Resin Pocket Formation in Tree Stems of Dahurian Larch

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UDС

674.038.1

DOI:

10.17238/issn0536-1036.2017.5.35

Abstract

The paper analyzes the study results of native and foreign authors of the strain-stress state and distribution of internal stresses in a tree stem. The cyclic tensile and compressive stresses, arising at the wind load, are superimposed on the initial stresses when their further modifications in the tree growth process. The tree stem as a balanced system and a living organism strives to compensate the arising loads by increasing the density of cell walls and changing their structure – twisting. The occurrence of extreme loads and cyclic rocking loads can cause microdamages – cracks. The cavities of coniferous trees are filled with a natural antiseptic - resin. A further increase of cavities and filling of resin pockets occur under the influence of fluctuating compression and tensile stresses. In accordance with the nature of initial stresses in the radial and tangential directions, the pockets on the average are longer in the zones of the greatest radial tensile stresses. The goal of research is the substantiation of the location of the greatest resin pockets accumulation. Based on the fact that the shape of a trunk corresponds to the shape of a rod of equal resistance, in which the stresses in the outer fibers during bending should be the same over the entire height of the tree, we have calculated the circumferential and radial stresses along the radius of the stem cross section. Taking into account the relationship between the size of the core zone, stresses at the center and along the outline of the section and ultimate strength of wood under static bending and compression, the authors have used the distribution function of the initial longitudinal stress in the form of a paraboloid of the 14th degree to calculate the initial stresses in the Dahurian larch stem by the material resistance methods. As a result, the epure of stem total stress has been obtained. According to the generalized Hooke's law, we have designed a distribution graph of the main relative strain in the radial direction along the diameter of the stem cross section. As a confirmation of the theory of the resin pockets formation, we have conducted the laboratory tests to determine the strength limits when static bending and compression along the fibers, taking into account the ratio of radii of heartwood and sapwood in the samples. The study of the pocket localization along the diameter of the stem cross section of Dahurian larch has proved that the greatest resin pockets accumulation is in the zone of maximum radial deformation.

Authors

V.N. Glukhikh 1, Doctor of Engineering Sciences, Professor
A.Yu. Okhlopkova 2, Wood Process Engineer

Affiliation

1Saint Petersburg State University of Architecture and Civil Engineering,
Vtoraya Krasnoarmeyskaya ul., 4, Saint Petersburg, 190005, Russian Federation; e-mail: vnglukhikh@mail.ru
2Woodworking Complex “Asia Les”, per. Oblachnyi, 78A, off. 11, Khabarovsk, 680030, Russian Federation; e-mail: anna.okhlopkova@gmail.com

Keywords

wood, tree stem, strain-stress state, internal and initial stress, growth stress, resin pocket, Dahurian larch

For citation

Glukhikh V.N., Okhlopkova A.Yu. Resin Pocket Formation in Tree Stems of Dahurian Larch. Lesnoy zhurnal [Forestry journal], 2017, no. 5, pp. 35–52. DOI: 10.17238/issn0536-1036.2017.5.35

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Received on March 15, 2017