard

A model to predict bending stiffness of oriented strandboard (OSB) was tested with pilot plant experimental data. The experimental procedure developed in this study is unique in that it allows the model to be tested for extensive vertical configurations of strand angle distribution. After validation, the model was used to simulate a typical three-layer cross-oriented OSB panel with a vertical density profile and strand angle distribution measured on industrial panels. Analysis of the simulated vertical distribution of modulus of elasticity (MOE) indicated that the layers near the panel surfaces contributed much more to the effective parallel panel MOE than those close to the panel thickness center, with 80% of parallel MOE coming from the top 41% of weight and 32% of thickness. The effectiveness of methods to increase parallel bending stiffness through improving mat structure was evaluated. Increasing face/core weight ratio from 54/46 to 66/34 resulted in a 3.7% increase in simulated parallel MOE. Alignment of strands in face layers was identified having a greater potential to increase parallel MOE. Simulations with three improved strand angle distributions showed gains of 5.7, 12.0 and 19.8% in parallel MOE compared with a typical strand angle distribution of industrial OSB panels.     

Weed emergence as influenced by soil moisture and air temperature

Emergence of weed seedlings depends on soil environmental conditions; mainly temperature and moisture, with the latter being fundamental and particularly important in environments which are characterised by irregular amounts and distribution of rainfall throughout the year. Thus, this study looks at the influence of soil moisture and air temperature on the emergence of weed seedlings. The experiment was carried out under controlled environmental conditions, using rings filled with samples of undisturbed topsoil (0–2.5 cm and 0–5 cm deep) of a Luvisol. There were four moisture levels that were maintained constant, with several repetitions (16–20). The results indicate that the maximum population density of weed plants was obtained with soil moisture near field capacity. With regard to the depth of the soil containing the seeds which contributed towards optimising population density, it was noted that the first 2–3 cm of undisturbed soil were critical for maximising the population. The emergence of seedlings was modelled using data from the 5 cm topsoil with soil moisture close to field capacity. This model indicates that a mean daily temperature sum of 446°C, which under Mediterranean autumn conditions represent a period of approximately one month, is needed, in order to obtain 80% of potential autumn-winter plant density, relative to the observed potential.     

Effect of two relative humidity environments on the performance properties of MDF, OSB and chipboard

The static strength, stiffness and fatigue life of MDF, OSB and chipboard have been measured in a 65%RH environment and a 85%RH environment. Chipboard is commonly utilised as a flooring material and OSB is also used in structural applications, for example floor decking and webs of I-beams. The mean static strengths of MDF, OSB and chipboard at 65%RH were 47.9 MPa, 27.9 MPa and 21.0Mpa, respectively, compared with 34.59 MPa, 21.70 MPa and 10.61 MPa at 85%RH. However, MDF has mostly been used in non-structural applications, such as furniture, so its resistance to fatigue loads as a structural panel is of considerable interest. In a 65%RH environment dynamic modulus values showed that whilst MDF and chipboard exhibit similar stiffness values (4 GPa), OSB is approximately 50% stiffer. However, at 85%RH MDF was the stiffest of the three materials, followed by OSB and chipboard. The fatigue life performance of all three panel products was markedly lower at 85%RH compared with 65%RH. Overall, the high RH environment had a noticeably detrimental effect on the MOE (modulus of elasticity), MOR (modulus of rupture) and fatigue lives of OSB and chipboard. This is attributed to these panels retaining more of the original characteristics of the original wood, i.e. larger particle sizes (flakes/chips) compared with the homogeneous fibrous composition of MDF. Received 5 November 1999     

Modelling of vertical density profile of particleboard,manufactured from hardwood sawmill residue

Abstract

Particleboards are generally made in three layers using softwood as the major raw material. Limitation on natural wood resources and concerns about the carbon footprint of products has created a significant interest in environmentally friendly or ‘green’ building materials. Hardwood sawmill residue, which has been disposed as solid waste, was investigated by authors as the main raw material for producing particleboard at RMIT University, Australia. Physical and mechanical properties of final particleboard were measured and analysed against original materials and process variables. The density of a particleboard along its thickness direction is not uniform, and is called the vertical density profile (VDP) which is dependent upon processing parameters. The VDP influences particleboard properties including flexural strength and its dimensional stability and fastening capacity. It is important to influence the formation of the VDP, altering processing variables, to achieve optimum particleboard properties. This paper presents an attempt to develop a model to predict the formation of the VDP of hardwood residue particleboard compared to processing parameters, using the theory of experimental design. The advantages of such a model in optimising particleboard properties are also discussed.     

Appropriate density of water and soil conservation of Pinus tabulaeformis and Robinia pseudoacacia forests in loess area, North China

In this paper, based on a long-term monitoring of water cycle in the water and soil conservation forest stands of Pinus tabulaeformis and Robinia pseudoacacia, the soil moisture deficit is calculated. Following the principles of runoff-collecting forestry and applying the forest structure investigation results, the authors developed a formula to calculate appropriate density for forests on the basis of different diameters at breast height (DBH). Using this method to manage forests, the natural water requirement of forests can be met and soil drought can be avoided. In addition, with long-term monitoring of soil moisture in stands, the authors also give an appropriate managing density specifically for the water and soil conservation forests of P. tabulaeformis and R. pseudoacacia in the loess area which is according to soil moisture content, or with the lowest soil moisture content and invalid moisture frequency as the indexes. __________ Translated from Science of Water and Soil Conservation, 2007, 5(2): 55–59 [译自: 中国水土保持科学]     

The relationship between the arrangement of wood strands at the surface of OSB and the modulus of rupture determined by image analysis

The objective of this paper is to investigate the relationship between the arrangement of wood strands at the surface of oriented strand board (OSB) and the modulus of rupture (MOR) determined by applying the technique of image analysis (IA). Fiber orientation was measured manually. In addition a CCD (charge coupled device) digital camera was used to automatically measure the fiber orientation at the surface of OSB. The total number of OSB samples evaluated was equal to 55, but variation in density was small and the coefficient of variation was only 4%. In contrast, the variation in MOR is wide and the coefficient of variation is 17%. Thus, the variation in density of OSB does not reflect variations in MOR. The relationship between the MOR and the average angle of fiber orientation resulted in a weak negative correlation (r=−0.44) as might be expected, as better axial orientation should improve MOR. The average strand area gave no correlation with MOR. Clearly, large strands which should enhance MOR may be heavily disoriented, whereas small strands which have less influence on the MOR might be well oriented. Hence no correlation between MOR and average strand area is observed. The prediction of MOR by using a multiple linear regression equation including density and fiber orientation factors is only moderately successful. Hence another factor must be identified to predict MOR accurately. The CCD camera measures fiber orientation at the OSB surface effectively. Received 29 March 1999     

Effect of two relative humidity environments on the performance properties of MDF, OSB and chipboard.

The fatigue and creep performance of MDF, OSB and chipboard have been examined in two environments, namely 65%RH (standard environment) and 85%RH (high humidity). Parallel fatigue and creep tests have been performed in four-point bending on the three wood-based panel products in the two environments. The constant 65%RH environment is service class 1 and the constant 85% RH environment is indicative of a service class 2 environment as detailed in Eurocode 5. The non-interruptive technique of stress-strain hysteresis loop capture has been utilised to follow property changes of the fatigue samples during cyclic loading at a stress ratio of R equal to 0.1. Loop parameters such as loop area, dynamic modulus, and fatigue modulus have been used to characterise the response of these materials to fatigue loads in the two environments. Creep microstrains for the creep samples were recorded in parallel with the fatigue parameters. Fatigue and creep results at 85%RH were more variable than those reported at 65%RH for MDF, OSB and chipboard. In general, at R=0.1 and 85%RH, fatigue and creep microstrains were higher, dynamic stiffnesses were lower and hysteresis loop areas were higher than corresponding properties measured at 65%RH. MDF and chipboard were less moisture tolerant than OSB, this is reflected in the large changes in fatigue and creep parameters.     

Predicting oven-dry density of Sugi (Cryptomeria japonica) using near infrared (NIR) spectroscopy and its effect on performance of wood moisture meter

We propose a non-destructive method to predict the oven-dry density of Sugi (Cryptomeria japonica D. Don) using near infrared (NIR) spectroscopy so as to calibrate a commercial moisture meter. A prediction model for oven-dry density was developed using NIR spectra obtained from Sugi samples with a known density. The density of air-dried Sugi boards was predicted with the developed model. Then, the moisture content (MC) of the boards was measured by a hand-held capacitance-type and an in-line microwave moisture meters. For each board, the moisture meters were calibrated by the predicted density. The predicted density was correlated with the measured one with an R ² of 0.81 and a standard error of prediction (SEP) of 15.3 kg/m³ within the measured density of 279.2–436.4 kg/m³, indicating that the developed model was applicable for predicting oven-dry density of Sugi. The MC readings of both moisture meters showed a good correlation with the oven-dry MC that ranged from 12.1 to 28.9 %. For both moisture meters, the density calibration with the NIR-predicted density gave a higher R ² and a lower SEP than with the conventional calibration with the mean density. These results demonstrate that the present density calibration using NIR spectroscopy could improve the performance of the moisture meters for the air-dried Sugi boards with varying densities.     

A new density model of Cryptomeria fortunei plantation

According to the volume increase model of an average individual tree in a plant population and the theory of invariable final output, we put forward a new density model of plant population: V ^β=AN ^β + B. Here N means the stand density and V stands for average individual tree volume; A, B and gb are parameters that change with growth stage. Using the density variation of standard plots of Cryptromeria fortunei plantation to verify the new model, it turns out that this model can well simulate the population density effect law of C. fortunei plantation, and it is markedly better and shows higher accuracy than the commonly used reciprocal model of density effect and secondary-effect model. Let β=1, we can obtain the reciprocal model of density effect, which means the reciprocal model of density effect is only a special case of this new model. __________ Translated from Journal of Fujian College of Forestry, 2005, 25(3) [译自: 福建林学院学报, 2005, 25(3)]     

中国与日本建筑结构用定向刨花板标准对比研究

近年来我国定向刨花板（OSB）产能逐年增加，目前主要应用于家具制造与装修，而在建筑结构中应用相对较少；为了实现我国碳达峰、碳中和目标，随着村镇装配式建筑的发展，建筑结构用OSB使用量必将大幅上升，主要用作木结构和轻钢建筑的墙面板、楼面板和屋面板等结构用覆面板。1987年日本就制定了日本农林标准（JAS）《構造用パネル》（《结构用人造板》，最新版JAS 0360:2019），作为结构用OSB产品质量认证和检测的主要依据，而我国目前没有专用的结构用OSB产品标准。与结构用OSB 日本农林标准比较，我国行业标准LY/T 1580-2010《定向刨花板》中规定的承载型板材在指标要求、试件尺寸和数量、试验方法、抽样方案以及产品合格判定方法等方面存在较大差异。通过对比中日标准技术规定的异同，以期为OSB在我国建筑结构领域使用的规范化与标准化提供参考。鉴于钉连接性能对建筑结构的抗震性能影响显著，建议在我国标准修订中增加该项指标规定。     

Thermal degradation of bending strength of plywood and oriented strand board: a kinetics approach

The construction industry has relied heavily on wood and wood-based composites, such as oriented strand board (OSB) and plywood for timber frame construction. Therefore, it is highly imperative to categorize the response of wood-based composites when exposed to elevated temperatures for a sustained period of time. The essence of fire-resistant structural design is to ensure that structural integrity be maintained during and after the fire, prevent collapse and maintain means of egress. Another aspect is to assess post-fire structural integrity and residual strength of existing structure. The objective of this project was (a) to study the effect of exposure time on bending strength (MOR) of OSB and plywood at elevated temperatures, (b) to interpret any relationships between different temperature and time of exposure using a kinetics model for thermal degradation of strength, and (c) to develop a master curve representing temporal behavior of OSB and plywood at a reference temperature. As much as 1,152 samples were tested in static bending as a function of exposure time and several temperatures. Strength (MOR) of both OSB and plywood decreased as a function of temperature and exposure time. These results were fit to a simple kinetics model, based on the assumption of degradation kinetics following an Arrhenius activation energy model. The apparent activation energies for thermal degradation of strength were 54.1 kJ/mol for OSB and 62.8 kJ/mol for plywood. Furthermore, using the kinetics analysis along with time–temperature superposition, a master curve was generated at a reference temperature of 150°C which predicts degradation of strength with time on exposure at that reference temperature. The master curves show that although plywood has a higher initial strength, OSB performs better in terms of strength degradation after exposure to elevated temperature.     

Inter-crown versus under-crown area: contribution of local configuration of trees to variation in topsoil morphology, pH and moisture in Abies alba Mill. forests

This investigation of three Abies alba stands differing in stem density (338–715 per ha) and vertical structure (one-storeyed or multi-layered) explored the relations between distance from neighbouring tree stems and local canopy openness and selected topsoil properties. The null hypothesis was that in relatively densely stocked forests of close–random stem distribution topsoil morphology, pH and moisture do not differ in inter-crown and under-crown patches. In three plots 1.1 ha in area, soil samples were taken in a square grid 5.0 × 5.0 m and analysed using semivariogram estimation and spatial autocorrelation. The local configuration of trees around the sampled locations was characterised using hemispheral photography and a local stand density index based on tree locations and diameters. The largest portion of the total variation in the soil variables analysed (68–100%) was attributable to small-scale variation in scales <5 m. In all stands, irrespective of density and vertical structure, local stand density/canopy openness correlated positively/negatively with ectohumus layer thickness but negatively/positively with upper soil pH and moisture. Variation in the local configuration of trees explained up to 17% of the total variation in organic horizon thickness, up to 22–29% in topsoil pH (depending on the horizon) and up to 19–27% in topsoil moisture. The results indicate that even in stands of random tree patterning, stem neighbourhood and small-scale variation in canopy density may contribute significantly to topsoil heterogeneity and potentially affect the functioning and structure of forest floor vegetation.     

Predicting moisture content and density distribution of Scots pine by microwave scanning of sawn timber

This study was carried out to investigate the possibility of calibrating a prediction model for the moisture content and density distribution of Scots pine (Pinus sylvestris) using microwave sensors. The material was initially of green moisture content and was thereafter dried in several steps to zero moisture content. At each step, all the pieces were weighed, scanned with a microwave sensor (Satimo 9,4GHz), and computed tomography (CT)-scanned with a medical CT scanner (Siemens Somatom AR.T.). The output variables from the microwave sensor were used as predictors, and CT images that correlated with known moisture content were used as response variables. Multivariate models to predict average moisture content and density were calibrated using the partial least squares (PLS) regression. The models for average moisture content and density were applied at the pixel level, and the distribution was visualized. The results show that it is possible to predict both moisture content distribution and density distribution with high accuracy using microwave sensors.     

Influence of specimen size during accelerated weathering of wood-based structural panels

ABSTRACT

Wood structural panels are commonly subjected to short-term accelerated weathering (AW) procedures to determine relative moisture durability for quality control and product development purposes. The panel edges contribute heavily to moisture uptake since edges represent the least resistant pathway for moisture intrusion. In full-size panels, the edge area to total surface area ratio is small, and moisture intrusion is primarily limited to panel faces. When small specimens are used, such as those in AW procedures, the ratio of edge area to total surface area increases and moisture intrusion at the edges may dominate, which is referred to as the edge effect. The purpose of this study was to determine if physical and mechanical properties of oriented strand board (OSB) and plywood after AW are influenced by specimen size. Specimen width was varied while thickness and length remained constant to understand if edge effects were present in small specimens with different edge area to total surface area ratios. Three AW procedures were evaluated to determine if the effect of specimen size depends on weathering method. No clear effect of specimen size on physical and mechanical properties of either composite type was found. Differences in flexural properties between specimen widths were observed for unweathered OSB, but similar property retention between specimen widths after AW indicated the same trend as the unweathered control. Plywood results were influenced by natural defects, resulting in high variability and absence of statistically significant differences. Lateral nail resistance connection properties of both OSB and plywood were highly variable for all treatment groups and were unaffected by weathering.     

Moisture-induced stresses in engineered wood flooring with OSB substrate

Engineered wood flooring (EWF) is a multilayer composite flooring product. The cross layered structure is designed to give good dimensional stability to the EWF under changing environmental conditions. However, during winter season in North America, the indoor relative humidity could decrease dramatically and generate an important cupping deformation. The main objective of this study was to characterize the interlaminar stresses (σ ₃₃, σ ₁₃ and σ ₂₃) distribution at free-edges in EWF made with an OSB substrate. A three-dimensional (3D) finite element model was used to predict the cupping deformation and to characterize stresses developed in the EWF. The finite element model is based on an unsteady-state moisture transfer equation, a mechanical equilibrium equation and an elastic constitutive law. The physical and mechanical properties of OSB substrate were experimentally determined as a function of the density and moisture content. The simulated EWF deformations were compared against the laboratory observations. For both simulation and experimental results, the cupping deformation of EWF was induced by varying the ambient relative humidity from 50 to 20% at 20°C. A good agreement has been found between the numerical and experimental EWF cupping deformation. The stress distribution fields generated by the model correspond to the delaminations observed on the OSB substrate in the climate room. Delamination in EWF can occur principally under the action of the tension stress or a combination of tension and shear stresses. Finally, simulated results show that the levels of interlaminar stresses are maximal near the free-edges of EWF strips.     

Vessel size and number are contributors to define wood density in cork oak

Cork oak (Quercus suber L.) has a dense wood that allows high-quality uses. In the present work, we study the influence of vessel characteristics, measured through image analysis and optical microscopy, on wood density, measured using X-ray microdensitometry, on 40-year-old trees. Vessel area increases with cambial age (5403–33064 μm²), while wood density decreases (1.229–0.836 g/cm³). The number of vessels is relatively constant at 6 vessels/mm², while vessel proportion in cross-section increases from 3.3% near the pith to 20.5% near the bark. In growth rings closest to the pith, with high wood density and low vessel area, the relationship between the two variables is linear (R ² = −32.1%, P < 0.01) but with increasing tree age and vessel size, the wood density remains rather constant, suggesting that decreases in density might compromise mechanical support of the tree at a stage when the increase in cross-sectional area alone might not provide mechanical stability. Other anatomical characteristics not considered in this study, like large xylem rays that increase with cambial age, may be responsible for the constant density.     

Predicting moisture content and density distribution of Scots pine by microwave scanning of sawn timber II: evaluation of models generated on a pixel level

The purpose of this study was to use images from a microwave sensor on a pixel level for simultaneous prediction of moisture content and density of wood. The microwave sensor functions as a line-scan camera with a pixel size of 8mm. Boards of Scots pine (Pinus sylvestris), 25 and 50mm thick, were scanned at three different moisture contents. Dry density and moisture content for each pixel were calculated from measurements with a computed tomography scanner. It was possible to create models for prediction of density on a pixel level. Models for prediction of moisture content had to be based on average values over homogeneous regions. Accuracy will be improved if it is possible to make a classification of knots, heartwood, sapwood, etc., and calibrate different models for different types of wood. The limitations of the sensor used are high noise in amplitude measurements and the restriction to one period for phase measurements.     

Moisture movement and thickness swelling in oriented strandboard,part 1. Analysis using nuclear magnetic resonance microimaging

A procedure was developed to observe the water absorption characteristics of small specimens of oriented strandboard (OSB) and solid wood in a nuclear magnetic resonance (NMR) microimaging facility. The procedure allowed a specimen to be surrounded in water while remaining in a fixed position within the imaging coil, after which the water could be removed and the specimen immediately imaged. This technique permitted images of the specimen to be taken after a number of different periods of water soak without having to remove and replace the specimen, thus easily maintaining the same image location. Both the distribution of free water and its movement as a function of time were observed using this technique. Inter-strand voids within OSB were shown to be the main route for moisture movement through a specimen of this type. The influence of the inherent anisotropy of OSB on moisture movement was investigated by sealing selected surfaces of a specimen with silicone to observe moisture absorption in predetermined directions.