A numerical study of the shape stability of sawn timber subjected to moisture variation Part 1: Theory

Ormarsson, Sigurdur; Dahlblom, Ola; Petersson, Hans

doi:10.1007/bf00702789

Cited by 49 publications

(20 citation statements)

References 6 publications

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“…It should be observed whether the discs are cracked and how is the crack development in the course of the drying process. The experimental disc samples will also be simulated by a 3D distortion model developed by Ormarsson et al (1998Ormarsson et al ( , 1999. The crack simulation by finite element modeling (FEM) in the present study is based on description of a cohesive crack model for wood.…”

Section: Introductionmentioning

confidence: 99%

Experimental and finite element study of the effect of temperature and moisture on the tangential tensile strength and fracture behavior in timber logs

Larsen

Ormarsson

2013

Holzforschung

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Timber is normally dried by kiln drying, in the course of which moisture-induced stresses and fractures can occur. Cracks occur primarily in the radial direction due to tangential tensile strength (TSt) that exceeds the strength of the material. The present article reports on experiments and numerical simulations by finite element modeling (FEM) concerning the TSt and fracture behavior of Norway spruce under various climatic conditions. Thin log disc specimens were studied to simplify the description of the moisture flow in the samples. The specimens designed for TS were acclimatized to a moisture content (MC) of 18% before TSt tests at 20°C, 60°C, and 90°C were carried out. The maximum stress results of the disc simulations by FEM were compared with the experimental strength results at the same temperature levels. There is a rather good agreement between the results of modeling and experiments. The results also illustrate the strong decrease of TSt with increasing temperature at a constant MC level.

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Section: Introductionmentioning

confidence: 99%

Experimental and finite element study of the effect of temperature and moisture on the tangential tensile strength and fracture behavior in timber logs

Larsen

Ormarsson

2013

Holzforschung

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“…It observed that after the cut, the wood is often exposed in open air and submitted to environmental and climate loading during a long time [13]. With the drying cycle actions, the micro cracks are initiated and can propagate under the creep loading when the wood is used as timber structures.…”

Section: Introductionmentioning

confidence: 99%

Stress Intensity Factors for Viscoelastic Axisymmetric Problems Applied to Wood

Pitti

Chazal

Labesse-Jied

et al. 2012

Conference Proceedings of the Society for Experimental Mechanics Series

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ABSTRACT. Many materials used in engineering applications obey to time-dependent behaviours and the mechanical fields are affected by the time effects. As a result, the evolution of the stresses and strains in these materials appear still very complex and difficult to study. Among such cases is the situation when the material has an axisymmetric shape and when it is submitted to a complex fracture loading. In this paper, the creep loading is applied on an axisymmetric viscoelastic orthotropic material and the stress intensity factors are computed in the opening mode, in the shear mode and in the mixed mode using to a finite element approach. The uncoupling method is based on M integral, combining the virtual and real mechanical fields. In the same time, the viscoelastic effects are introduced according to the generalized Kelvin-Voigt model composed by four branches. The numerical solution is obtained with an incremental viscoelastic formulation in the time domain. Using a Compact Tension Shear (CTS) specimen, the evolutions of stress intensity factor versus time are posted in each fracture mode configuration. The obtained results demonstrate the efficiency of the proposed model.

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“…The significance of these parameters was studied using some analytical models (Stevens and Johnston 1960;Booker 2005;Bäckström and Johansson 2006), as well as statistics from data on stationary conditioning experiments Warensjo and Rune 2004) and numerical modelling (Ormarsson et al 1998). In most cases ring curvature was found to be the best predicting variable, or had the greatest impact on twist variation, followed by GA.…”

Section: Introductionmentioning

confidence: 99%

The influence of material properties on the amount of twist of spruce wood during kiln drying

et al. 2010

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The development of twist in Norway spruce boards (Picea abies Karst.) during normal temperature kiln drying was researched. Tangentially oriented boards were sawn from diametrical radial planks, from which the basic wood properties, i.e. linear shrinkage and grain angle, were determined. The unrestrained boards were kiln dried using a selected drying schedule. During the controlled drying process the moisture content (MC) and twist of the boards were measured. Twist was generally induced by the shrinkage of wood below the fibre saturation point, and increased in proportional to the decrease in MC. The earlier appearance of twist, with regard to MC and drying time, was confirmed in the case of boards sawn from the central part of logs. The final twist amounted to between 10 and 20 °/m in the case of boards close to the pith, and decreased to less than 4 °/m in the case of boards sawn at a radius of 70 mm from the centre of the logs. Ring curvature had the highest impact on the final twist of the dried boards, followed by grain angle and tangential shrinkage. Einfluss der

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A numerical study of the shape stability of sawn timber subjected to moisture variation Part 1: Theory

Cited by 49 publications

References 6 publications

Experimental and finite element study of the effect of temperature and moisture on the tangential tensile strength and fracture behavior in timber logs

Experimental and finite element study of the effect of temperature and moisture on the tangential tensile strength and fracture behavior in timber logs

Stress Intensity Factors for Viscoelastic Axisymmetric Problems Applied to Wood

The influence of material properties on the amount of twist of spruce wood during kiln drying

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