ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1975.tb04001.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SUMMARYFollowing a brief introduction concerned with present consumption and future prospects of timber and timber products the principal structure‐property relationships of this low density, cellular, polymeric composite are reviewed and discussed. Structure is examined at four levels of magnitude—macroscopic, microscopic, sub‐microscopic and chemical—and the various models used to interpret its composite nature are described.The dimensional instability of timber and loss of strength on wetting are discussed in terms of its fine structure. At low levels of stressing, and for short periods of time, timber can be treated as an elastic material, but at higher stresses and prolonged periods, especially with alternating humidity, timber behaves as a linear orthotropic viscoelastic material; the various factors influencing the elastic constants and the relationship of creep to fine structure are discussed.The anisotropy of wood is related to cell arrangement and microfibrillar orientation: strength and its variability are discussed in terms of structure at all four levels. Comparison of the strength of timber with that of other constructional materials especially on a weight basis shows timber in a very good light; the combination of high stiffness and high toughness is unique. Recent models using three‐dimensional anisotropic elastic analysis to understand strength and deformation of timber are described. The morphology of fracture under different forms of stressing is il

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1975.tb04002.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SUMMARYStudy of the gaseous permeability of wood stored in ponds to promote bacterial decomposition of the bordered pit membranes has shown that the pit aperture/pit cavity contributes to the total resistance to flow of liquids through both ponded and unponded wood. In ponded wood the contributions of the pit apertures/pit cavities ranged between 5% and 46% of the total resistance, the tracheid lumina making up the remaining 96–54%. This large variation is attributed to the presence of different proportions of earlywood and latewood in specimens tested. In air‐dried unponded wood, however, the pit membrane pores contribute an average of 81% of the total resistance to liquid flow, the tracheid lumina an average of 16%, and the pit aperture an average of only 3%. An implication of these results is that previously used analytical techniques for the determination of the radius and number of conducting flow paths in wood, based on the assumption that only two structural components offer resistance to flow, are not wholly satisfact

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1975.tb04003.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SUMMARYA constitutive relation for an elastic fibre composite material consisting of an inert fibrous phase embedded in a water‐reactive matrix has been derived. The relation is determined in terms of the overall stiffness of the composite, the volume proportion of the matrix, and stiffness and sorption functions of the matrix that are dependent on moisture content. The proposed model of the matrix is believed to be appropriate to wood substance. The constitutive relation is, therefore, applicable to a basic element of wood substance and can be applied to models of wood structure to calculate mechanical properties such as shrinkage, moisture‐induced creep and other moisture‐related prope

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1975.tb04004.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SUMMARYResearch activity in wood anatomy since 1900 is reviewed with special reference to the pattern of development in (1) descriptive and comparative anatomy, (2) structure in relation to wood properties and (3) the influence of growth on wood structure. In the early decades of the century there was an emphasis on comparative anatomy, often as a contribution to developing the use of the tropical forest resource. At the same time, there was an increasing awareness that an understanding of the behaviour of wood was to be obtained from the study of its physical structure and chemical composition; particular attention has been given to elucidating the structure of the cell wall, at first by conventional optical microscopy and physical techniques and more recently by electron‐ and scanning electron‐microscopy. Studies of the interaction between growth and wood structure have attracted special interest in the post Second World War period and have been prompted by an awareness in many countries for a need to depend increasingly on managed forests as a source of timber and to produce such timbers at minimum cost compatible with acceptable technical performance.Finally, in considering the future of wood anatomy, the view is expressed that if a continuing and more effective use is to be made of wood, then wood anatomy must have a future as it has a fundamental role in developing and applying the technology of wood. Particularly important is its role in contributing to the use of the world's timber resource, especially the many under‐utilized timbers in the developing countries, and the efficient production of plantation t

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1975.tb04005.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SUMMARYThe wood anatomy ofAlzateafrom South America,Axinandra, CrypteroniaandDactylocladusfrom South East Asia, andRhynchocalyxfrom South Africa is described in detail. Special attention has been given to the ultrastructure of vestured pits in the five genera. The grouping of these genera into one family as suggested recently is not supported by wood anatomy.AlzateaandRhynchocalyxdiffer widely from the three other genera and appear to share many characters with both Lythraceae and Melastomataceae; the latter family shows a wide wood anatomical range. The wood anatomical affinities ofAxinandra, CrypteroniaandDactylocladusare with Melastomataceae. Comparisons with some other Myrtalean families, notably Oliniaceae and Sonneratiaceae, indicate intimate relationships between Melastomataceae, Lythraceae, Oliniaceae, Sonneratiaceae and Crypteroniaceae s.l. because of overlapping of the wood anatomical range among these families.

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1975.tb04006.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SUMMARYA method is described to measure the content of methylmethacrylate‐polymer (poly‐MMA) in wood‐plastic composites and the influence of MMA on water and ethanol accessibility of beech wood fibre walls using interference microscopy. Although theS2‐layer of the fibre wall is capable of containing about 12% volume of plastic, the effect of treatment on ultimate water absorption of the cell wall is negligible. The ultimate absorption of ethanol is, however, completely reduced to zero. Increased dimensional stability of wood‐poly‐MMA composites is probably due to hindrance by the plastic in the lumina of the wood elements. The interference microscopic method is also shown to be suitable for determination of the fibre saturation point of cell

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1975.tb04007.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

SUMMARYThe importance of density as an indicator of wood quality, and the need to measure density rapidly, accurately and on a large scale, have led to the development of the techniques described in this paper.The principles of X‐ray radiography on which the method is based are described briefly. Problems that have arisen in the development of the techniques are discussed, together with the solutions proposed for them. The routine procedure now used at the Department of Forestry, Oxford, for X‐ray radiography of wood specimens, and for examination of radiographs by optical densitometry, is explained. A system for the sorting and presentation of data for the application is given in outline, together with a note on the statistical techniques that have been found useful for analysis of data and interpretation of results.Of the structural features and physical and chemical properties that determine the behaviour of wood in manufacturing processes and its characteristics in use, density is the most important.Density is closely related to physical properties, such as hardness and mechanical strength, it gives a good estimation of the yields likely to be obtained in pulping, and it may be a useful indicator of behaviour in drying and resistance to cutting and machining.The wood technologist and the wood user have to take account of the influence of density in several ways. There is a very great range of variation between different species of trees in their mean values for density. This is a primary consideration in the selection of species for a particular purpose, and in general is an advantageous situation, in that tree species can be found for a wide range of applications.When a species has been selected as suitable for a particular purpose, there may still be problems concerning density, if there is considerable variation in density within trees, particularly from the pith outwards, or if there is considerable variation between trees in mean values for density.To make this point more precisely, it has been demonstrated, with some species, that differences in density for mean values of trees from the same site are greater than the differences for mean site values, over a very wide range of geographical distribution and of climatic and soil types. The variation in density within the stem of individual trees, although this is not generally recognized, may be an even more serious matter for concern with some species, particularly in fast grown plantation crops, where the wood near the pith may be less than half of the density of the wood near the bark.Because of the occurrence of considerable variability in wood density, some species are regarded as unsuitable for purposes where the specifications are exacting, for example for some constructional purposes. With many species, however, it should be possible to minimize the adverse effects of within‐tree and between‐tree variability, by appropriate silvicultural treatment of the crops and by selection of trees that have an inherently more uniform pattern of development of density.It is this possibility that has provided the incentive to find and to improve the methods for the measurement of wood density that are described in this paper. If silvicultural treatments for the improvement of wood quality are to be applied on a worthwhile scale, then methods are required by which large numbers of specimens can be accurately and rapidly measured, and that also facilitate the estimation and comparison both of whole tree values for density and within‐tree patterns of the development o

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1975.tb04008.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY

摘要:

Book reviewed in this article:Microprobe Analysis as Applied to Cells and Tissues. Ed. by T. Hall, P. Echlinand R. Kaufmann.Quantitative Scanning Electron Microscopy. Ed. by D. B. Holt, M. D. Muir, P. R. Grantand I. M. Boswarva.

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1975.tb04009.x

出版商:Blackwell Publishing Ltd    

年代:1975

数据来源: WILEY