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1.
Summary The mechanical behaviour of three species of hardwoods soaked in different swelling liquids, compressed at high rates of strain, was investigated using a split Hopkinson pressure bar system. Variations in elastic moduli, proportional limit and maximum stress with respect to the treatments were studied. It was found that the saturated specimens could be as stiff as the dry ones. This result was explained by the behaviour of the liquid present in the large cavities of the wood, i.e. the lumens of the cells, which must be different from that observed at low rates of strain. At large rates of strain, this liquid cannot flow out of the pores and must behave like a solid; therefore the structure of the material is reinforced and, as a consequence, the softening effect of the soaking agent can be masked.  相似文献   

2.
During refining of mechanical pulp, a process occurring at high speed at temperatures of 140–160°C, the flexibility and bonding ability of wood fibres are increased. To understand the mechanical behaviour of the fibres in this operation, deformations at low speed of wet wood specimens at 50°C were studied under two different combinations of shear and compression loadings. The results were compared with the behaviour of wet wood in pure compression. Some features of the deformation that occurred in earlywood were analysed using an image analysis procedure. During pure compression the cell walls bend independently of the shape of the fibre cells and their cell wall thickness. Under combined shear and compression, however, mainly the corners of the fibre cells get deformed. In a second deformation performed in compression, the fibre cells follow the same deformation pattern as given by the first deformation type whether in compression or in combined shear and compression. The interpretation was that permanent defects in the cells themselves were introduced already in the first load cycle of the wood samples. The load combination with lower shear gave the same permanent strain as the case of pure compression but using less energy.  相似文献   

3.
Summary The incidence of non-linearity with stress in the rheological behaviour of wood in bending was shown earlier to occur at an unexpectedly low stress. This has been further confirmed by the study of an additional species, alpine ash.Tests on hoop pine, one of the species previously studied in bending, have shown that in compression, non-linearity first occurs at stresses which are a much higher fraction of the ultimate stress than in bending, but in approximately the same range of actual stress. This suggests that the cause of non-linearity at such a low stress in bending lies in the fact that the compressive strength is considerably lower than the bending strength. The stress on the compression face of a beam reaches a high percentage of the ultimate compressive strength by the time the bending stress reaches the limit of proportionality in bending and the nonlinear effects in a beam are attributable mainly to stresses near the compression face.A marked effect of temperature on fractional total creep for hoop pine in compression was found even within the range 20 to 50° C, the creep increasing by a factor of about 2.5 in this range.The authors wish to thank Miss N. Ditchburne of the Division of Mathematical Statistics, C.S.I.R.O., for statistical advice and for carrying out statistical computations, and Mr. L. D. Armstrong for valuable discussion and suggestions.  相似文献   

4.
We investigated the feasibility of using several fast-growing tropical or subtropical hardwood species for timber production by measuring key wood qualities in relationship to the high rates of lateral growth. The trees tested were sampled from even-aged plantations of Acacia mangium, A. auriculiformis, hybrid Acacia (A. mangium × A. auriculiformis), Eucalyptus grandis, E. globulus, and Paraserianthes falcataria (Solomon and Java origin) that had already reached commercial harvesting age. The released strain of the surface growth stress (RS), xylem density (XD), microfibril angle (MFA), and fiber length (FL) were measured at the outermost part of the xylem at breast height in each tree. Results were then compared to the lateral growth rate (radius/age) at breast height, which provides a relative indicator of the amount of tree growth per year. Our findings indicated that RS was constant, regardless of lateral growth rate in each species. Similar results were observed for XD, MFA, and FL, with a few exceptions, suggesting that high growth rates do not intrinsically affect the wood properties of fast-growing tropical or subtropical species that have reached harvesting age. However, special attention must be paid to patterns of xylem maturation when developing plantations of such species.  相似文献   

5.
In order to investigate the way in which fibre properties affect the mechano-sorptive creep phenomenon in paper, single wood fibres were exposed to tensile stresses at a constant humidity of 80% relative humidity (RH) and in a cyclic humidity environment varying between 80 and 30% RH. Contrary to earlier claims, it was demonstrated that single wood fibres exposed to a cyclic RH show a considerably higher creep than that corresponding to the highest RH experienced in the cycle, i.e., a mechano-sorptive behaviour. The creep strain rate at cyclic humidity was shown to be a function of the creep rate at constant climate, and to be an apparent linear function of the applied stress.  相似文献   

6.
The dynamic water vapour sorption properties of Scots pine (Pinus sylvestris L.) wood samples were studied to investigate the modifying effects of glutaraldehyde. Pine sapwood was treated with solutions of glutaraldehyde and a catalyst (magnesium chloride) to obtain weight per cent gains of 0.5, 8.6, 15.5, and 21.0%, respectively. The sorption behaviour of untreated and treated wood was measured using a Dynamic Vapour Sorption apparatus. The results showed considerable reduction in equilibrium moisture content of wood and the corresponding equilibrium time at each target relative humidity (RH) due to glutaraldehyde treatment. The moisture adsorption and desorption rates of modified and unmodified wood were generally faster in the low RH range (up to approximate 20%) than in the high range. Modification primarily reduced the adsorption and desorption rates over the high RH range of 20–95%. Glutaraldehyde modification resulted in a reduction in sorption hysteresis due to the loss of elasticity of cell walls.  相似文献   

7.
The kinetics of heat treatment as well as its effect on some physical and mechanical properties of poplar wood (Populus alba L.) were analysed in this research. Kinetic tests were performed at different treatment temperatures and two different air ventilation settings [low and high air exchange rate (AER) with the exterior]. The treatment kinetics was studied, starting from the oven-dry condition, according to the mass loss during time. The time–temperature equivalency was checked, the mass loss versus time formalised through a master curve. The analysis clearly showed how the heat treatment at low and high AER presents different degradation kinetics even if similar activation energy values were found. Some physical and mechanical properties of wood after treatments up to a mass loss of 7 and 10 % starting from oven-dry or standard environmental conditions state were also studied. All of the treated samples showed statistically significant differences compared to the untreated one. The treatments performed at 7 or 10 % of dry mass loss showed homogeneous behaviour. The same tendency was observed for the treatments starting at oven-dry or standard environmental conditions with the exception of Young’s modulus, which resulted in smaller reductions in wet starting condition when compared to dry samples.  相似文献   

8.
In this study, longitudinal cyclic tensile tests were performed on green wood samples of Populus cv I4551. Complex mechanical behaviour, such as permanent set in terms of displacement and strain-dependent stiffness, was found. A linear relationship between stiffness and strain enabled each sample to be characterized. A large-scale experimental campaign led to the observation of the evolution of temporal and spatial intra-ring mechanical behaviour of intra-ring sliced specimens during wood maturation and tree gravitropic response. The results showed that tension wood lamellas exhibit strain hardening behaviour whereas normal wood lamellas exhibit strain softening behaviour. Temporal variations in the strain hardening behaviour of tension wood lamellas occurred once cell wall deposition was achieved. Moreover, no correlation was found between infradensity and mechanical behaviour of lamellas. These results show that cells undergo temporal variations in their properties due to a complex maturation process.  相似文献   

9.
THE EFFECT OF HEAT TREATMENT ON DIFFERENT SPECIES WOOD COLOUR   总被引：2，自引：0，他引：2  
Woodisnaturalmaterial,naturegivewoodsurfacecolor,g]oss,grain,qualitysenseetc-,whichconsititutedwoodaesthet-icfeeling.Forthisreson,peoplealwaysusedwide]ywoodtomakefurnitureanddecorating,andstlldiedonthequntitativetestingofwoodsurfacevisualphysicalmagnitude.tl-8jTreeswereprocessedoperationbyaseriesofworkingprocesstoformthewoodsurfacewhichwesawandtouchedonfur-nitureanddecorating.Inthesekindsofworkingprocess,whetherthevisualphysi-calmagnitudeofwoodsurfacehadvaria-tionsorthisvariationschangedwoodna…  相似文献   

10.
Two-body and three-body abrasive wear tests of katsura wood were carried out using abrasive paper and moving abrasive grains, respectively. The two-body and three-body abrasive wear properties were investigated and compared. The wear rate of two-body abrasive wear was two orders of magnitude larger than that of three-body abrasive wear. Moreover, two-body abrasive wear of katsura wood increased with higher applied surface pressure, whereas three-body abrasive wear did not always depend on the applied surface pressure. Based on these results and observation of the wear surface profiles, it is suggested that two-body abrasive wear is more affected by yield stress and surface microstructure, and three-body abrasive wear is more affected by the cutting action of moving abrasive grains. Furthermore, during wear tests with different abrasive grain sizes, critical grain size effects of two-body abrasive wear were observed at low applied surface pressures but not at high applied surface pressures. The critical grain size effects of three-body abrasive wear were observed at both low and high applied surface pressures.Part of this report was presented at the 49th Annual Meeting of the Japan Wood Research Society, Tokyo, April 1999  相似文献   

11.
Simulated organic waste was biodegraded in a laboratory-scale machine using matrices prepared from four wood species to investigate the effects of wood species on the degradation rate and the bacterial community. The degradation rate, estimated by measuring weight loss and CO2 evolution, was found to be equal among the four wood species. Changes in viable cell counts and microbial communities over time were examined. Viable cell counts were also similar among the wood species, but initial bacterial communities differed owing to differences in wood species, although these communities became similar with time. The sensitivity of isolates to wood extractives was examined using paper discs. The extractive-insensitive bacteria species were dominant at the initial stage of biodegradation. However, occupancy of sensitive bacteria increased with time. It was thought that antibacterial extractives were degraded or inactivated after some time.Part of this report was presented at the 50th annual meeting of the Japan Wood Research Society, Kyoto. Japan, April 2000  相似文献   

12.
On the fracture morphology in wood   总被引：5，自引：0，他引：5  
Summary Structural changes in spruce and aspen wood samples subjected to axial compression were examined by means of the scanning electron microscope. For comparison, macroscopic model experiments were carried out on tube-shaped samples made of paper so as to represent segments of fibriform xylem cells. The results show that there are fracture patterns characteristic of wood in general and others characteristic of the species of wood. The phenomena characteristic of wood in general are prevalent at the cellular level and in the fracture behaviour of the cell wall layers and perforations. The characteristics of the various species of wood dominate at the level of the growth rings and are decisively influenced by the composition and arrangement of the tissues. The model experiments show that the failure morphology of the individual cells of the xylem may be explained to some extent by their geometry.  相似文献   

13.
This study is focused on what factor mainly affects the mechanical properties of each wood species in the lateral direction. At first, the influence of the density which is closely related to mechanical properties in the longitudinal direction was also researched in the lateral direction. Thus, the elastic modulus, strength, and failure strain in the lateral tension were measured using thin cross-sectional samples of softwoods and hardwoods, having wide varieties in the density and anatomical features. The results obtained are as follows. The linear relationship between the density and the elastic modulus which has been verified in the longitudinal direction was not observed in the lateral tension for the samples with the annual ring inclination of 90°, which samples were influenced by ray arranged parallel to the tensile direction. However, samples with the annual ring inclination of 45° showed the high correlation between the density and the elastic modulus due to the shearing deformation of the cell shape. On the other hand, the proportional relationship between the elastic modulus and strength which has been verified in the longitudinal direction was not observed in the lateral tension except for the samples with the annual ring inclination of 90°. From the results obtained, it was revealed that the mechanical properties of wood in the lateral direction were significantly affected not only by the density but also by the structural features such as deformation of cell shapes, arrangement of ray or vessels, and the degree of the transition from the earlywood to the latewood.  相似文献   

14.
We investigated whether timing and rate of growth are related to the life strategies and fitness of three conifer species. Intra-annual dynamics of wood formation, shoot elongation and needle phenology were monitored over 3 years in five Norway spruces (Picea abies (L.) Karst.), five Scots pines (Pinus sylvestris L.) and five silver firs (Abies alba Mill.) grown intermixed. For the three species, the growing season (delimited by cambial activity onset and cessation) lasted about 4 months, while the whole process of wood formation lasted 5-6 months. Needle unfolding and shoot elongation followed the onset of cambial activity and lasted only one-third of the season. Pines exhibited an 'extensive strategy' of cambial activity, with long durations but low growth rates, while firs and spruces adopted an 'intensive strategy' with shorter durations but higher growth rates. We estimated that about 75% of the annual radial increment variability was attributable to the rate of cell production, and only 25% to its duration. Cambial activity rates culminated at the same time for the three species, whereas shoot elongation reached its maximal rate earlier in pines. Results show that species-specific life strategies are recognizable through functional traits of intra-annual growth dynamics. The opposition between Scots pine extensive strategy and silver fir and Norway spruce intensive strategy supports the theory that pioneer species are greater resource expenders and develop riskier life strategies to capture resources, while shade-tolerant species utilize resources more efficiently and develop safer life strategies. Despite different strategies, synchronicity of the maximal rates of cambial activity suggests a strong functional convergence between co-existing conifer species, resulting in head-on competition for resources.  相似文献   

15.
In this study the thermoplastic flow behavior of steamed wood flour was investigated. First it was demonstrated that steamed Japanese beech flour flowed out of the nozzle under compression at high temperature in a thermal flow test with a capillary rheometer. The effects of the steaming temperature, steaming time, compressive pressure, and moisture content of wood flour on the thermal flow temperature were examined. It was shown that the higher the steaming temperature and compressive pressure, the lower the thermal flow temperature. Also, the thermal flow temperature of the sample steamed at 200°C for 20 min became lowest and increasingly higher over time. Furthermore, the thermal flow temperature became linearly low with increasing moisture content of the sample under 15%, whereas it became essentially constant over 15%. It is clarified that compressive pressure and moisture content as well as the steaming conditions profoundly affect the thermoplastic flow behavior of steamed wood flour.  相似文献   

16.
This paper describes an experimental device designed to determine the mechanical behaviour of lignocellulosic products subjected to high strain rates. This impact system consists of a moving trolley equipped with an accelerometer, which is thrown against a fixed trolley. The sample is attached to the fixed trolley, and the accelerations of both trolleys during the impact are analysed to obtain stress/strain curves. A high-speed camera synchronised with a high-powered xenon flash records up to 4,000 frames/s. A set of tests on wood samples is described to illustrate the potential of this new device. In particular, the cross-effects of compression rate and moisture content were demonstrated by performing both quasi-static (1 mm min?1 using a conventional testing machine) and dynamic tests (1.7 m s?1 using the impact device). Poplar and spruce samples, equilibrated at three different moisture contents (air-dried, fibre saturation point (FSP) and fully saturated), were tested. Two findings are particularly worthy of mentioning: (1) despite the plasticising role of water, the sample at FSP exhibited a fragile behaviour at the high compression rate, (2) the resistance due to the expulsion of water out of saturated samples can be assessed only by performing an impact test.  相似文献   

17.
Chemical composition of Norway spruce and pine, two softwood species, has been investigated by X-ray Photoelectron Spectroscopy (XPS). Contrary to results previously obtained with beech wood, which allow to obtain information on bulk chemical composition from surface composition analysis, XPS analysis appears to be unsuitable for the characterisation of Norway spruce and pine wood chemical composition. Indeed, chemical compositions calculated from XPS data differ strongly from those obtained from microanalyses which are in good agreement with theoretical composition described in the literature. XPS analysis of both the softwood surfaces indicated high carbon contents explained by migration of lipophilic extractives to the surface under the influence of the vacuum necessary for XPS analysis. Nonvolatile extractives contained in wood were extracted and deposited on glass plates and analysed. Survey and detailed C1s spectra indicated similar signals to those recorded on wood surfaces. This phenomenon was not observed when samples had been previously extracted before analysis. These results strongly evidenced that extractives present in both species are able to migrate through resin canals from the bulk of the sample to the surface when put into ultra high vacuum. XPS presents, therefore, some limits in the case of the analysis of softwood species containing extractives able to migrate to the surface during analysis. This behaviour, difficult to control, could lead to erroneous interpretations due to extractives enrichment of the surface under the effect of vacuum.  相似文献   

18.
I tested the presence of rapid and delayed induced resistance in Pinus sylvestris L. by biotests, rearing three species of diprionid sawflies on defoliated and undefoliated trees. I damaged the pines artificially by cutting mature needles with scissors at the beginning of the growing season. Four levels of defoliation were created on the basis of levels of removed needle biomass. Sawfly larval and cocoon weights were retarded and relative growth rates delayed as a result of an increase in damage level. The larval periods were prolonged at most 2–6 days. The response to the damage was partly species‐specific. The needle water content decreased in the following growing season in connection with low and moderate damage and increased at high damage levels. The nutrient contents of the foliage in the damaged and undamaged trees did not differ significantly. The Scots pine showed damage‐induced changes in food quality after extensive defoliation, which affected, via plant, species using the same host.  相似文献   

19.
The effect of aging on lignins of wood   总被引：1，自引：0，他引：1  
Summary Samples of different wood species varying in age from 900 to 4400 years and stored during this period under different conditions were analyzed for their lignin content. Lignins isolated from the samples were investigated by IR-spectroscopy. It could be shown that lignin in wood undergoes oxidative changes which lead to a decrease in the amount of lignin isolated by the hydrochloric acid procedure. at Hamburg-Lohbrügge.DAAD Visiting Professor Fellowship to study and do research at the Bundesforschungsanstalt für Forst- und Holzwirtschaft at Hamburg-Lohbrügge.Dedicated to Karl Kratzl on the occasion of his 60th anniversary  相似文献   

20.
Leaves and samples of recent wood of Eucalyptus species were collected along a rainfall gradient parallel to the coast of Western Australia between Perth in the north and Walpole in the south and along a southwest to northeast transect from Walpole in southwestern Australia, to near Mount Olga in central Australia. The collection included 65 species of Eucalyptus sampled at 73 sites and many of the species were collected at several sites along the rainfall gradient. Specific leaf area (SLA) and isotopic ratio of 13C to 12C (delta 13C) of leaves that grew in 2002, and tree ring growth and delta 13C of individual cell layers of the wood were measured. Rainfall data were obtained from the Australian Bureau of Meteorology for 29 locations that represented one or a few closely located collection sites. Site-averaged data and species-specific values of delta 13C decreased with decreasing annual rainfall between 1200 and 300 mm at a rate of 1.63 per thousand per 1000 mm decrease in rainfall. Responses became variable in the low rainfall region (< 300 mm), with some species showing decreasing delta 13C with rainfall, whereas delta 13C increased or remained constant in other species. The range of delta 13C values in the low rainfall region was as large as the range observed at sites receiving > 300 mm of annual rainfall. Specific leaf area varied between 2 and 6 m2 kg(-1) and tended to increase with decreasing annual rainfall in some species, but not all, whereas delta 13C decreased with SLA. The relationship between delta 13C and SLA was highly species and soil-type specific. Leaf-area-based nitrogen (N) content varied between 2 and almost 6 g m(-2) and decreased with rainfall. Thus, thicker leaves were associated with higher N content and this compensated for the effect of drought on delta 13C. Nitrogen content was also related to soil type and species identity. Based on a linear mixed model, statistical analysis of the whole data set showed that 27% of the variation in delta 13C was associated with changes in SLA, 16% with soil type and only 1% with rainfall. Additionally, 21% was associated with species identity. For a subset of sites with > 300 mm rainfall, 43% of the variation was explained by SLA, 13% by soil type and only 3% by rainfall. The species effect decreased to 9% because there were fewer species in the subset of sites. The small effect of rainfall on delta 13C was further supported by a path analysis that yielded a standardized path coefficient of 0.38 for the effect of rainfall on SLA and -0.50 for the effect of SLA on delta 13C, but an insignificantly low standardized path coefficient of -0.05 for the direct effect of rainfall on delta 13C. Thus, in contrast to our hypothesis that delta 13C decreases with rainfall independent of soil type and species, we detected no statistically significant relationship between rainfall and delta 13C in leaves of trees growing at sites receiving < 300 mm of rainfall annually. Rainfall affected delta 13C indirectly through soil type (a surrogate for water-holding capacity) across the rainfall gradient. Annual tree rings are not clearly visible in evergreen Eucalyptus species, even in the seasonally cool climate of SW Australia. Generally, visible density transitions in the wood are related not to a strict annual cycle but to periods of growth associated mainly with rainfall. The relationship between delta 13C of leaves and the width of these stem increments was not statistically significant. Analysis of stem growth periods showed that delta 13C in wood responded to rainfall events, but carbohydrate storage and reallocation also affected the isotopic signature. Although delta 13C in wood of any one species varied over a range of 2 to 4 per thousand, there was a general relationship between delta 13C of the leaves and the annual range of delta 13C in wood. We conclude that species-specific traits are important in understanding the response of Eucalyptus to rainfall and that the diversity of the genus may reflect its response to the large climatic gradient in Australia and to the large annual and interannual variations in rainfall at any one location.  相似文献   

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