Nonlinear tensile creep behavior of radiata pine at elevated temperatures and different moisture contents

• Published in: Holzforschung Vol. 69; no. 7; pp. 915 - 923
• Main Authors: Pearson, Hamish, Ormarsson, Sigurdur, Gabbitas, Brian
• Format: Journal Article
• Language: English
• Published: Berlin De Gruyter 01.09.2015; Walter de Gruyter GmbH
• Subjects: high temperature; material properties; moisture content; nonlinear creep; softening; tensile creeping; thermohygromechanical (THM); wood
• ISSN: 0018-3830; 1437-434X
• DOI: 10.1515/hf-2014-0240

Tensile wood creep has not been measured previously in the temperature region 135°C–150°C for a range of moisture content (MC) up to fiber saturation point due to equipment and measurement challenges. Yet this is the region where the most dramatic softening effects can be observed. The aim of this study was to develop specialized equipment to measure tensile solid wood creep over 70°C–150°C for a range of MC and loads. Creep displacement was successfully able to be isolated from elastic and mechanosorptive strains and statistically modeled by regression analysis. This proved more accurate than complex series expansions consisting of spring- and dashpot-type components. The best creep displacement relationship was a power law with a strain root mean square error of 0.28%. The amplitude of the power law was nonlinear with respect to stress and temperature and changed by a stress factor of up to 0.9 for a stress of up to 1.2 MPa and by a temperature factor 1.2–6.3 over the investigated range. The creep relationship provides a valuable tool for predicting time-dependent distortion and internal stress of wood during drying or thermohygromechanical modification below 150°C.