定向刨花板剪切模量和弹性模量动态测试

【目的】研究定向刨花板(OSB)的各向异性,探讨OSB面内剪切模量动态和静态测试方法,以提供一种快速、简便、重复性好、精度高的动态测试方法测量和分析OSB弹性常数。【方法】应用ANSYS程序计算OSB自由板和悬臂板试件的振形系数,给出振形系数依赖于板长宽比和宽厚比的关系式,通过仿真计算、动态试验和方板静态扭转试验验证其正确性。动态试验测试OSB剪切模量试件从一块整张OSB上下料制作,分为3个方向,即沿整板纵向下料制作的试件(0°或x向)、横向方向下料制作的试件(90°或y向)和沿与纵向呈45°方向下料制作的试件;方板扭转试验测试OSB剪切模量试件沿整板纵向或横向下料制作;动态测试OSB纵向、横向和45°方向弹性模量以及面内剪切模量和45°方向剪切模量。【结果】OSB实测纵向弹性模量是横向弹性模量的2.89倍,45°方向剪切模量小于面内剪切模量。正交各向异性材料方板扭转试验测试剪切模量推算公式需用±45°方向应变测量值的差值进行推算,将其用于OSB,测得的静态剪切模量与动态测试的剪切模量相当吻合。【结论】OSB弹性模量具有方向性,纵向最大,横向最小,45°方向介于二者之间;自由板扭转振形法和悬臂板扭转模态法适用于动态测试OSB面内剪切模量,其正确性得到方板扭转试验验证;0°和90°OSB动态测得的剪切模量几乎相等,可作为OSB面内剪切模量Gxy的估计值;OSB不宜按单向复合材料处理,在理论分析时宜按正交各向异性处理,OSB45°方向的剪切模量G45°相似文献   

The aging effects of water immersion treatments in wet-bending for standardized testing of wood panels

The durability of wood-based panels is one of the most important properties when they are used in residential construction. The main objectives of this study were to investigate the quantitative relationship between the Wet-bending A test and the Wet-bending B test, examine the aging effects of the treatments specified in the wet-bending methods, and discuss the relationship between wet-bending and outdoor aging tests conducted in Shizuoka, Japan. Wet-bending tests, internal bond tests after humidity treatment, and outdoor aging tests in Shizuoka were conducted using eight types of commercial wood-based panels. A linear relationship was found between the load-carrying capacity (LCC) from the Wet-bending A test and the LCC from the Wet-bending B test. The LCC from Wet-bending B could be obtained from LCC from Wet-bending A by multiplying it by 0.9, which may be applicable as a quantitative ratio of aging effects between the two. LCC for methylenediphenyl diisocyanate-bonded panels recovered to almost 100% of the initial strength. A certain relationship was found between the LCC after Wet-bending A and the LCC after a 1-year outdoor exposure in Shizuoka. Internal bond strength showed a good correlation between the JIS-A treatment and the 1-year outdoor exposure treatment.     

Production and properties of Japanese oriented strand board I: effect of strand length and orientation on strength properties of sugi oriented strand board

Oriented strand boards (OSB) were made using sugi wood strand with different lengths at different free fall distance conditions. Strand alignment and mechanical properties of sugi OSB were evaluated. Results obtained can be summarized as follows. The alignment angle distribution was greatly affected by both free fall distance and strand length. It was found that the standard deviation of the angles can be a measure for predicting the distribution when employing the von Mises distribution function with concentration parameter. The Monte Carlo simulation showed an agreement between the theoretical considerations and the experimental results on the strand alignment. The mechanical properties as affected by both strand length and layer structure were determined. Bending properties could be equal in both directions at 25% face layer ratio. Young's modulus obtained by the in-plane vibration method showed almost linear relation to the face layer ratio. No significant differences or only a slight difference was observed for the internal bond strength, plate-shear modulus, and nail resistance properties. Further studies are necessary.     

Applicability of the losipescu shear test on the measurement of the shear properties of wood

We examined the applicability of the Iosipescu shear test for measuring the shear properties of wood. Quarter-sawn board of sitka spruce (Picea sitchensis Carr.) and shioji (Japanese ash,Fraxinus spaethiana Lingelsh. were used for the specimens. Iosipescu shear tests were conducted with two types of specimen whose longitudinal and radial directions coincided with the loading direction. The shear modulus, yield shear stress, and shear strength were obtained and were compared with those obtained by the torsion tests of rectangular bars. The results are summarized as follows: (1) The Iosipescu shear test is effective in measuring the shear modulus and the yield shear stress. (2) To measure the shear strength properly by the Iosipescu shear test, the configuration of specimen and the supporting condition should be examined in more in detail.     

Elastic moduli and stiffness optimization in four-point bending of wood-based sandwich panel for use as structural insulated walls and floors

Several wood-based sandwich panels with low-density fiberboard core were developed for structural insulated walls and floors, with different face material, panel thickness, and core density. The elastic moduli with and without shear effect (E _L, E ₀) and shear modulus (G_b) were evaluated in four-point bending. Generally, the stiffer face, thicker panel, and higher core density were advantageous in flexural and shear rigidity for structural use, but the weight control was critical for insulation. Therefore, optimum designs of some virtual sandwich structures were analyzed for bending stiffness in relation to weight for fixed core densities, considering the manufactured-panel designs. As a result, the plywood-faced sandwich panel with a panel thickness of 95 mm (PSW-T100), with insulation performance that had been previously confirmed, was most advantageous at a panel density of 430 kg/m³, showing the highest flexural rigidity (E _L I = 13 × 10⁻⁶ GNm²) among these panels, where E _L, E ₀, and G _b were 3.5, 5.5, and 0.038 GN/m², respectively. The panel was found to be closest to the optimum design, which meant that its core and face thickness were optimum for stiffness with minimum density. The panel also provided enough internal bond strength and an excellent dimensional stability. The panel was the most feasible for structural insulation use with the weight-saving structure.     

Effect of nanoclay on some applied properties of oriented strand board (OSB) made from underutilized low quality paulownia (Paulownia fortunei) wood

In this study, the effect of nanoclay on some applied properties of oriented strand board (OSB) made from underutilized low quality paulownia wood was investigated. Organo-modified montmorillonite (MMT) at four levels (0, 1, 3 and 5?%) was added to urea formaldehyde (UF) resin. Some chemical properties of paulownia wood (holocellulose, cellulose, lignin and ash contents, pH value and hot and cold water solubility), mechanical [modulus of rupture (MOR), modulus of elasticity (MOE), internal bond strength, screw and nail withdrawal strengths], physical (water absorption and thickness swelling) properties and formaldehyde emission of the strand boards were evaluated. Mechanical properties of all panels complied with the general-purpose OSB minimum property requirements of European Norm. With increasing 5?% nanoclay to UF resin, mechanical and physical properties of the resulting panels improved and formaldehyde emission decreased. However, none of the panels satisfied the thickness swelling and water absorption requirement. The results of X-ray diffraction and transmission electron microscope analysis confirmed the good dispersion of nanoclay in the resulting OSBs. Using paulownia as a fast-growing underutilized species not only can sustain the forests but also can supply raw material to countries facing shortage of wood.     

Deterioration of wood-based boards subjected to outdoor exposure in Tsukuba

Various types of wood-based boards were analyzed for deterioration after being exposed to an outdoor environment for 5 years in Tsukuba, Japan. In phenol–formaldehyde resin bonded particleboard (PB(PF)) and aspen oriented strand board (OSB(aspen)), longer exposure caused a greater reduction in the modulus of rupture and internal bond strength, an increase in the coefficients of variation, and a decrease in 95 % lower tolerance limit at the 75 % confidence level (95TL). Nail-head pull-through and lateral nail resistance were also reduced by outdoor exposure, but their coefficients of variation and 95TL were not significantly affected. In contrast, methylene diphenyl diisocyanate bonded medium density fiberboard (MDF(MDI)) only showed a slight deterioration of these properties even after 5-year exposure, and the coefficients of variation and 95TL hardly changed. After 5-year exposure, the retention of shear load in one-plane at relative displacement of 1.0 mm was high in MDF(MDI) and OSB(aspen) at 93.5 and 78.5 %, respectively, but low in PB(PF) at 41.1 %. As with PB(PF), OSB(aspen) also showed a sharp decrease in the modulus of rupture and internal bond strength, but only slightly reduced shear load in one-plane.     

Fracture energy vs. internal bond strength – mechanical characterization of wood-based panels

Abstract

A new testing method measuring the specific fracture energy of wood-based panels in Mode I is proposed. Three types of wood-based panels, i.e. oriented strand board (OSB), particleboard (PB) and medium density fibreboard (MDF) are investigated, using fracture energy and the industrial European standard method of internal bond strength according to EN 319. Double cantilever beam specimens are notched in the middle layer to introduce an initial crack. To apply tensile load perpendicular to the surface of the panels to open the crack in Mode I specimens were adhesively bonded to steel braces. Besides the calculation of the total fracture energy an advanced analysis of the load–displacement curve was also performed. Results of the fracture energy method were compared to internal bond strength (IB). Specimen shape is optimized for industrial purposes using double cantilever beams, while the determination of the fracture energy is performed by simple integration of the load–displacement curve. While IB showed a large scattering of data, the fracture energy test yielded statistically significant differences between the board types.     

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     

Fatigue in wood-based panels. Part 1: The strength variability and fatigue performance of OSB, chipboard and MDF

Wood-based panels used as floor decking can be exposed to fatigue as well as creep loading. The strength and fatigue performances of three wood-based panel products OSB, chipboard and MDF have been determined in four-point bending. The mean bending strengths were found to decrease in the following order MDF>OSB>chipboard. The bending strength variation within the OSB was considerably greater than that for chipboard and MDF. Normalised with respect to the static strengths, the fatigue performance of the chipboard was superior to that of the OSB, although the two materials have very similar performances at low stress levels. Normalised with respect to the static strengths, the fatigue performance of the MDF was inferior to both materials and at lower stress levels the fatigue performance deteriorated to a greater extent. However, in terms of absolute applied stress, the fatigue performance of the MDF was superior to that of the OSB, which was superior to that of the chipboard. However, as the stress was reduced the difference between the three materials reduced. At low stresses the performances of the three materials were quite similar. Received 5 August 1999     

Structural mechanics of wood composite materials I: Ultrasonic evaluation of internal bond strength during an accelerated aging test

This research attempts to observe indirectly the variation of internal bond characteristics for wood composite materials during accelerated aging test treatment using ultrasonic pulse-transmission techniques. Particleboard (PB) and oriented strandboard (OSB) were the representative specimens. The transit time of the ultrasonic wave propagating through the samples along the nominal length and thickness directions was recorded using an apparatus called PUNDIT (C.N.S. Electronic, London). The transit times were measured in the samples under an oven-dried condition after treating them with boiling water at different treating time stages, and the velocity was then calculated based on the transit time. Examination of the internal bond strength conducted on the same samples was done according to JIS A 5908. A study of the relations among springback, internal bond strength, and velocity indicated that a high correlation existed between ultrasonic velocity measured in the length or thickness direction and the internal bond strength for the PB specimen, but no significant correlation was observed between the velocity measured in the length direction and the internal bond strength for the OSB specimen. The results of this research suggested that ultrasound techniques can be applied to predict or evaluate the internal bond state of some wood-composite materials made of relatively small particles, such as PB especially, during accelerated aging test treatment processes.Part of this paper was presented at the 47th annual meeting of the Japan Wood Research Society, Kochi, April 1997     

不同温湿度条件对人造板理化性能的影响

以强化木地板、中密度纤维板、高密度纤维板、浸渍胶膜纸饰面人造板等5类人造板为试材,研究标准、模拟夏季、模拟冬季等不同温湿度平衡处理条件对上述人造板内结合强度、吸水厚度膨胀率和表面结合强度值等理化性能检测指标结果的影响。结果表明,高温高湿平衡处理使人造板的力学强度增加,吸水厚度膨胀率降低;低温低湿平衡处理使人造板力学强度降低,吸水厚度膨胀率增加;不同平衡处理条件下强化木地板吸水厚度膨胀率差异较大;对饰面板表面结合强度的影响大于素板。     

Effect of thermo-mechanical refining on properties of MDF made from black spruce bark

The effects of thermo-mechanical refining conditions on the properties of medium density fiberboard (MDF) made from black spruce (Picea mariana) bark were evaluated. The bark chips were refined in the MDF pilot plant of Forintek Canada Corporation under nine different refining conditions in which preheating retention time was adjusted from 3 to 5 to 7 min and steam pressure was set at either 0.6, 0.9 or 1.2 MPa. The resulting bark fibers were blended with 12% UF resin (based on oven-dry fiber weight) using a mechanical blender. The resinated fibers were manually formed into fiber mats and hot-pressed into MDF panels using consistent parameters. Two panels for each refining condition were produced, resulting in a total of 18 panels. Analysis of variance (ANOVA) was used to analyze the significance of factors. Regression coefficients and 3D contour plots were used to quantify the relationship between panel properties and the two test factors. The results from this study indicated that the preheating retention time was a significant factor for both modulus of rupture (MOR) and modulus of elasticity (MOE), the steam pressure was a significant factor for internal bond strength (IB), MOR and MOE, whereas both factors were insignificant for thickness swelling, water absorption and linear expansion. The properties of MDF panels were quadratic functions of retention time and steam pressure. Compared to the ANSI standard for 120-grade MDF, most panels with a nominal density of 950 kg/m³ had very high IB (>1 MPa) and acceptable MOR, MOE and dimension stabilities. These results suggest that black spruce bark residues can be considered as a potentially suitable raw material for manufacturing MDF products.     

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.     

The evaluation of long-term mechanical properties of wood-based panels by indoor exposure tests

Wood-based panels such as plywood, oriented strand board, particleboard, and medium-density fiberboard are used for roof, wall and floor sheathing materials in residential construction. However, the service life of these panels is still unknown due to the lack of long-term durability data. In this paper, test results from six different indoor exposure experiments were integrated to investigate the long-term durability of wood-based panels. The indoor exposure tests lasted for a maximum of 10 years, providing the panels with the changes in moisture content that ranged between 5 and 18%. The reduction in mechanical properties was determined to be in the range of 0–16% for the bending strength, 3–22% for the modulus of elasticity, 11–31% for the internal bond strength and 0–8% for the nail-head pull-through strength. No reduction was recognized for the lateral nail resistance. Furthermore, the concept of deterioration intensity (DI) based on the moisture content history was introduced to predict the long-term durability of the panels, and various calculation methods for DI were discussed so as to increase the correlativity of this property with the reduction in a mechanical property.     

Modified method for evaluating weathering intensity using outdoor exposure tests on wood-based panels

The deterioration of wood-based panels at eight sites in Japan over 7?years of outdoor exposure was investigated. In particular, the modulus of rupture (MOR) retention and internal bond strength (IB) retention after 7?years of exposure were compared among panels and sites. The deterioration of panels was greater in southern Japan than in northern Japan. The strength retentions in northern Japan decrease linearly, while those in southern Japan decreased exponentially. To quantify regional differences, deterioration rates were calculated based on three different weather conditions (precipitation, temperature, and sunlight hours), and the significance of each of these parameters on panel deterioration was determined. We found that the correlation coefficients between both IB and MOR retention and weathering intensity were the same whether we used 10-day, monthly, or daily weathering data.     

Properties of kenaf core binderless particleboard reinforced with kenaf bast fiber-woven sheets

Kenaf composite panels were developed using kenaf bast fiber-woven sheets as top and bottom surfaces, and kenaf core particles as core material. During board manufacture, no binder was added to the core particles, while methylene diphenyldiisocyanate resin was sprayed to the kenaf bast fiber-woven sheet at 50 g/m² on a solids basis. The kenaf composite panels were made using a one-step steam-injection pressing method and a two-step pressing method (the particleboard is steam pressed first, followed by overlaying). Apart from the slightly higher thickness swelling (TS) values for the two-step panels when compared with the one-step panels, there was little difference in board properties between the two composite panel types. However, the two-step pressing operation is recommended when making high-density composite panels (>0.45 g/cm³) to avoid delamination. Compared with single-layer binderless particleboard, the bending strengths in dry and wet conditions, and the dimensional stability in the plane direction of composite panels were improved, especially at low densities. The kenaf composite panel recorded an internal bond strength (IB) value that was slightly low because of the decrease of core region density. The kenaf composite panel with a density of 0.45 g/cm³ (one-step) gave the mechanical properties of: dry modulus of rupture (MOR) 14.5 MPa, dry modulus of elasticity (MOE) 2.1 GPa, wet MOR 2.8 MPa, IB 0.27 MPa, TS 13.9%, and linear expansion 0.23%.     

Comparative study on measurement of elastic constants of wood-based panels using modal testing: choice of boundary conditions and calculation methods

Modal testing based on the theory of transverse vibration of orthotropic plate has shown great potentials in measuring elastic constants of panel products. Boundary condition (BC) and corresponding calculation method are key in affecting its practical application in terms of setup implementation, frequency identification, accuracy and calculation efforts. To evaluate different BCs for non-destructive testing of wood-based panels, three BCs with corresponding calculation methods were investigated for measuring their elastic constants, namely in-plane elastic moduli (E _x , E _y ) and shear modulus (G _xy ). As a demonstration of the concept, the products used in this study were oriented strand board (OSB) and medium density fiberboard (MDF). The BCs and corresponding calculated methods investigated were, (a) all sides free (FFFF) with one-term Rayleigh frequency equation and finite element modeling, (b) one side simply supported and the other three free (SFFF) with one-term Rayleigh frequency equation, (c) a pair of opposite sides along minor strength direction simply supported and the other pair along major strength direction free (SFSF) with improved three-term Rayleigh frequency equation. Differences between modal and static results for different BCs were analyzed for each case. Results showed that all three modal testing approaches could be applied for evaluation of the elastic constants of wood-based panels with different accuracy levels compared with standard static test methods. Modal testing on full-size panels is recommended for developing design properties of structural panels as it can provide global properties.     

Evaluation of the weathering intensity of wood-based panels under outdoor exposure

In this study, the deterioration of wood-based panels at eight sites in Japan was investigated using outdoor exposure tests. In particular, the modulus of rupture (MOR) retention and internal bond strength (IB) retention after 5-year exposures were compared among panels and sites. The deterioration of panels located in southern Japan was higher than that of panels in northern Japan. To quantify the regional differences, the deterioration rates were calculated; the values showed clear regional differences. The deterioration rate for areas that receive much rain in the summer was higher than the rates for other sites. To eliminate regional differences, we carried out an analysis in terms of the “weathering intensity,” a factor which combines weather conditions (precipitation and temperature). Panels for which deterioration progressed extensively during exposure periods showed a strong correlation between strength retention and the weathering intensity. The significance of these parameters is discussed.     

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.