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1.
Han-Min Park Masami Fushitani Keiichi Sato Takafumi Kubo Hee-Seop Byeon 《Journal of Wood Science》2006,52(3):220-229
To improve the performance of cross-laminated woods, 30 types of three-ply parallel-laminated and cross-laminated woods were
prepared from five species with various densities and shear compliances in cross section, and their bending creep performances
were investigated on the basis of our previous research in cross-laminated wood made with sugi (Japanese cedar). The creep
deformation perpendicular to the grain was decreased by cross laminating. The creep deformation perpendicular to the grain
of parallel-laminated woods (P⊥ type), that perpendicular to the grain of face laminae of cross-laminated woods (C⊥ type), and also that parallel to the grain of face laminae of cross-laminated woods (C║ type) tended to decrease with increasing density of species used for perpendicular-direction lamina. It was found that the
extent of the decrease was greater in creep deformation than in initial deformation. The degrees of anisotropy for both deformations
of laminated wood were markedly decreased by cross laminating. The extent of the decrease was much greater in creep deformation
than in initial deformation and considerably smaller in buna with higher density than in sugi with lower density. The measured
values of initial deformation and creep deformation of C⊥ type were almost equal to the calculated values obtained from the measured values of parallel-laminated woods, whereas the
measured values of both deformations of C║ type were much greater than their calculated values and increased markedly with increasing shear compliance in cross section
of perpendicular-direction lamina used for core. The ratios of the average of measured values to the calculated value of C║ type ranged from 1.05 (katsura) to 1.50 (sugi) in initial deformation and from 1.30 (katsura) to 3.69 (sugi) in creep deformation.
This result can be explained as the effect of deflection caused by shear force. 相似文献
2.
Kosei Ando Mayu Mizutani Yusuke Taniguchi Hiroyuki Yamamoto 《Journal of Wood Science》2013,59(4):290-298
To understand the viscoelasticity of wood three dimensionally, matched samples of Japanese cypress were loaded in uniaxial tensile creep in the longitudinal (L), radial (R), and tangential (T) directions at approximately 9.7 % equilibrium moisture content. Longitudinal and transverse strains were measured for the determination of viscoelastic Poisson’s ratios and three-dimensional viscoelastic compliance tensors concerning the normal strain. The changes in the transverse strains showed the same tendencies as those in the longitudinal strains, in all directions of loading. That is, during creep, the absolute value of transverse strain continued to increase with the gradual reduction in the increase rate; immediately after the removal of the load, it recovered rapidly, after which it continued to recover slowly. The transverse strain increased most easily in the T direction, followed by R and L, during creep. All the viscoelastic Poisson’s ratios and the absolute values of all elements of the viscoelastic compliance increased logarithmically with creep time. The three-dimensional viscoelastic compliance matrix for Japanese cypress is concluded to be asymmetric. 相似文献
3.
温度对重组竹短期受压蠕变性能的影响 总被引：1，自引：0，他引：1
通过对重组竹受压试件进行短期蠕变试验,研究温度对重组竹受压试件蠕变特性及蠕变规律的影响。针对不同应力水平下温度对重组竹短期受压蠕变的影响,研究了在同一应力水平7.5%下,重组竹在5种不同温度下的24 h顺纹受压蠕变性能;进一步比较了重组竹在应力水平为7.5%,15%,30%且温度分别为25,50,75℃情况下的24 h顺纹短期受压蠕变特点。最后,采用Burgers模型对上述不同温度变量和不同应力水平变量下重组竹短期受压蠕变曲线进行拟合分析。结果表明:在重组竹顺纹受压蠕变中,温度和材料应力水平越高,瞬时弹性变形越大,重组竹蠕变应变总量越大,重组竹抵抗蠕变性能越弱,且较高温度和较高应力水平的同时作用会对重组竹构件产生不利影响;Burgers模型的拟合决定系数基本均在0.98以上,说明Burgers模型能够较准确地描述温度对重组竹短期受压蠕变曲线特性的影响。根据试验与拟合曲线特性可知,重组竹顺纹受压蠕变中弹性变形占80%以上,说明在不同温度下重组竹顺纹受压蠕变中弹性变形占主要部分,随着温度的升高,弹性变形有所下降,黏性变形逐渐增加。 相似文献
4.
Fibre morphological effects on mechano-sorptive creep 总被引：2，自引：2，他引：0
The increased creep rate of paper under load during moisture cycling conditions as compared to that at high constant humidity
is a problem in the use of packaging materials. In order to investigate the influence of morphological factors of the fibres
on the occurrence and magnitude of this phenomenon, i.e. the occurrence of mechano-sorptive creep, studies on wood fibres
isolated from different parts of spruce wood were performed. Thus, creep properties were studied on earlywood and latewood
fibres from both juvenile wood and mature wood. In general, latewood fibres showed a higher degree of mechano-sorptive creep
than earlywood fibres, and mature wood showed a higher degree of mechano-sorptive creep than juvenile fibres. The difference
in mechano-sorptive creep rate between different fibres was shown to be correlated to the differences in fibril angle. The
smaller the fibril angle the higher was the mechano-sorptive creep ratio. It was suggested that at fibril angles approaching
45° wood fibres do not exhibit mechano-sorptive creep. 相似文献
5.
D. J. Robson 《Wood Science and Technology》1989,23(3):229-235
Summary Tensile creep of 100 m thick wood strips cut parallel to the grain was measured using a high resolution high accuracy creep apparatus. Rigorous attempts were made in both design and use of the apparatus to reduce errors to a minimum: the standard deviation of the random errors about a smoothed curve was assessed as 0.34 m. By comparing elongation of strips under load with control strips at zero load viscous and visco-elastic elongation may be accurately measured. 相似文献
6.
T. Nakano 《Journal of Wood Science》1999,45(1):19-23
The creep behavior of wood during water adsorption was mathematically analyzed based on the excitation response theory. The creep change
u
(t), obtained by subtracting an instantaneous complianceJ
u
(0) from a creep complianceJ
u
(t), was linear in terms of moisture content at a steady state of moisture and was separable into two functions of time and moisture content. The creep compliance, however, was nonlinear. The creep change during water adsorption was obtained by applying the excitation-response theory to the creep change in a steady state of moisture. The equation was formally equal to the results reported so far. By using the derived equations, it was theoretically proved that the change in creep compliance during water adsorption from moisture contentu
0 tou
1 is always greater than the difference between creep compliance atu
0 and that at u, in the steady state. 相似文献
7.
We investigated the temporal changes in creep and stress relaxation behavior in both microscopic crystalline cellulose and macroscopic strain of wood specimen using Japanese cypress (Chamaecyparis obtusa Endl.) to understand the viscoelastic properties of wood cell walls. Specimens 600 µm in thickness were observed by the X-ray diffraction and submitted to tensile load. The crystal lattice strain of (004) plane and macroscopic strain of specimen were continuously detected during creep and stress relaxation tests. It was found that the creep compliance based on macroscopic strain showed a gradual increase after instantaneous deformation due to loading and then the parts of creep deformation remained as permanent strain after unloading. On the other hand, crystal lattice strain showed a different behavior for macroscopic strain; it kept a constant value after instantaneous deformation due to loading and then increased gradually after a certain period of time. These differences between macroscopic and microscopic levels were never found in the stress relaxation tests in this study. Relaxation modulus at the macroscopic level only showed a decreasing trend throughout the relaxation process. However crystal lattice strain kept a constant value during the macroscopic relaxation process. In addition, the microfibril angle (MFA) of wood cell wall has a role of mechanical behavior at microscopic level; crystal lattice strains were smaller with increasing MFA at both creep and relaxation processes. Creep compliance and stress relaxation modulus at the macroscopic level decreased and increased with increasing MFA, respectively. Our results on the viscoelastic behavior at microscopic level evidenced its dependency on MFA. 相似文献
8.
Bending creep behavior of wood under cyclic moisture changes 总被引：1，自引：0，他引：1
Yaguang Zhou Masami Fushitani Takafumi Kubo Masayuki Ozawa 《Journal of Wood Science》1999,45(2):113-119
This study examined the bending creep behavior in the longitudinal direction of six species under cyclic moisture content (MC) changes. For each species, tests were made at 20°C with five cyclic relative humidity changes between 65% and 95%, beginning from moisture adsorption. A load corresponding to 25% of short-term breaking load of the species was applied to the radial section of each specimen with four-point bending. The effect of MC change on instantaneous compliance was also investigated under the same condition. The quantitative relation between mechano-sorptive (MS) compliance and MC change was examined, and the material parameter KM for the relation in specific sorption was determined. Results indicated that the total compliance in the six species with different behavior increases with sorption time. As an integral part of total compliance, instantaneous compliance changes linearly with MC and influences to a greater or lesser extent the total compliance behavior. In general, with increasing MC change, the MS compliance linearly increases during the first adsorption and all desorption and decreases slightly during subsequent adsorption. The material parameterK
M varies markedly not only with species but also with specific sorption. The first adsorption causes the largest deformation, followed by desorption.This paper was presented at the 48th annual meeting of the Japan Wood Research Society in Shizuoka, Japan. April 1998 相似文献
9.
The factors affecting mechano-sorptive creep of wood and paper have been investigated for a long time. It has also been argued that single wood fibres do not exhibit mechano-sorptive creep and that the reasons for the accelerated creep under moisture cycling conditions instead are related to the bonds between the fibres. In order to examine the relevance of this argument, measurements on single pulp fibres of different composition were performed in tension, and the mechano-sorptive creep was compared to that of papers made from the same source of pulp fibres. All fibres tested were found to exhibit an increased creep rate during moisture cycling as compared to constant humidity conditions. Thus, pulp fibres show mechano-sorptive creep and in this sense behave similar to solid wood or paper products made thereof. A linear relation between the creep strain rate during cyclic humidity and the creep strain rate at a constant humidity was also noted for both fibres and paper. This relation was not affected by changes in hemicelluloses content or composition, neither for fibres nor for papers made of these fibres. However, in all cases, papers showed a much higher mechano-sorptive creep than the corresponding fibres they were made of. 相似文献
10.
In order to investigate the effect of different reagents on changes of the crystalline region and amorphous region (Matrix) in wood cell walls, the creep behavior of Chinese fir (Cunninghamia lanceolata) wood treated with dimethyl sulfoxide(DMSO) and diethyl amine, sulfur dioxide and dimethyl sulfoxide mixture (1)EA-SO2-DMSO), and the untreated wood at oven-dried, air-dry and water-saturated states during adsorption and desorption processes were all examined in air or in water. The measurements were carded out at ambient temperature and atmospheric pressure. The load is constant with 62 g or 0.607 6 N. The results obtained were as follows: 1) The instantaneous compliance J0 and the creep compliance J of specimens decrystallized with DEA-SO2-DMSO solution were bigger than those of DMSO swollen wood, and the latter was still much bigger than those of untreated wood. 2) For untreated wood, J0 and J increased with equilibrium moisture content (EMC) of wood, but there was not apparent correlation between wood EMC and the relative compliance. 3) Specimens treated with DMSO and DEA-SO2-DMSO mixture were recrystallized after immersion in water, and the degree ofrecrystallization of the former was larger. 4) For oven-dried specimens, the creep compliances in water were bigger than those in air. But for fiber-saturated and water-saturated specimens they were nearly equivalent to each other. 相似文献
11.
Oblique cutting differs from orthogonal cutting by an inclination given to the knife edge, which induces several changes on
tool geometry, cutting forces, as well as on the quality of machined surfaces. In this work, a pressure bar was used during
oblique cutting to reduce the occurrence of torn grain. The effects of cutting depth, rake angle, and oblique angle on cutting
forces and surface quality were studied. Surface topography, cell damage and wetting properties were used to assess surface
quality. All force components were increased by increasing cutting depth and decreasing rake and oblique angles. The lateral
force, however, increased as the oblique angle increased. The surface roughness increased with increasing the lateral cutting
force. Higher cutting depths and oblique angles tended to provide higher surface roughness, while higher rake angles tended
to reduce surface roughness. The pressure bar was not always able to completely prevent the occurrence of defects when cutting
against the grain. The occurrence of machining defects increased at higher cutting depths and oblique angles. As the rake
angle decreased, the type of machining defect tended to change from torn grain to slight fuzzy grain. Moreover, the best wetting
properties were obtained at lower rake angles, as they induced higher surface roughness. A 25° rake angle, a 30° oblique angle,
and thinner cutting depths should be preferred to reduce dependence on ulterior sanding. 相似文献
12.
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
13.
γ射线辐射杉木压缩木材的固定和蠕变(英文) 总被引：1，自引：0，他引：1
为了探讨木材压缩变定固定的机理 ,该研究对杉木压缩木材进行γ射线辐射处理 ,射线辐射剂量分别为 0 (作为对照试材 ) ,10 3 ,5× 10 3 ,10 4 ,5× 10 4 ,10 5,5× 10 5,10 6,5× 10 6Gy ,然后测定和讨论了γ射线辐射杉木压缩木材的重量损失率、平衡吸湿含水率 (EMC)、吸湿回复率 (RSA)和吸水回复率(RSW )、绝干状态下和吸湿解吸过程中的蠕变。该研究表明 :γ射线的辐射剂量对杉木压缩木材的重量损失率、EMC、RSA、RSW有重要的影响 ,当辐射剂量超过 10 6Gy后 ,试材的重量损失率和EMC显著增大 ,RSA和RSW显著下降 ;另外 ,随着γ射线辐射剂量的增大 ,绝干状态和吸湿解吸过程中杉木压缩木材的瞬时柔量和蠕变柔量均呈增大趋势 .从该研究结果可以推测 ,当γ射线辐射剂量较大时 ,特别当辐射剂量在 5× 10 6Gy左右时 ,杉木压缩木材的细胞壁中发生了降解反应或非结晶化反应 .而且 ,该研究证明了压缩木材细胞壁主成分发生的降解反应能够使木材压缩变定得到一定程度的固定 相似文献
14.
15.
Summary A nonlinear superposition model was developed to assess the load-slip behavior of bolted joints consisting of a single bolt subjected to lateral loading at angles of load to grain. This model characterizes the bolted joint as a pair of orthogonal nonlinear springs aligned parallel and perpendicular to the grain of the wood members. The spring stiffnesses are quantified by a logarithmic or exponential function depending upon whether the connection softens or stiffens with increasing slip. The spring deformations are superimposed to determine the movement of each component of the connection. Deformations of connected members are added vectorially to determine their relative displacement. Spring constant were determined experimentally using metal-to-wood connections. Thick steel side plates were employed to limit the system deformation to the wood component. Wood members were evaluated at angles of load to grain ranging from zero to ninety degrees. Once the spring constants had been determined, the model was executed to predict the load-slip behavior of wood-to-wood connections. These predictions were compared to experimentally obtained load-slip values. The results indicate that the nonlinear superposition concept is a valid approach to predict joint deformation at angles of load to grain.The authors express their gratitude to the Fulbright-Hays Foundation and the Colorado State Agricultural Experiment Station for their financial support of this study 相似文献
16.
D. G. Hunt 《Wood Science and Technology》1989,23(4):323-333
Summary Non-linearity of softwood in axial mechano-sorptive creep during moisture cycling can be characterised as departure from linear behaviour. Linear behaviour is shown by experimental measurement to be a gradual approach to a creep limit with exponentially decreasing increments of compliance, Ji, per moisture cycle, when tested under a constant stress. On the other hand, when the stress is progressively increased by a small increment after each moisture cycle, the compliance increments will progressively increase, having a value of
, where n is the cycle number. By subtracting one compliance increment from the succeeding one, the value of Ji can be obtained. Analysis of experimental results in bending tension and compression showed that the compression test pieces departed from linearity at total strains around 0.14% to 0.15%, the bending test pieces showed slight evidence of non-linearity at about the same strain, whilst the tensile pieces were approximately linear up to 0.18% strain.This project was supported by the U.K. Science and Engineering Research Council and by the European Commission 相似文献
17.
In this report, we undertook studies of the viscoelastic properties of wood from the viewpoint of the fine structure and properties of the constituent materials in the wood cell wall. To measure the mechanical properties of the wood as the behavior of the cell wall, it is required to perform the longitudinal tensile test using a homogeneous specimen. In this study, microtomed specimens of sugi (Cryptomeria japonica D.Don) earlywood were used for the creep test, which were conducted at the fiber saturation point. The substantial creep compliance of the cell wall was simulated using a simplified viscoelastic model consisting of a Voigt element and an independent spring in series. Based on the experimental results, the values of the parameters were optimized. The results were as follows: (1) the longitudinal tensile creep deformation tends to increase with the elapsed time, similar to the bending creep behavior; (2) the magnitude of the longitudinal creep function increases with MFA; and (3) each parameter in the simplified viscoelastic model is markedly affected by the MFA. Based on these results, the mechanism of the longitudinal tensile creep deformation of wood is discussed. 相似文献
18.
The effects of temperature on mechano-sorptive (MS) creep of delignified hinoki wood (Chamaecyparis obtusa Endl.) were investigated using longitudinal (L) and radial (R) specimens during adsorption and desorption over the temperature
range of 20°–80°C. The results were compared with those of stepwise delignified specimens tested at a constant temperature
of 20°C. It was found that the effects of temperature on the MS creep of delignified specimens are more remarkable than for
untreated specimens. The tendencies of increasing MS creep with temperature, delignification, and their combination were observed.
The increase in MS creep for L specimens was relatively small and almost equal in both adsorption and desorption processes,
while for R specimens the MS creep was small in desorption, but significantly different in adsorption. In addition, good correlation
was observed between the MS coefficient (K) and instantaneous compliance (J
0). The increase in MS creep occurs as a result of temperature increase or decrease in lignin content, or their interacting
effects. However, in the case of desorption for R specimens, the increase of MS creep was unexpectedly small due to a remarkably
increased J
0.
Part of this report was presented at the 15th Annual Meeting of the Chubu Branch of the Japan Wood Research Society in Fukui,
October 2005 相似文献
19.
Effects of grain angles of face veneer on surface wave velocities and dynamic shear moduli of wood-based composites 总被引：1，自引：0，他引：1
Yingcheng Hu Tetsuya Nakao Takahisa Nakai Jiyou Gu Fenghu Wang 《Journal of Wood Science》2005,51(3):286-289
The effects of grain angle of face veneer on surface wave velocity and dynamic shear modulus of three types of wood-based composites were examined using a surface wave propagation method. It was found that grain-angle dependence of surface wave velocity and dynamic shear modulus indeed exists for wood-based composites. Grain angles of face veneer were found to have substantial effects on the surface wave velocities and dynamic shear moduli of wood–plastic composite (WP), wood–fiberboard composite (WF), and wood–metal composite (WM). The orthotropic properties of the three composites were defined as the ratio of surface wave velocities at 0° and 90° grain angles (V0/V90), which were 3.7, 2.2, and 2.0 for WP, WF, and WM, respectively. For WP, WF, and WM, the dynamic shear moduli in the 90° grain angle of face veneer were approximately 7%, 19%, and 25% of that in the 0° grain angle, respectively. The relationships between grain angles of face veneer and the shear moduli of the three types of wood-based composites could be represented by Hankinson’s equation, and their optimal n values were 2.1, 1.2, and 1.3 for WP, WF, and WM, respectively.Part of this study was presented at the 15th Annual Meeting of the Chugoku Shikoku Branch of the Japan Wood Research Society, Higashi-Hiroshima, Japan, September 2003 相似文献
20.
Ali Awaludin Watanachai Smittakorn Takuro Hirai Toshiro Hayashikawa 《Journal of Wood Science》2007,53(3):204-210
Empirical equations to determine the bearing strength have been proposed by many researchers and design standards. Because
these equations have been developed mainly based on test results of softwood species, it is a matter of great importance (to
ASEAN structural engineers) to verify the applicability of these equations for tropical hardwood species, which are commonly
used in many ASEAN countries. In this study, wood specimens of Shorea obtusa (a tropical hardwood species) were used and the bearing test under full-hole confi guration was carried out for fi ve different
loading angles to the grain. The bearing stress-embedment curve obtained from the test was approximated by a linear elastic-plastic
diagram indicating the initial and fi nal stiffness of the curve. Testing showed that the average bearing strength parallel
to the grain was 7.25% lower than the prediction given in Eurocode 5. The bearing strength perpendicular to the grain evaluated
based on bearing load at initial cracking was substantially different from any predictions given by previous studies or design
standards. It was also found that the bearing strength and initial stiffness from the bearing stress-embedment curve for loading
at intermediate angles to the grain could be satisfactorily predicted with Hankinson’s formula. 相似文献