Growth stress patterns in tree stems
Tóm tắt
Growth stresses originate in maturation strains, induced in cambial layers during the differentiation and the maturation of new cells, impeded by the mass of the whole trunk. To predict stresses in a stem, one must add successive incremental stresses at successively created points of the growing trunk. Usual measurements of released strains at the surface of a stem do not give the evolution of maturation strains with growth. As the assumption that states that maturation strains are constant since the beginning of secondary growth leads to singularities near the pith, an empiric pattern of variation of maturation strains along the radius is proposed, using observations about relationships between released longitudinal strain and microfibril angle. Furthermore, assuming an elastic, orthotropic behavior law and a cylindrical, sufficiently long stem, residual stresses are computed and discussed. For hardwoods, far enough from the pith, patterns of computed longitudinal and tangential stresses agree with distributions already stated by other authors although these stress components are limited near the pith. Computed radial stresses have lower levels than commonly admitted. On the other hand, stress-distributions in young softwoods are found very different, especially near the pith where the longitudinal component appears tensile and the tangential one compressive.
Tài liệu tham khảo
Archer, R. R.; Byrnes, R. E. 1974: On the distribution of tree growth stresses. Part I: An anisotropic plane strain theory. Wood Sci. Technol. 19: 259–276
Archer, R. R. 1986a: Growth stresses and strains in trees. In: T. E. Timell (Ed.): Springer Series in Wood Science. Berlin: Springer Verlag
Archer, R. R. 1986 b: Application of a new method for growth stress measurement to Pinus caribaea. Proc. IUFRO Proj. Group P.5.01. Properties and utilization of tropical wood, Manaus, Brazil Nov. 19–23, 1984
Archer, R. R. 1987: On the origin of growth stresses in trees. Part 1: Micromechanics of the developing cambial cell wall. Wood Sci. Technol. 21: 139–154
Bamber, R. K. 1987: The origin of growth stresses: a rebuttal. IAWA Bull. n.s. Vol. 8(1)
Beck, J. L. 1974: Anisotropic theory of growth stresses in trees. Phys. Eng. Lab. Dep. Sci. Ind. Res. Lower Hutt, Zew Zealand, Rep. 452
Bordonne, P. A.; Okuyama, T.; Yamamoto, H.; Iguchi, M. 1987: Relationships between growth stresses and microfibril angle in cell walls. Réunion IAWA-IUFRO, De la formation de la paroi cellulaire au comportement du bois, Paris, France Dec. 9–11, 1987
Boyd, J. D. 1950: Tree growth stresses evaluation. Aust. J. Sci. Res. B3: 270–293
Boyd, J. D. 1972: Tree growth stresses — Part V: Evidence of an origin in differentiation and lignification. Wood Sci. Technol. 6: 251–262
Chardin, A. 1984: Les contraintes de croissance du Wapa. Étude en vue de déterminer les ≪conditions technologiques d'utilisation du Wapa, principale essence de Guyane≫. Compte rendu de fin d'études 79 2 34 0535, Centre Technique Forestier Tropical, Nogent-sur-Marne
Ferrand, J. C. 1981: Recherche des solutions pratiques à apporter aux problèmes posés par les constraintes de croissance des arbres forestiers. Thesis D.I. Bois I.N.P. de Lorraine
Gillis, P. P.; Hsu, C. H. 1979: An elastic, plastic theory of longitudinal growth stresses. Wood Sci. Technol. 13: 93–115
Gueneau, P. 1973: Contraintes de croissance. Cahiers Scientifiques no. 3 de Bois et Forêts des Tropiques. C.T.F.T. Nogent sur Marne
Guitard, D. 1987: Mécanique du matériau bois et composites. Collection Nabla, Cepadues Editions Toulouse, France
Kubler, H. 1959a: Studien über Wachstumsspannungen des Holzes. Erste Mitteilung: Die Ursache der Wachstumsspannungen und die Spannungen quer zur Faserrichtung. Holz Roh-Werkstoff 17: 1–9
Kubler, H. 1959b: Studien über Wachstumsspannungen des Holzes. Zweite Mitteilung: Die Spannungen in Faserrichtung. Holz Roh-Werkstoff 17: 44–54
Kubler, H. 1987: Growth stresses in trees and related wood properties. Forestry Abstr. Vol. 48, No. 3
Maiti, M.; Adams, S. F. 1968: Isotropy at the center of a cylindrical wood pole. Wood Sci. Technol. 2: 44–45
Okuyama, T.; Kikata, Y. 1975: The residual stress distributions in wood log measured by “Thin layer removal method”. J. Soc. Mat. Sci. Japan 24(264) 845–848
Okuyama, T.; Sasaki, Y. 1978: The residual stresses in wood logs due to growth stresses. (IV). Mokuzai Gakkaishi 24: 77–84
Preziosa, C.; Guitard, D.; Sales, C. 1986: Internal stresses in wood shrinkage: the stress shrinkage tensor as an isotropic characteristic of wood materials. Cahiers Scientifiques No. 8, Bois et Forêts des Tropiques. C.T.F.T. Nogent sur Marne
Sasaki, Y.; Okuyama, T.; Kikata, Y. 1978: The evolution process of the growth stress in the tree. Mokuzai Gakkaishi 24: 149–157
Tahani, N. 1988: Modélisation des contraintes internes dans les matériaux orthotropes cylindriques: séchage d'un billon soumis à un gradient radial d'humidité. Thesis Doctorat I.N.P. de Lorraine
Watanabe, H. 1965: A study of the origin of longitudinal growth stresses in tree stems. Vol. 1. IUFRO Sec. 41 Meet. Melbourne
Yamamoto, H.; Okuyama, T. 1988: Analysis of the generation process of growth stresses in cell walls. Mokuzai Gakkaishi 34: 788–793