Wood, elastic properties

Astbury, W. T. Street, A., X-ray Studies of the Structure of Hair, Wool and Related Fibres. I. General. Trans. R. Soc. London 1931, A230,75 Astbury, W. T. Woods, H. J., II. The Molecular Structure and Elastic Properties of Hair Keratin. ibid. 1934, A232, 333 Astbury, W. T. Sisson, W. A., III. The Configuration of the Keratin Molecule and its Orientation in the Biological Cell, Proc. R. Soc. London 1935, A150, 533. 

Astbury WT, Woods HJ (1933) X-ray studies of the structure of hair, wool, and related fibres, II. Molecular structure and elastic properties of hair keratin. Items R Soc A232 333-394... 

The extensive investigations by Astbury and Woods (1933) of the X-ray diffraction patterns of animal fibers before and after stretcihing, setting, or supercontraction (Section VI,5,2) have had a major influence on the models proposed to account for the load-extension properties. Astbury and Woods showed that when animal fibers are stretched, the characteristic a-pattern decreases in intensity with the simultaneous appearance of a d-pattern similar to that obtained from silk. The sharpness and intensity of the /3-pattern increases with sti ain, with temperature, and with time under strain. In the Hookean region the 5.1 A meridional spacing increases by up to 2 % (Astbury and Haggith, 1953). Astbury and Woods (1933) stated that virtually no /3-pattern appears until the fiber has been stret( hed by at least 20 %, and for 25 years this observation dominated the models proposed to explain the elastic properties of wool (Alexander and Hudson, 1954). 

Astbury, W. T., and Woods, H. J. The X-ray interpretation of the structure and elastic properties of hair keratin. Nature (London) 126, 913-914 (1930). Astbury, W. T., and Street, A. X-ray studies of the structure of hair, wool and related fibers. Phil. Trans. Roy. Soc. (London) A230, 75-101 (1931). 

Harada H and Cote WA (1985) Structure of wood. In Higuchi T (ed). Biosynthesis and biodegradation of wood components. Academic Press, London, 1-42 Harrington 11 (2002) Hierarchical modelling of softwood hygro-elastic properties. Ph.D thesis. University of Canterbury, Christchurch, New Zealand Harris IF (1976) Acid hydrolysis and dehydration reactions for utilizing plant carbohydrates. In Timell TE (ed). Proceedings of 8th cellulose conference. Wiley, New York, Vol. 1 131-44... 

Magnesium oxychloride cement (see section 15.1) is also well suited to be combined with wood. Such a combination is most commonly used for industrial floorings. The main advantage of this material in such applications is its favorable elastic properties. 

In an innovative study, nanoscale characterization of natural fibres using contact-resonance force microscopy (CR-EM) was reported by Sandeep et al. [44]. This method was used to evaluate the cell wall layers of natural fibres for studying the elastic properties of cell walls. The cell wall layer experiments involved samples collected from a 45-year-old red oak. The studies revealed that there is a thin region between the SI and S2 layers with apparently lower modulus than that of other secondary layers. Eigure 1.12 shows schematic representation of cell wall layers of wood fibre. Eigure 1.13 shows images for the topography and indentation modulus. Contrasts in modulus between the compound middle lamellae (CML) and SI and S2 layers are clearly visible. Mean values of the indentation... 

D.V. Doyle, J.T. Drow, and R.S. McBurnery, Elastic Properties of Wood - the Young s Modulus and Poisson s Ratio of Balsa and Quipo, Report No. 1528, U.S. Department of Agriculture, Forest Products Laboratory, Madison, Wisconsin (1945). 

Lee C, Wei X, Kysar JW, Hone J (2008) Measurement of the elastic properties and intrinsic strength of monolayer graphene. Science 321(5887) 385-388 Lee SH, Doherty TV, Linhardt RJ, Dordick JS (2009) Ionic liquid-mediated selective extraction of lignin from wood leading to enhanced enzymatic cellulose hydrolysis. Biotechnol Bioeng 102 (5) 1368-1376... 

The tensile test is the experimental stress-strain test method most widely employed to characterize the mechanical properties of materials like plastics, metals, and wood. From any complete test record one can obtain important information concerning a material s elastic properties, the character and extent of its plastic deformation, and its yield and tensile strengths and toughness. That so much information can be obtained from one test of a material justifies its extensive use. To provide a framework for the varied responses to tensile loading in load-bearing materials that occur, several stress-strain plots, reflecting different deformation characteristics, will be examined. 

The mechanical properties of wood tend to increase when it is cooled and to decrease when it is heated (6,18). If untreated wood heated in air is not exposed to temperatures of more than - 70° C for more than about 1 year, the decrease in properties with increasing temperature is referred to as immediate or reversible ie, the property would be lower if tested at the higher temperature but would be unchanged if heated and then tested at room temperature. The immediate effect of temperature on strength and modulus of elasticity of clear wood, based on several different loading modes, is illustrated in Figures 4—6 (6). 

Higher temperatures result in permanent degradation. The amount of this irreversible loss in mechanical properties depends upon moisture content, heating medium, temperature, exposure period, and, to some extent, species. The effects of these factors on modulus of mpture, modulus of elasticity, and work to maximum load are illustrated in Figures 6—9 (6). The effects may be less severe for commercial lumber than for clear wood heated in air (Fig. 10). The permanent property losses shown are based on tests conducted after specimens were cooled to - 24° C and conditioned to a moisture content of... 

Lord Kelvin s close associate, the expert experimentalist J. P. Joule, set about to test the former s theoretical relationship and in 1859 published an extensive paper on the thermoelastic properties of various solids—metals, woods of different kinds, and, most prominent of all, natural rubber. In the half century between Gough and Joule not only was a suitable theoretical formula made available through establishment of the second law of thermodynamics, but as a result of the discovery of vulcanization (Goodyear, 1839) Joule had at his disposal a more perfectly elastic substance, vulcanized rubber, and most of his experiments were carried out on samples which had been vulcanized. He confirmed Gough s first two observations but contested the third. On stretching vulcanized rubber to twice its initial length. Joule ob-... 

When we compared the viscosities of solutions of natural rubber and of guttapercha and of other elastomers and later of polyethylene vs.(poly)cis-butadiene, with such bulk properties as moduli, densities, X-ray structures, and adhesiveness, we were greatly helped in understanding these behavioral differences by the studies of Wood (6) on the temperature and stress dependent, melting and freezing,hysteresis of natural rubber, and by the work of Treloar (7) and of Flory (8) on the elasticity and crystallinity of elastomers on stretching. Molecular symmetry and stiffness among closely similar chemical structures, as they affect the enthalpy, the entropy, and phase transitions (perhaps best expressed by AHm and by Clapeyron s... 

The mathematical relationship between the stress and the strain depends on material properties, temperature, and the rate of deformation. Many materials such as metals, ceramics, crystalline polymers, and wood behave elastically at small stresses. For tensile elastic deformation, the linear relation between the stress, a, and strain, e, is described by Hooke s law as... 

Gerhards (57) reviewed the results of 12 separate studies on strength properties of fire-retardant-treated wood conducted at the FPL and other laboratories. He concluded that modulus of rupture (MOR) is consistently lower and modulus of elasticity (MOE) and work to maximum load are generally lower for fire-retardant-treated wood than for untreated wood if fire-retardant treatment is followed by kiln drying. The effect may be less or negligible if the fire-retardant-treated wood is air dried instead of kiln dried. The most significant loss was in work to maximum load, a measure of shock resistance or brashness, which averaged 34 percent reduction. 

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