Rheological behavior of wood in stress relaxation under compression

Abstract

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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“…The deformation rate for all investigated prisms was 1.5 mm/min (Nilsson & Johansson, 2019;Huč et al, 2018;Zakic, 1974). The samples were tested by axial compression along the fibres untill their complete destruction (Rabko et al, 2021;Pysarenko, 1988;.…”

Prediction of Mechanical Performance of Acetylated MDF at Different Humid Conditions

“…A better solution here is to use the help of micromechanical modelling approaches to specify material behaviour on a constituent level that is summarized in [32,54,55], and that will provide more reliable results compared with experimental ones and reduce the need for new sets of tests. More precisely, the employment of concurrent material and structural design applying multiscale models comes in since viscoelastic creep damage models and rheological behavior of MDF material are considered [56]. Here, we mean the time-dependent mechanical repose of MDF on a constant load considering the influence material´s density as well as fiber orientation, and the existence of voids and interfaces in the material microstructure.…”

Effect of compression parameters on stress relaxation behavior of bamboo fiber reinforced polypropylene composites

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