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1.
《Wood material science & engineering》2013,8(2):83-89
Abstract To study the effect of grain angle on the adhesive bond strength in wood, three-part Norway spruce wood specimens were bonded and tested in tension. The two axially orientated outer parts of the specimens were joined with the middle part by means of three adhesives typically used for load-bearing constructions, i.e. one-component polyurethane (PUR), melamine–urea–formaldehyde (MUF) and phenol–resorcinol–formaldehyde (PRF). The grain angle of the middle part was varied from 0° (end grain to end grain) to 90° (flat grain to end grain) in incremental steps of 10°. In general, PRF- and MUF-bonded samples exhibited highest tensile strength at end grain to end grain orientation of the three parts, while specimens bonded with PUR showed only 25% of the strength measured for PRF and MUF, respectively. At high grain angles (90°) all specimens showed similar strength values in the range of 30% of maximum strength of MUF- and PRF-bonded specimens. To explain the changing strength levels at different grain angle a composite failure criterion was applied. 相似文献
2.
《Wood material science & engineering》2007,2(2):83-89
To study the effect of grain angle on the adhesive bond strength in wood, three-part Norway spruce wood specimens were bonded and tested in tension. The two axially orientated outer parts of the specimens were joined with the middle part by means of three adhesives typically used for load-bearing constructions, i.e. one-component polyurethane (PUR), melamine-urea-formaldehyde (MUF) and phenol-resorcinol-formaldehyde (PRF). The grain angle of the middle part was varied from 0° (end grain to end grain) to 90° (flat grain to end grain) in incremental steps of 10°. In general, PRF- and MUF-bonded samples exhibited highest tensile strength at end grain to end grain orientation of the three parts, while specimens bonded with PUR showed only 25% of the strength measured for PRF and MUF, respectively. At high grain angles (90°) all specimens showed similar strength values in the range of 30% of maximum strength of MUF- and PRF-bonded specimens. To explain the changing strength levels at different grain angle a composite failure criterion was applied. 相似文献
3.
Veneer drying is one of the most important stages in the manufacturing of veneer-based composites such as plywood and laminated veneer lumber. Due to the high drying costs, increased temperatures are being used commonly in plywood industry to reduce the overall drying time and increase capacity. However, high drying temperatures can alter some physical, mechanical and chemical characteristics of wood and cause some drying-related defects. In this study, it was attempted to predict the optimum drying temperature for beech and spruce veneers via artificial neural network modeling for optimum bonding. Therefore, bonding shear strength values of plywood panels manufactured from beech and spruce veneers dried at temperatures of 20, 110, 150 and 180 °C were obtained experimentally. Then, the intermediate bond strength values based on veneer drying temperatures were predicted by artificial neural network modeling, and the values not measured experimentally were evaluated. The optimum drying temperature values that yielded the highest bonding strength were obtained as 169 °C for urea formaldehyde and 125 °C for phenol formaldehyde adhesive in beech plywood panels, while 162 °C for urea formaldehyde and 151 °C for phenol formaldehyde in spruce plywood panels. 相似文献
4.
ABSTRACTThe effects of a fire-retardant treatment (FRT) and wood grain on three-dimensional changes of aircraft sandwich panels were evaluated. Unvarnished and varnished panels having the outer decorative layer made with bubinga (Guibourtia spp.) were studied. Half of the samples from each type of panel received an FRT (phosphate-based) on all three layers of the decorative plywood. The other half had the two inner layers treated and the outer layer untreated. Three different figures formed by the rotary cutting and grain orientation were identified and separately studied on veneer surfaces. Samples pre-conditioned to 20°C and 40% relative humidity (RH) underwent an adsorption (25°C, 90% RH) and then a desorption (25°C, 40% RH) treatments. Changes in moisture content (MC), swelling, shrinkage, roughness, and waviness were measured after each moisture exposure condition. The results showed that the FRT increased significantly MC, swelling, and shrinkage of unvarnished and varnished panels. This treatment as well as the type of wood figure affected roughness and waviness variations of unvarnished panels. However, the effects of these two factors were not noticeable once panels were varnished. 相似文献
5.
Particleboard made from hammer milled black spruce bark residues 总被引:1,自引:0,他引:1
Summary The disposal of bark residues is an important problem for the forest industry. An important proportion of the bark produced
by the paper and lumber industries is used for energy production, but a significant amount of bark is still unused. The objective
of this study was to determine the technical feasibility of making particleboards from black spruce bark residues bonded with
urea formaldehyde resin and meeting the indoor performance requirements for wood particleboards. In the positive case, this
would define a new use for black spruce bark residues. Fresh black spruce bark residues were obtained from a sawmill located
in the northeast part of the province of Quebec, Canada. The bark was kiln-dried at 60 °C, the particles were generated from
a hammermill and sieved. Particles from 0.02 to 2.0 mm were used in the surface layers and particles from 2.0 to 6.0 mm were
used in the core layer. Particleboards of 540 × 560 × 16 mm were made with a laboratory hot press following a factorial design
with two manufacturing variables at three levels: (1) wood particles content of the surface layers (0, 25, 50 percent); and
(2) UF resin content of the surface layers (12, 14 and 16 percent) with a UF resin content in the core of 8 percent. This
resulted in a factorial design of 9 different combinations repeated 3 times for a total of 27 boards. It was observed that
the heating kinetics varied according to the wood particles content in the surface layers. The compression ratio of the mat
and the board internal bond, modulus of elasticity, modulus of rupture, linear expansion and thickness swell were determined.
The results show that it is technically possible to make particleboard from bark residues meeting the American National Standard
Institute indoor requirement for wood particleboard under certain conditions. The modulus of rupture of the boards was the
most critical property in this study. The best mechanical properties were obtained with a 50 percent wood content and 14 percent
resin content in the surface layers. The particleboards produced in this study did not meet the minimal requirements for linear
expansion. The temperature measurements performed in the core of the mat during hot pressing show that heat transfer improves
with an increase in wood particles content in the surface layers.
Received 15 June 1998 相似文献
6.
《Wood material science & engineering》2013,8(2):90-95
Abstract In a previous study it was shown that the mechanical stability of an end-grain joint bonded with a one-component polyurethane adhesive (PUR) was insufficient compared with melamine–urea–formaldehyde and phenol–resorcinol–formaldehyde bonding. Based on this, the aim of this study was to improve the mechanical stability of the end-grain joint by means of a hydroxymethylated resorcinol (HMR) primer and by increasing the spreading quantity. To study the effect of HMR and the increased spreading quantity on the adhesive bond strength of end-grain to end-grain-bonded wood samples, three-part Norway spruce wood specimens were tested in tension. Before bonding, each end-grain surface was treated with an aqueous solution of HMR. The two axially orientated outer parts of the specimens were jointed with the middle part using a PUR adhesive. Compared with untreated, i.e. non-primed samples, the tensile strength of HMR-treated specimens was more than doubled. Furthermore, a positive effect of increased adhesive spread was shown for untreated PUR-bonded samples. An increase in adhesive spread by a factor of 1.6 led to an improvement in tensile strength by a factor of about 2.6. 相似文献
7.
Laminated products, such as laminated veneer lumber (LVL) or plywood (PW), have become important recently. The objective of
this study was to determine and compare properties of panels fabricated with veneers of Gmelina arborea trees in a fast-growth plantation and glued with phenol formaldehyde resin. The results showed that LVL and PW physical and
mechanical properties are comparable to those of solid wood with a specify gravity of 0.60. Moreover, these panels can be
cataloged into group 2 of PS 1–95 of the Voluntary Products Standard of the United States. The difference in physical properties
was not statistically significant between LVL and PW panels, except for water absorption. Some mechanical properties, such
as hardness and glue-line shear, modulus of rupture in perpendicular flexure, nail and screw withdrawal parallel, and perpendicular
strength, were statistically different between LVL and PW. However, no differences were established for the modulus of elasticity,
tensile strength parallel to the surface, or tensile strength perpendicular to the surface. The differences were attributed
to the venners’ orientation in the panels studied. 相似文献
8.
Dong-heub Lee Myung Jae Lee Dong-Won Son Byung-Dae Park 《Wood Science and Technology》2006,40(3):228-236
The extended use of woods treated with traditional or alternative preservatives for exterior applications requires an assessment
of wood adhesive performance. This study attempts to evaluate the performance of wood adhesives for woods treated with various
waterborne preservatives. Two softwood species, i.e. Korean pine (Pinus koraiensis Sieb. et Zucc.) and Japanese Larch (Larix leptolepis [Sieb. et Zucc.] Gordon) were treated with copper–chrome–arsenic (CCA), CB-HDO, or copper azole (CY), and then bonded with
four different wood adhesives such as urea–melamine–formaldehyde (UMF) resin, melamine–formaldehyde (MF) resin, phenol–formaldehyde
(PF) resin, and resorcinol–formaldehyde (RF) resin. The performance of these adhesives was evaluated by measuring the dry
shear strength of adhesive-bonded wood block on compression. Both UMF and MF resins produced a relatively strong adhesive
strength for CY-treated pine and larch woods. The PF resin also produced good bond strength when bonded with either larch
wood treated with CY or pinewood treated with CB-HDO. The best result was obtained when the CB-HDO-treated woods were bonded
with RF resin. For a better bond strength development, a proper combination of adhesive, preservative, and wood species should
be selected by taking into consideration of the characteristics of these three parameters as well as their interactions. 相似文献
9.
Summary A simple model, based on the use of transformations of second-order tensors, is presented in this paper to predict the failure
mode of wood members stressed in various degrees of parallel-and perpendicular-to-grain tension and parallel-to-grain shear.
This type of loading is indicative of structural wood members with cross grain or grain deviations in the vicinity of knots
subjected to bending or tension. The model is based on the assumptions that failure is dictated by the presence of any of
the aforementioned stresses that exceed the clear wood strength in that mode and that failure does not result from stress
interactions. The magnitudes of the applied stresses are normalized relative to the wood strength in that mode. The ratio
of applied stress to material strength that is greatest at any particular angle of load to grain is presumed to be the failure
mode at that angle. To verify model predictions, optical and microscopic analyses of surfaces of failed specimens loaded in
uniaxial tension at angles between 0° and 90° to grain were compared to previously obtained, or otherwise known, surfaces
of specimens tested in tension and shear. Specimens tested at various angles to grain demonstrated failed surfaces very much
like those associated with specimens loaded in the modes predicted by the model. 相似文献
10.
11.
人工林杉木和杨树木材物理力学性质的株内变异研究 总被引:4,自引:0,他引:4
按照中国国家标准研究杉木和I-214杨树木材的抗弯弹性模量、抗弯强度、顺纹抗压强度和密度,同时按照日本国家标准研究2个树种的顺纹抗剪强度.结果表明:杉木的抗弯强度、顺纹抗压强度和密度由胸高直径处向上呈波浪形增加,抗弯弹性模量则稳定降低,但不同高度间杉木的物理力学性质没有显著差异;近树皮处木材的物理力学性质高于近髓心处木材,并有极显著差异.对于I-214杨树,只有抗弯弹性模量从髓心到树皮逐渐增加,其他的物理力学性质,最小值在从髓心到树皮的过渡区,最大值在近树皮处,从髓心到树皮,杨树的物理力学性质有极显著的差异.杉木和杨树的径面顺纹抗剪强度从髓心到树皮有极显著差异,并且近树皮的高于近髓心的木材,而弦面顺纹抗剪强度从髓心到树皮没有显著差异.木材密度与力学性质有很好的线性相关关系,木材密度是一个很好的力学强度的预测手段. 相似文献
12.
We examined the bending and shear properties of compressed wood using small and clear specimens of Sitka spruce (Picea sitchensis Carr.). For measuring the bending properties, three-point bending tests were conducted under the span/depth ratio of 14,
which is standardized in the American Society for Testing and Materials [ASTM D143-94 (2005a)] and Japanese Industrial Standards
[JIS Z2101-94 (1994)]. In the bending test, the load, deflection at the midspan, and strain at the bottom of the midspan were
simultaneously measured, and Young’s modulus and bending strength were obtained by elementary beam theory. For obtaining the
shear modulus and shear strength, asymmetric four-point bending tests were conducted using the specimens with rectangular
and side-grooved cross sections, respectively, and the influence of the compression ratio on the shear properties was examined.
The results are summarized as follows: (1) Young’s modulus increased with increasing compression ratio when it was determined
by the load–strain relation. Nevertheless, this tendency was rather obscured when Young’s modulus was determined by the load–deflection
relation. Hence, it is preferable that Young’s modulus is measured from the load–strain relation. (2) The shear modulus in
the longitudinal–tangential plane was maximum at the compression ratio of 50%, whereas that in the longitudinal–radial plane
was minimum at the compression ratio of 50%. (3) The influence of the compression on the bending and shear strength ratio
was not significant. 相似文献
13.
Preparation of carbon fibers from liquefied wood 总被引:1,自引:1,他引:0
Carbon fibers are prepared from liquefied wood by adding hexamethylenetetramine and soaking in a solution containing hydrochloric
acid and formaldehyde as main components. Structure evolution of carbon fibers from liquefied wood (LWCFs) is investigated
by using FTIR and XRD. The results show that the structure of the precursor fibers from liquefied wood has been completely
changed after carbonization. The apparent crystallite size (L
c(002)) and the apparent layer-plane length parallel to the fiber axis (L
a(100)) gradually increase during carbonization. Carbon fibers with the maximum tensile strength of 1.7 GPa are obtained under certain
carbonization conditions. At the same time, it is also found that 600–800°C is the critical stage at which the specific surface
area of LWCFs changes. 相似文献
14.
WANG Xiaohuan HUANG Rongfeng ZHENG Hongkui LI Hua LIU Xiuying . Research Institute of Wood Industry Chinese Academy of Forestry Beijing P. R. China . Inner Mongolia Agricultural University Hohhot P. R. China 《中国林业科技(英文版)》2006,5(4):16-22
INTRODUCTION The main body of ancient architecture is wood construction in China, and the main bearing components of the buildings usually use timber, such as pillar, beam, purlin, crossbeam and rafter. Timber is a kind of biomaterial and will be damaged by fungal attack or insects after long time use, which will cause wood frames destroyed ultimately. Timber decay not only exists in its surface, but also usually begins with the inner of wood. It is therefore imperative to consider using … 相似文献
15.
Surface quality and gluing performance of black spruce samples prepared by peripheral straight-edge knife planing and sanding were studied. Four wavelengths (1.5, 1.9, 3.1, and 6.5 mm) and four rake angles (15°, 20°, 25°, and 30°) were tested for peripheral planing. Three feed speeds (4, 10.5, and 17 m/min) and three grit size sandpapers (80, 100, and 120) were studied for sanding. The resulting surfaces were glued with an isocyanate adhesive and tested to evaluate their gluing performance (shear strength and percent wood failure). Results revealed that planing with a rake angle of 20° and wavelengths of up to 3.1 mm produced wood surfaces with adequate glueline shear strength. Sanding with 80-grit sandpaper produced the best glueline shear strength, regardless of feed speed. After accelerated aging, the loss of gluing performance was lower for the sanded samples compared with that of planed samples. In general, sanding process produced better wood surfaces for bonding with the adhesive studied. 相似文献
16.
The bending properties of split bamboo culm were compared with those of spruce and beech wood specimens. The bamboo allowed
large flexural deformation since its outer layer retains the tensile stress while the softer inner layer undergoes large compressive
deformation. The results suggested that the combination of the fiber-rich outer part and the compressible inner part was responsible
for the flexural ductility of split bamboo. To clarify the compressible nature of the inner part of bamboo, the longitudinal
surfaces of the bamboo and wood specimens were microscopically observed before and after a large longitudinal compression.
Although the wood specimens showed serious and localized buckling, the inner part of the bamboo specimens showed no such visible
buckling. In the latter case, the foam-like parenchyma cells absorbed the large compressive deformation by their microscopic
buckling and simultaneously, the alignment of sclerenchyma fibers was maintained by the surrounding parenchyma matrix. The
flexural elasticity of the bamboo was compared to that of the wood in respect of remaining strain during cyclic bending tests.
No clear difference was recognized between their remaining strains. This fact indicated that the bamboo was not so flexible
elastically, although its fiber–foam combination and intelligent fiber distribution improve flexural ductility. 相似文献
17.
Ingela Bjurhager Lars A. Berglund Stig L. Bardage Björn Sundberg 《Journal of Wood Science》2008,54(5):349-355
Functional analysis of genes and proteins involved in wood formation and fiber properties often involves phenotyping saplings
of transgenic trees. The objective of the present study was to develop a tensile test method for small green samples from
saplings, and to compare mechanical properties of juvenile European aspen (Populus tremula) and hybrid aspen (Populus tremula × tremuloides). Small microtomed sections were manufactured and successfully tested in tension parallel to fiber orientation. Strain was
determined by digital speckle photography. Results showed significantly lower values for juvenile hybrid aspen in both Young’s
modulus and tensile strength parallel to the grain. Average Young’s moduli spanned the ranges of 5.9–6.6 and 4.8–6.0 GPa for
European aspen and hybrid aspen, respectively. Tensile strength was in the range of 45–49 MPa for European aspen and 32–45
MPa for hybrid aspen. The average density (oven-dry) was 284 kg/m3 for European aspen and 221 kg/m3 for hybrid aspen. Differences in mechanical properties correlated with differences in density.
Part of this article was presented at the 3rd International Symposium on Wood Machining, May 21–23, 2007, Lausanne, Switzerland 相似文献
18.
Daniel Keunecke Walter Sonderegger Karol Pereteanu Thomas Lüthi Peter Niemz 《Wood Science and Technology》2007,41(4):309-327
Despite the exceptional position of yew among the gymnosperms concerning its elastomechanical properties, no reference values
for its elastic constants apart from the longitudinal Young’s modulus have been available from literature so far. Hence, this
study’s objective was to determine the Young’s moduli E
L, E
R and E
T and the shear moduli G
LR, G
LT and G
RT of yew wood. For that purpose, we measured the ultrasound velocities of longitudinal and transversal waves applied to small
cubic specimens and derived the elastic constants from the results. The tests were carried out at varying wood moisture contents
and were applied to spruce specimens as well in order to put the results into perspective. Results indicate that E
L is in the same order of magnitude for both species, which means that a high-density wood species like yew does not inevitably
have to have a high longitudinal Young’s modulus. For the transverse Young’s moduli of yew, however, we obtained 1.5–2 times,
for the shear moduli even 3–6 times higher values compared to spruce. The variation of moisture content primarily revealed
differences between both species concerning the shear modulus of the RT plane. We concluded that anatomical features such
as the microfibril angle, the high ray percentage and presumably the large amount of extractives must fulfil important functions
for the extraordinary elastomechanical behaviour of yew wood which still has to be investigated in subsequent micromechanical
studies. 相似文献
19.
In view of its high density, yew wood has a remarkably low longitudinal Young’s modulus, which makes it unique among coniferous
woods. However, the elastic response of yew related to other load directions is largely unknown. Therefore, our goal was to
comprehensively characterise the three-dimensional elastic behaviour of yew wood. To achieve this, we performed tensile tests
on dog-bone-shaped yew specimens and determined the three Young’s moduli and six Poisson’s ratios using a universal testing
machine and a digital image correlation technique. All tests were also applied to spruce as reference species. After including
the shear moduli determined in a prior study by our group, all elastic engineering parameters of yew and spruce were ascertained.
Based on these values, the three-dimensional elastic behaviour was describable with deformation bodies and polar diagrams.
Evaluating these illustrations revealed that yew had a lower stiffness only in the longitudinal direction. In all other three-dimensional
directions, spruce was clearly more compliant than yew. Particularly, in the radial–tangential plane, both species varied
largely in their degree of anisotropic elasticity. All mentioned differences between yew and spruce originate at the microstructural
level. 相似文献
20.
The effects of temperature and moisture content on selected mechanical properties associated with the chipping process were evaluated. In chipping, mechanical properties such as shear parallel to the grain, cleavage, and bending are involved. Matched samples of heartwood and sapwood were obtained from freshly harvested logs of black spruce and balsam fir to determine the variation of the studied mechanical properties between ?30 and 20 °C, at intervals of 10 °C. Moisture content (MC), basic density (BD), and annual ring width (RW) were measured for each sample. For both wood species, temperature had a significant effect on all mechanical properties under freezing conditions (below 0 °C). This effect was more important for sapwood than for heartwood, which was explained by the difference in MC between these two types of wood. Between 0 and 20 °C, temperature and type of wood did not show any significant effect on the mechanical properties. Multiple regression models were obtained to predict the mechanical properties. These regressions showed that MC was the most important factor to explain the mechanical properties below 0 °C. However, for temperatures of 0 °C and higher, BD was the principal factor to predict the mechanical properties. RW was not a significant factor to predict any mechanical property. Cleavage was the most sensitive one to changes in temperature followed by shear, modulus of rupture, and modulus of elasticity. These results could be of great importance in the chipping process. 相似文献