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Publications (5 of 5) Show all publications
Huč, S. & Svensson, S. (2018). Coupled two-dimensional modeling of viscoelastic creep of wood. Wood Science and Technology, 52(1), 29-43
Open this publication in new window or tab >>Coupled two-dimensional modeling of viscoelastic creep of wood
2018 (English)In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 52, no 1, p. 29-43Article in journal (Refereed) Published
Abstract [en]

Three coupled two-dimensional viscoelastic creep models for orthotropic material are analyzed. The models of different complexity are mathematically formulated and implemented in a finite element software. Required viscoelastic material parameters are determined by calibration procedure, where numerical results are compared against experimentally obtained viscoelastic strains caused by tensile or shear loading. Finally, a comparison method is used to evaluate the accuracy of strain predictions of each particular model. The analysis shows that all the models are able to accurately predict viscoelastic creep simultaneously in two perpendicular directions for various periods of time and wood species. Calculated numerical values of the viscoelastic material parameters suitable for the three models and wood species, i.e., Douglas fir (Pseudotsuga menziesii), Norway spruce (Picea abies), Japanese cypress (Chamaecyparis obtusa), and European beech (Fagus sylvatica L.), under constant tensile loading are also given.

Place, publisher, year, edition, pages
Springer, 2018
Keywords
time-dependence, deformation kinetics, rheological model, chemical-kinetics, grain
National Category
Other Civil Engineering
Identifiers
urn:nbn:se:hb:diva-13637 (URN)10.1007/s00226-017-0944-3 (DOI)000419587400002 ()2-s2.0-85028327918 (Scopus ID)
Available from: 2018-02-09 Created: 2018-02-09 Last updated: 2018-02-13Bibliographically approved
Huč, S., Svensson, S. & Hozjan, T. (2018). Hygro-mechanical analysis of wood subjected to constant mechanical load and varying relative humidity. Holzforschung, 72(10), 863-870
Open this publication in new window or tab >>Hygro-mechanical analysis of wood subjected to constant mechanical load and varying relative humidity
2018 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 72, no 10, p. 863-870Article in journal (Refereed) Published
Abstract [en]

A hygro-mechanical (H-M) analysis of a wooden specimen sustaining a mechanical load while subjected to varying relative humidity was performed to predict the long-term rheological behavior of wood. The numerical analysis was based on the experimental results of total strains, monitored in two orthotropic material directions on oak wood specimens under constant uniaxial compression and with moisture content (MC) variation. For the moisture analysis, a multi-Fickian moisture transport model (MFMTM) was used to obtain temporal and spatial MC fields, which were the input data in the mechanical analysis. The presented mechanical model assumed a decomposition of the total strains into the elastic, viscoelastic and mechanosorptive strains and the strains due to shrinkage and swelling. The moisture and mechanical analyses required material parameters, which were taken from the literature or were empirically obtained by a fitting procedure. The performed H-M analysis gave accurate numerical predictions of the experimentally obtained total strains in two orthotropic directions simultaneously. Thus, the analysis developed has a high potential for predicting the long-term rheological behavior of timber structures, assuming that the material parameters are determined previously, based on specific, extensive, multidimensional experimental analyses.

Keywords
compression perpendicular to grain, mechanical model, mechanosorption, multi-Fickian moisture transport model, varying climate conditions, viscoelasticity, wood
National Category
Applied Mechanics
Identifiers
urn:nbn:se:hb:diva-15140 (URN)10.1515/hf-2018-0035 (DOI)000445777000005 ()2-s2.0-85048831362 (Scopus ID)
Available from: 2018-10-02 Created: 2018-10-02 Last updated: 2018-11-30Bibliographically approved
Huč, S. & Svensson, S. (2018). Influence of grain direction on the time-dependent behavior of wood analyzed by a 3D rheological model. A mathematical consideration. Holzforschung, 72(10), 889-897
Open this publication in new window or tab >>Influence of grain direction on the time-dependent behavior of wood analyzed by a 3D rheological model. A mathematical consideration
2018 (English)In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 72, no 10, p. 889-897Article in journal (Refereed) Published
Abstract [en]

A three-dimensional (3D) rheological model for an orthotropic material subjected to sustained load or deformation under constant climate has been mathematically formulated. The elastic and viscoelastic compliance matrices are symmetric, where the mathematical derivation of the latter is shown. The model is linear and requires constant numerical values for the elastic and viscoelastic material parameters. The model’s ability to predict the natural time-dependent response in three material directions simultaneously is demonstrated on a Douglas fir (Pseudotsuga menziesii) specimen subjected to a constant uniaxial tensile load. The material extends in a longitudinal direction and contracts in the transverse directions with time. The required material parameters are taken from the literature when possible, otherwise they are assumed. Furthermore, the influence of misalignment between the directions of observation and wood material directions on induced time-dependent strains is analyzed. The analyses show that the misalignment has a large effect on the material behavior. In some cases, the specimen under constant uniaxial tension even extends in the perpendicular transverse direction with time. The obtained results clearly demonstrate the high importance of considering the alignment of material directions precisely in order to be able to interpret the time-dependent behavior of wood correctly.

Keywords
grain direction, linear elasticity, linear viscoelasticity, material orthotropy, symmetry of compliance matrix, three dimensional rheological model, uniaxial tension, wood
National Category
Applied Mechanics
Identifiers
urn:nbn:se:hb:diva-15139 (URN)10.1515/hf-2017-0180 (DOI)000445777000008 ()2-s2.0-85048772085 (Scopus ID)
Available from: 2018-10-02 Created: 2018-10-02 Last updated: 2018-11-30Bibliographically approved
Huč, S., Hozjan, T. & Svensson, S. (2018). Rheological behavior of wood in stress relaxation under compression. Wood Science and Technology
Open this publication in new window or tab >>Rheological behavior of wood in stress relaxation under compression
2018 (Swedish)In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225Article in journal (Refereed) Published
Abstract [en]

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

Place, publisher, year, edition, pages
Springer, 2018
National Category
Other Civil Engineering
Identifiers
urn:nbn:se:hb:diva-13638 (URN)10.1007/s00226-018-0993-2 (DOI)
Available from: 2018-02-10 Created: 2018-02-10 Last updated: 2018-02-13Bibliographically approved
Huč, S., Svensson, S. & Hozjan, T. Numerical analysis of moisture-induced strains and stresses in glued-laminated timber.
Open this publication in new window or tab >>Numerical analysis of moisture-induced strains and stresses in glued-laminated timber
(English)In: Article in journal (Refereed) Submitted
National Category
Applied Mechanics
Identifiers
urn:nbn:se:hb:diva-15653 (URN)
Available from: 2019-01-10 Created: 2019-01-10 Last updated: 2019-01-17
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-7658-4194

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