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1.
J. Ilic 《Wood Science and Technology》2001,35(1-2):157-166
Dynamic elastic modulus (EL) and wave velocity (V) were determined using resonance vibrations from initially green, 100 × 50 mm sample boards of Eucalyptus regnans F. Muell., and after several stages of drying to oven dry. EL and V were determined from impact induced vibrations and spectral analysis. EL and V from green wood were positively related to basic density and normal shrinkage, only V was negatively related to green
density, and both EL and V were negatively related to green moisture content and the number of internal checks after drying. The latter relationship
has the potential to provide a simple method of segregating highly check prone material. No significant relationships were
obtained with collapse. Outside the hygroscopic range, in low shrinkage material, EL increased little or gradually, while in high shrinkage, collapse prone material, it increased more rapidly, but no clear
breakpoint was evident. In the hygroscopic range, EL increased rapidly in all samples. V increased curvilinearly throughout the entire moisture range, but no difference between
collapse prone and non-collapse prone material was observed.
Received 16 February 1998 相似文献
2.
Julian Moreno Chan John C. Walker Carolyn A. Raymond 《Wood Science and Technology》2011,45(4):609-626
The effects of moisture content from 17 to 159% MC and temperatures from −71°C to +58°C on resonance-based acoustic velocity
and dynamic modulus of elasticity (DMOE) were investigated using 36 boards of radiata pine sapwood. Acoustic velocity decreased
with increasing moisture content and temperature, although effects differed noticeably below and above fibre saturation point
(FSP). Below FSP, acoustic velocity decreased rapidly and linearly with increasing moisture; whereas above FSP changes in
velocity were rather gradual and curvilinear with marked differences in velocity patterns between temperatures below and above
freezing. Acoustic velocity decreased linearly with increasing temperature but there was an abrupt discontinuity at the freezing
point for wood above FSP. Changes in moisture content and temperature affecting wood density and acoustic velocity led to
changes in DMOE, although this relationship was not straightforward because changes of velocity with moisture were linear
or curvilinear and depended on whether wood was frozen or unfrozen, whereas changes of density with moisture content were
invariably linear. For practical work, it is important to estimate the relative effect of changing moisture content or temperature
with respect to standard conditions on DMOE, thus general guidelines were devised to account for significant changes. 相似文献
3.
J. Ilic 《Wood Science and Technology》1999,33(5):425-437
Summary Assessments of internal checking and the physical properties of 124 trees of Eucalyptus regnans F. Muell. have shown that for material dried under relatively mild predryer conditions (30 °C, 65% RH) internal checking
was highly positively correlated with each of collapse, moisture content and normal shrinkage, and weakly negatively correlated
with total external shrinkage. Collapse alone explained 47% of the variation in internal checking. Incidence of internal checking
in sample boards could be estimated with moderate success by each of the following properties measured on board ends: collapse,
the number of internal checks and initial moisture content. Material with high mean basic density above 530 kg/m3 was associated with low levels of internal checking and collapse. However, the maximum naturally occurring density of E. regnans was not high enough to obviate collapse and internal checking. It was observed that growth rings in 100 × 50 mm backsawn
boards in which the earlywood air-dry density was below 450 kg/m3 showed internal checking. The size and number of internal checks increased with a decrease in earlywood density. It was shown
that drying E. regnans below temperatures of 24–30 °C does not eliminate collapse, thus raising doubt about the validity of a temperature threshold
concept in that range.
Received 17 September 1997 相似文献
4.
Hot-pressing is the main process in flakeboard manufacture. Studies in this field also emphasize the effect on the heat-transfer
process of the following factors: hot-pressing temperature, original moisture content (MC), target thickness and target density.
In this experiment, dynamic data of changes in temperature in mats can be logged through temperature transducers and a computer
data log system. The results of the experiment indicate that the core temperature-time curve can be divided into three stages:
a stage of a rapidly rising temperature, a stage of moisture vaporizing and a stage of a slowly increasing temperature. If
the hot-pressing temperature or the original MC increases during the first stage, the temperature will increase at an accelerated
rate. This rate of acceleration in thin or low-density boards is very high. During the second stage, increasing the hot-pressing
temperature or decreasing the original MC can shorten the time used to vaporize moisture. In thin or low-density board, this
time period is short. In the third stage the original MC does not affect the rate of temperature increase, while the effect
of the other factors is the same as that at the first stage. Given different conditions, vaporization temperature in the mat
changes.
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Translated from Journal of Beijing Forestry University, 2005, 27(2): 92–95 [译自: 北京林业大学学报, 2005, 27(2): 92–95] 相似文献
5.
Matched sample boards from 20 quarter-sawn boards of Victorian Ash (Eucalyptus regnans F. Muell and E. delegatensis R.T. Baker) were dried using three different levels of ramped pre-drying schedules to investigate the effects of moisture
gradients on collapse recovery and internal checking. Prior to reconditioning, most wet cores were found in highly collapsed
boards with low density. Reducing the gradients in these boards is crucial for recovering collapse and closing internal checks.
If time allows the boards to be equilibrated prior to steam reconditioning, a target mean moisture content of ≤20% with a
moisture gradient of close to 5% (core to surface moisture content) is likely to recover slightly more collapse than targeting
a mean moisture content close to ≥15%. However, if time or kiln restraints limit equilibration it is likely to be better to
target a percentage moisture content of closer to 15% in order to ensure that the core to surface moisture gradients are below
8–10%. The slight reduction in collapse recovery with this second approach is less important than the possibility that collapse
and internal checks in the centre of boards with wet cores will not be closed. Care needs to be used with this latter approach
not to over-dry some boards, since moisture contents below 15% will progressively reduce collapse recovery. For boards within
these moisture content guidelines, the application of heat, rather than moisture pick-up, appears to be the most important
component of the steaming reconditioning process. Hence, steaming only needs to be undertaken for long enough to heat the
core of the board close to the target temperature of 100°C. A simple method for estimating this heat-up time for different
thicknesses and species was demonstrated based on a key dimensionless group for heat transfer, the heat-transfer Fourier number. 相似文献
6.
On the loss factor of wood during radio frequency heating 总被引:2,自引:0,他引:2
The radial direction loss factor of full-size western hemlock sapwood and heartwood, as well as western red cedar heartwood
timbers was measured using the direct calorimetric method with a laboratory-scale radio frequency/vacuum dryer at the frequency
of 13.56 MHz, moisture content range between 10 and 80%, temperature range between 25 and 55 °C, and root mean square (rms)
electrode voltages of 0.8 and 1.1 kV, respectively.
The results indicated that the moisture content, temperature, electric field strength and wood type significantly affected
the loss factor. Empirical regression equations were derived based on the experimental data that made possible the calculation
of the loss factor and power density within wood during RF heating.
Received 18 January 1997 相似文献
7.
Experimental determination of the convective heat and mass transfer coefficients for wood drying 总被引:1,自引:1,他引:0
The knowledge of the convective heat and mass transfer coefficients is required for the characterization of the boundary
conditions of the heat and mass transfer equations of a wood drying model based on water potential. A new experimental method
for the determination of the convective mass transfer coefficient is presented. This method is based on the measurement of
the moisture content, and indirectly the water potential, at the surface of a wood specimen at different drying times. Drying
experiments were performed on red pine (Pinus resinosa Ait.) sapwood from nearly saturated to dry conditions at 56 °C, 52% relative humidity and air velocities of 1.0, 2.5 and
5.0 m s−1. The results show that the convective mass transfer coefficient is constant until the wood surface moisture content reaches
about 80% and then decreases more or less gradually as the moisture content decreases further. The convective mass transfer
coefficient increases with air velocity. A regression analysis shows that there is no significant improvement in considering
the water potential gradient near the wood surface when the difference in water potential between the surface and the surrounding
air (ψs − ψ∞) is used to determine the convective mass flux at the surface. Also, ψs − ψ∞ is more appropriate than the water vapour pressure difference (pvs − pv∞) as the responsible driving force of the moisture flux leaving the wood surface. The convective heat transfer coefficient
was determined during the same experiments. A plateau is observed at high values of moisture content corresponding to the
constant drying rate period.
Received 27 February 1998 相似文献
8.
Steam conditioning of softwood boards after kiln drying is of critical importance for relief of residual drying stresses
and to improve distribution of final moisture content. The conditioning practice in New Zealand includes two steps: immediately
after high temperature (HT) drying the load is cooled until the core wood temperature is 75 to 90°C, and then the stack is
steam conditioned for a period of 1 to 4 hours depending on the lumber thickness and moisture content after drying. In this
work, experimental and theoretical studies were performed to better understand the conditioning process and to investigate
factors which influence its effectiveness. In the experiment, 50 mm thick Pinus radiata sapwood boards were first dried at 120/70°C for 11, 12, 13, 16 and 18 hours, respectively, to varying moisture contents,
and then cooled and steam conditioned for 1 hour. To assess the effectiveness of conditioning, moisture pick-up, moisture
gradient, and transverse residual drying stress (indicated by cup and strain) were measured. It was found that drying wood
to a low moisture content (below 6%) increased the conditioning effectiveness. A separate matched stack was conditioned for
4 hours after 13 hours drying which showed better results than 1 hour conditioning. A mathematical model for wood drying was
extended to include both the cooling and conditioning phases. The model was numerically solved to examine the wood temperature
and moisture content changes during the whole process of drying, cooling and final steam conditioning. Increase in wood temperature,
moisture pickup and moisture gradient during steam conditioning were predicted and validated by the experimental data. This
information is currently being used at the New Zealand Forest Research Institute in simulation of stress development and relief
for drying of Pinus radiata lumber.
Received 6 July 1998 相似文献
9.
On the measurement of formaldehyde release from low-emission wood-based panels using the perforator method 总被引:1,自引:1,他引:0
In Europe, the perforator method (EN 120) is the mostly used laboratory method of the wood-based panel industry. Usually,
the measured perforator value depends on the moisture content of the boards. According to DIBt-100, the measured perforator
values are corrected to a common moisture content (MC) of 6.5% using an established equation proposed by Jann and Deppe (1990). The correction factor of Jann and Deppe (1990) is based on the assumption that particle- and fibreboards change their perforator values to the same extent regardless whether
increasing or decreasing the moisture content in the range of 3 ≤ u ≤ 9%. Application of this correction factor to particle- and fibreboards of higher moisture content than 6.5% can lead to
biased corrected results in favour of low emission. The corrected values can also lead to paradoxical relation between the
perforator values and emission in the low-emission region. 相似文献
10.
A. Negi 《Wood Science and Technology》1999,33(3):209-214
Small compressive stresses (500 N, 1000 N, 2000 N) of small duration were exerted on 2 × 2 × 2 cm3 wood specimen of Eucalyptus hybrid. Two relative humidity levels of 93% RH and 27% RH were maintained in dessicators. The
per‐cent change in Equilibrium Moisture Content (EMC) was measured. It was found that the initial percent change of EMC was
2.62 times higher in low moisture content specimens when compared to the higher moisture content specimens. The EMC was found
to decrease on applying compressive stress irrespective of the stress level. An explanation for this effect in terms of re-alignment
of hydrogen bonds is presented in this paper.
Received 8 December 1997 相似文献
11.
We conducted creep tests to evaluate creep behaviors of conventional Japanese framing (jikugumi) structures as reported in a previous article. We measured beam deflections of two structures: one of them was composed of
only green timbers (G) and the other with only kiln-dried timbers (D). Besides the two structures, we prepared green and kiln-dried
beams to measure moisture content (MC), weight, and dynamic Young’s modulus (E
f) by the longitudinal vibration method. We attempted to predict deflections of beams in the structures by using experimental
data for single beam specimens. The proposed simple predictive model was derived from two equations: a relation between MC
and equilibrium moisture content calculated with temperature and relative humidity, and a relation between MC change and relative
deflection change. Beam deflections were traced for 2.5 years, while the predictions were based on experimental data from
loading to the 11th day of the test. It was assumed that sensitivity of deflection change to MC should differ during desorption
or adsorption. Although annual cyclic changes were observed in E
f, there was no obvious relationship between E
f and beam deflection.
Part of this article was presented at the Annual Meeting of the Architectural Institute of Japan, Kyushu, September 1998 相似文献
12.
Marek Gnatowski Rebecca Ibach Mathew Leung Grace Sun 《Wood material science & engineering》2015,10(1):94-111
AbstractTwo wood plastic composite (WPC) boards, one experimental and one commercial, were exposed to exterior conditions and evaluated non-destructively using a clinical magnetic resonance imaging (MRI) unit for moisture content (MC) and distribution. The experimental board was exposed in Vancouver, British Columbia, for more than 8 years, and the commercial board was exposed near Hilo, Hawaii, for 2 years. Both boards were characterized in terms of wood content, density, water uptake properties and voids content. The experimental board was additionally destructively analysed for water absorption of the WPC and MC calculated based on the wood content for verification of MRI results. MRI detected the presence of free water and its distribution in both of the WPC boards. Fibre saturation in the experimental board was found to be about 22–24%, in comparison to 25–30% present in most wood species. There was good correlation between the detection of free water by MRI and by destructive testing. Magnetic resonance images showed various major points of water entry in the WPC boards such as the support area, the cut ends, the dripping edge and the sides of the boards. For the experimental board, significant water entry also occurred at the upper exposed surface. 相似文献
13.
Dynamic properties of bamboo, Phyllostachys pubescens, with moisture content (MC) ranging from −130 to 130°C, were studied by dynamic mechanical analysis (DMA). The results showed
that the hygrothermal effect on dynamic mechanical properties was negative. The storage modulus decreases with increasing
temperature and MC, and glass transition temperature decreases with increasing MC. The glass transition temperature and tan
delta of bamboo were 30.5°C, 0.02 and 10.61°C, 0.04, when MC was 10% and 34%, respectively.
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Translated from Journal of Nanjing Forestry University (Natural Sciences Edition), 2006, 30(1): 65–68 [译自: 南京林业大学学报(自然科学版), 2006, 30(1): 65–68] 相似文献
14.
共振板振动特性与钢琴声学品质主观评价的关系 总被引:2,自引:1,他引:1
选取俄罗斯远东红皮云杉、东北长白鱼鳞云杉、西藏林芝云杉、美国西加云杉4个树种的试件,每树种2块共制作8块共振板,采用基于打击音的快速傅里叶变换(FFT)频谱方法分析共振板的振动特性,计算得出共振板不同方向的动态弹性模量、纵波传播速度、共振板边部剩余试件动弹性模量及共振板制作钢琴后的振动传播响应时间.利用共振板制作成试验用钢琴后,采用专家主观评价的方式对钢琴的声学品质进行评价.通过分析共振板振动特性参数与钢琴声学品质主观评价得分之间的关系得出,共振板y方向的振动特性参数与钢琴声学品质主观评价得分项目之间呈一定程度或显著的线性相关,而x方向的振动特性参数与主观评价得分项目之间的相关关系明显弱于y方向.因此,通过改善共振板y方向的振动特性可显著提高钢琴的声学品质,也说明了共振板y方向的振动特性参数检测对于钢琴声学品质评价的重要性.共振板y方向的振动特性参数与钢琴声学品质主观评价得分之间的相关性大于x方向的相关性,这一规律与音板上高、中音区域的琴弦排列和音板的y方向接近平行、低音区域琴弦排列及y方向的夹角小于x方向的结构特点有关. 相似文献
15.
Ken Watanabe Isao Kobayashi Naohiro Kuroda Masaki Harada Shuichi Noshiro 《Journal of Wood Science》2012,58(5):383-390
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. 相似文献
16.
Mohammad Derikvand Nathan Kotlarewski Michael Lee Hui Jiao Gregory Nolan 《Wood material science & engineering》2020,15(3):172-181
ABSTRACTThe main goal of this study was to investigate the visual characteristics, recovery rate, and flexural properties of sawn boards from a fibre-managed plantation Eucalyptus globulus resource as a potential raw material for structural building applications. The impacts of the visual characteristics, strength-reducing features, and variation in basic density and moisture content on the bending modulus of elasticity (MOE) and modulus of rupture (MOR) of the boards were investigated. The reliabilities of different non-destructive methods in predicting MOE and MOR of the boards were evaluated, including log acoustic wave velocity measurement and numerical modellings. The MOE and MOR of the boards were significantly affected by the slope of grain, percentage of clear wood, and total number of knots in the loading zone of the boards. The normal variation in basic density significantly influenced the MOE of the boards while its effect on the MOR was insignificant. The numerical models developed using the artificial neural network (ANN) showed better accuracies in predicting the MOE and MOR of the boards than traditional multi-regression modelling and log acoustic wave velocity measurement. The ANN models developed in this study showed more than 78.5% and 79.9% success in predicting the adjusted MOE and MOR of the boards, respectively. 相似文献
17.
Wood exhibits a pronounced time dependent deformation behavior which is usually split into ‘viscoelastic’ creep at constant
moisture content (MC) and ‘mechano-sorptive’ creep in varying MC conditions. Experimental determination of model rheological
parameters on a material level remains a serious challenge, and diversity of experimental methods makes published results
difficult to compare. In this study, a cantilever experimental setup is proposed for creep tests because of its close analogy
with the mechanical behavior of wood during drying. Creep measurements were conducted at different load levels (LL) under
controlled temperature and humidity conditions. Radial specimens of white spruce wood [Picea glauca (Moench.) Voss.] with dimensions of 110 mm in length (R), 25 mm in width (T), and 7 mm in thickness (L) were used. The influence of LL and MC on creep behavior of wood was exhibited. In constant MC conditions, no significant
difference was observed between creep of tensile and compressive faces of wood cantilever. For load not greater than 50% of
the ultimate load, the material exhibited a linear viscoelastic creep behavior at the three equilibrium moisture contents
considered in the study. The mechano-sorptive creep after the first sorption phase was several times greater than creep at
constant moisture conditions. Experimental data were fitted with numerical simulation of the global rheological model developed
by authors for rheological parameter identification. 相似文献
18.
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
19.
Rohny Setiawan Maail Kenji Umemura Hideo Aizawa Shuichi Kawai 《Journal of Wood Science》2012,58(1):31-37
This study examined the effects of moisture content (MC) on the manufacture of cement-bonded particleboard (CBP) using supercritical
CO2 in the curing process. Significant correlations were found between MC and the performance of CBP: the internal bond strength,
modulus of rupture, and modulus of elasticity values of CBP achieved their maximums, when the MC of boards was approximately
30%. This finding indicated that during the curing phase of manufacturing CBP, a MC of about 30%, which is nearly equal to
the water–cement (w/c) ratio of about 0.34, contributes to improved mechanical properties. However, the mechanical properties
decreased when the MC was below 30%, which had a negative effect on board performance, indicating that carbon dioxide could
not fully react and no carbonation occurred during the curing process. Maintaining a MC of approximately 30% as an ordinary
condition of the cement required in the curing of CBP could promote the reaction of carbon dioxide to form calcium carbonate
(CaCO3), which leads to increased final strength of CBP. Both X-ray diffractometry and thermal gravimetry observation agreed well
with these results and clarified that the increase of CaCO3 content caused by carbonation with increased MC of boards contributed to improving the mechanical properties of CBP. 相似文献
20.
G. Vázquez G. Antorrena J. González S. Freire I. Crespo 《Wood Science and Technology》2000,34(4):345-354
Eucalyptus globulus wood was subjected first to HCl–catalysed delignification with 70% acetic acid under conditions realizing an incomplete 3 × 3 × 3
factorial design (HCl concentration 0, 0.025 or 0.05%; temperature 120, 140 or 160 °C; reaction time 1, 2.5 or 4 h), and then
to enzymatic hydrolysis. The hydrolysis kinetics conformed to both Ghose's empirical model and a biexponential equation. The
biexponential fit implies the presence of both readily and reluctantly hydrolysed cellulose fractions, and the fitted coefficients
show hydrolysis yield to depend largely on the digestibility of the latter. Multiple regression of performance variables on
pulping conditions showed that neither the rate nor the extent of hydrolysis is greatest for pulps with minimum lignin or
xylose contents; we attribute this circumstance to the condensation and precipitation of lignin under severe pulping conditions,
which protects the cellulose of the pulp from enzymatic attack.
Received 20 June 1998 相似文献