Wood as a linear orthotropic viscoelastic material

Schniewind, Arno P.; Barrett, J. D.

doi:10.1007/bf00351807

Cited by 95 publications

(55 citation statements)

References 9 publications

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“…At low strain and stress levels, its behavior is also nonlinear viscoelastic but less prominent that allows for the assumption of linear viscoelasticity to be a good approximation (Morlier and Palka 1994). This was confirmed with the experimental results presented in this paper as well as in numerous other experimental studies (e.g., Echeniques-Manrique 1969; Schniewind and Barrett 1972;Hanhijärvi 1999;Hunt 1999). The assumption of linear viscoelasticity at low strain or stress levels of wood is especially convenient when predicting material behavior by means of linear 'spring-dashpot' models.…”

Section: Modelingsupporting

confidence: 90%

“…A recent review on the topic has been made by Navi and Stanzl-Tschegg (2009). Evidently, many studies consider creep behavior of wood (e.g., Ożyhar et al 2013;Schniewind and Barrett 1972;Taniguchi and Ando 2010;Kawahara et al 2015), while the experimental research on stress relaxation is very limited. This is somehow puzzling, since it has been established that wood experiences rheological behavior whether the deformation or the stress is held constant; meaning that the rheological behavior of wood is characterized by both creep of strain and stress relaxation phenomena.…”

Section: Introductionmentioning

confidence: 99%

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Rheological behavior of wood in stress relaxation under compression

2018

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Rheological behavior of wood under uniaxial compression along and perpendicular to the grain in constant environment was examined. Tests with constant deformation rate until failure and stress relaxation tests with constant deformation applied stepwise were carried out. The experimental results of stress relaxation showed nonlinear material behavior over time that got more prominent under high deformation levels. Considerable amount of stress relaxed during applying the deformation. Wood experienced greater stress relaxation along the grain than perpendicular to it. Three rheological models for orthotropic material were calibrated to the experimentally determined stress-time curves in longitudinal and transverse directions simultaneously. Small deformation levels assuming linear strains were accounted for in the models. Required elastic material parameters were determined from the tests with constant deformation rate. A model including the highest number of viscoelastic material parameters was the most successful in predicting stress relaxation of wood under stepwise deformation. Modeling indicated that wood behavior was very close to linear viscoelastic in relaxation under small deformation. The obtained material parameters made the model suitable for predicting rheological behavior of wood comprehensively, under sustained deformation or load in constant conditions.

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Section: Modelingsupporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Rheological behavior of wood in stress relaxation under compression

2018

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“…lower the moisture content asymmetry over time, decreasing the deflection. Also expansion is presumed to follow the change in moisture content immediately, whereas in literature viscoelastic effects are assigned to wood [37]. These time-dependent effects can attenuate the bending of the board.…”

Section: Step Responsementioning

confidence: 99%

Hygromorphic response dynamics of oak: towards accelerated material characterization

2017

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When a wood board is exposed to a change in relative humidity on only one of its surfaces, e.g. in case of flooring or a panel painting, the resulting asymmetric moisture content profile induces differential expansion over the thickness. Consequently a bending moment causes the board to curve. A theory is presented to describe the bending of a wood board due to a step change in relative humidity. The board is assumed to be homogeneous, isotropic, and linearly elastic. Moisture transport is presumed to obey the diffusion equation with constant coefficients, such that moisture transport can be directly related to the bending of the board. It is shown that the transient deflective behavior provides the diffusion coefficient and the final length change yields the linear hygroscopic expansion coefficient. Derived diffusion coefficients are in good agreement with values in literature. Furthermore, a scaling law for the deflection of the board is proposed, which is seen to be followed qualitatively but not quantitatively by experiments. Finally, by assuming the deflection of the board to be the response of a linear system, the deflective frequency response of the board can be predicted from its step response. The results allow upscaling of deflection and expansion, such that behavior of thick boards can be determined from an experiment using a thin board.

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“…For a full characterising of the orthotropic time dependent behaviour, nine independent creep or relaxation functions are necessary. To determine these functions, laborious experimentations work should be performed (Schniewind and Barrett 1972;Cariou 1987;Hayashi et al 1993).…”

Section: Characterisation Of the Linear Behaviour Of Wood Viscoelastimentioning

confidence: 99%

Micromechanics of creep and relaxation of wood. A review COST Action E35 2004–2008: Wood machining – micromechanics and fracture

Navi

Stanzl-Tschegg

2008

HFSG

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Wood, like all polymeric materials, shows viscoelastic behaviour. The time dependent behaviour of wood depends on material anisotropy, temperature, moisture and stresses. To predict the behaviour of wood, numerous mathematical models have been developed largely relying on experimental results. In this paper, time dependent viscoelastic behaviour of wood is reviewed under constant and cyclic climatic conditions, separately. More emphasis is given on results obtained in recent years on the behaviour of thin wood tissues, single fibres, thermo-viscoelasticity of wood, influence of hemicelluloses and the modelling of the effect of transient moisture at the molecular level on the mechanical response.

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Wood as a linear orthotropic viscoelastic material

Cited by 95 publications

References 9 publications

Rheological behavior of wood in stress relaxation under compression

Rheological behavior of wood in stress relaxation under compression

Hygromorphic response dynamics of oak: towards accelerated material characterization

Micromechanics of creep and relaxation of wood. A review COST Action E35 2004–2008: Wood machining – micromechanics and fracture

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