On the distribution of tree growth stresses ? Part I: An anisotropic plane strain theory

Tree growth stress, resulted from the combined effects of dead weight increase and cell wall maturation in the growing trees, fulfills biomechanical functions by enhancing the strength of growing stems and by controlling their growth orientation. Its value after new wood formation, named maturation stress, can be determined by measuring the instantaneously released strain at stem periphery. Exceptional levels of longitudinal stress are reached in reaction wood, in the form of compression in gymnosperms or higher-than-usual tension in angiosperms, inspiring theories to explain the generation process of the maturation stress at the level of wood fiber: the synergistic action of compressive stress generated in the amorphous ligninhemicellulose matrix and tensile stress due to the shortening of the crystalline cellulosic framework is a possible driving force. Besides the elastic component, growth stress bears viscoelastic components that are locked in the matured cell wall. Delayed recovery of locked-in components is triggered by increasing temperature under high moisture content: the rheological analysis of this hygrothermal recovery offers the possibility to gain information on the mechanical conditions during wood formation. After tree felling, the presence of residual stress often causes processing defects during logging and lumbering, thus reducing the final yield of harvested resources. In the near future, we expect to develop plantation forests and utilize more wood as industrial resources; in that case, we need to respond to their large growth stress. Thermal treatment is one of the possible countermeasures: green wood heating involves the hygrothermal recovery of viscoelastic locked-in growth strains and tends to counteract the effect of subsequent drying. Methods such as smoke drying of logs are proposed to increase the processing yield at a reasonable cost.

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“…This process could be rationally simulated on the basis of the elastic theory for a polar-anisotropic cylinder [6][7][8][9][10][11][12]. Fig.…”

Section: Biomechanical Functions Of Growth Stress Typical Growth Strementioning

confidence: 99%

Tree growth stress and related problems

et al. 2017

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“…As a result, cells tend to modify their dimensions and generate stresses in wood. Several authors have proposed models describing the distribution of maturation stresses within the stem [5,6,26,28,47]. Using these models, Thibaut et al [63] gave a qualitative illustration of how longitudinal, tangential and radial stresses are distributed in the stem ( figure 2).…”

Section: Growth Stressesmentioning

confidence: 99%

Ring shake in chestnut (Castanea sativa Mill.): State of the art

Fonti

Macchioni²,

Thibaut

2002

Ann. For. Sci.

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-Too often chestnut wood (Castanea sativa Mill.) becomes economically uninteresting because of the high risk of ring shake to which this species is prone. For more than twenty years chestnut ring shake has been the subject of studies undertaken in an effort to understand its underlying causes and mechanisms. Since not all aspects of the phenomenon have been sufficiently studied at the present time, ring shake has not yet been completely elucidated. However, it is possible to outline a general framework of the phenomenon and advance preliminary ideas on the causes that contribute to the development of this type of fracture. This article summarises the current state of knowledge, discusses the possible causes and proposes measures to reduce the risk of ring shake occurrence in chestnut.ring shake / Castanea sativa Mill. / wood / residual stresses / mechanical strength Résumé -La roulure du châtaignier (Castanea sativa Mill.): connaissances actuelles. Trop souvent le bois de châtaignier (Castanea sativa Mill.) perd son intérêt économique à cause du haut risque de roulure qui affecte cette espèce. Depuis plus de vingt ans la roulure du châtaignier fait l'objet de plusieurs études vouées à la compréhension des causes et des mécanismes qui conduisent à sa formation. À l'état actuel tous les aspects n'ont pas été suffisamment étudiés pour que l'on puisse considérer la roulure comme un phénomène complè-tement élucidé. Malgré cela, un cadre général du phénomène peut être esquissé et des premières réflexions sur les causes qui mènent à l'apparition de ce type de fracture peuvent être avancées. Cet article résume l'état des connaissances acquises à ce jour, discute les causes possibles et propose des mesures afin de diminuer le risque d'apparition de la roulure chez le châtaignier. roulure / Castanea sativa Mill. / bois / contraintes résiduelles / résistance mécanique Ann. For. Sci. 59 (2002) 129-140 129

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“…Though the changes were related to changes in water and solute¯ows, it is not unlikely that they also contained a component due to a redistribution of TS states due to cutting. An analogy would be the redistribution of TGSs during crosscutting of logs (see Archer 1987).…”

Section: Tissue Stressesmentioning

confidence: 99%

Graviresponses in herbs and trees: a major role for the redistribution of tissue and growth stresses

Hejnowicz¹

1997

Planta

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Tissue stresses, which occur in turgid herbaceous stems, both elongating and non-elongating. and tree growth stresses (TGSs) which occur in woody stems, are similar in that (i) they form self-equilibrating patterns of stresses (tensile and compressive) in stems, and (ii) the asymmetric, graviresponsive change in the pattern tends to bend the stem. The longitudinal tensile tissue stress (TS) which occurs in the outer layers of turgid stems is a few times higher than the osmotic pressure of cell sap in such a layer. Usually it is considered that TSs originate from the differential growth of tissues in a stem; however, physical analysis of a turgid stem model has shown that TSs are an unavoidable physical consequence of the variation in structural characteristics of cell layers or vascular strands in turgid stems. The model applied to the sunflower hypocotyl gives forces which fit well to those measured. The structural characteristics are sufficient to explain fully the TSs which exist in turgid stems. Differential growth is not necessary in this respect. Examination of the model shows also that the longitudinal elastic strain of all cell walls in a turgid stem is the same at a given stem level regardless of wall thickness, i.e. the structure-based TSs compensate for the variation in turgor-induced wall stress in single cells with variable diameter and wall thickness. The importance of this compensation for the anisotropy of wall stresses is presented. The forces which generate TSs exert bending moments which are high but they sum mutually to zero in a vertical stem. In gravistimulated turgid stems of Reynoutria, the TSs decrease considerably on the lower side while those on the upper side remain unaltered. The consequences of this asymmetric change for gravitropic bending are analysed. Tree growth stresses arise in a process by which new cells added by the cambium to the secondary xylem tend to shrink longitudinally (except compression wood) during maturation of the cell walls. The pattern of TGSs is characterized by tensile or compressive stress in the peripheral or the core wood, respectively. An asymmetrical pattern of TGSs due to asymmetrical deposition of wood results in a bending moment which equilibrates the bending moment caused by the weight of a lateral branch. In response to a gravity-derived stimulus the TGS pattern may be modified by asymmetric formation of reaction wood which differs histologically from normal wood: tension wood in many arborescent angiosperms, and compression wood in conifers. The formation and functioning of the reaction wood is discussed.

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On the distribution of tree growth stresses ? Part I: An anisotropic plane strain theory

Cited by 39 publications

References 6 publications

Tree growth stress and related problems

Tree growth stress and related problems

Ring shake in chestnut (Castanea sativa Mill.): State of the art

Graviresponses in herbs and trees: a major role for the redistribution of tissue and growth stresses

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