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

Abstract 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.

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Time Dependent Viscoelastic Behaviour of EPS Geofoam

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.330.1095 ◽

2013 ◽

Vol 330 ◽

pp. 1095-1099 ◽

Cited By ~ 2

Author(s):

Yong Zou ◽

Chin Jian Leo ◽

Henry Wong

Keyword(s):

Power Law ◽

Elevated Temperatures ◽

Creep Behaviour ◽

Element Model ◽

Time Dependent ◽

Base Case ◽

Power Law Model ◽

Empirical Power ◽

Eps Geofoam ◽

Viscoelastic Models

A series of laboratory tests was carried out to assess the time-dependent creep behaviour of EPS geofoam at room temperature (23°C) and at 40°C. The experimental data were then used to calibrate and to validate mechanical viscoelastic models along with an empirical Power Law model, at these two temperatures. The viscoelastic models examined were the 3-element (Maxwell-Kelvin), the 4-element (Burgers) and the Modified 4-element models. The modified 4-element model and the base case, the empirical power law model, were found to give the best predictions. As anticipated, the experimental results show that creep rate is higher at elevated temperatures. The results, at 23°C and 40°C, offer a means to assess and model creep behavior in geotechnical applications at normal, and at a practical elevated, temperature where use of EPS geofoam in warmer climate may be a concern.

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Viscoelastic behaviour of solid wood under compressive loading

Holzforschung ◽

10.1515/hf.2006.047 ◽

2006 ◽

Vol 60 (3) ◽

pp. 294-298 ◽

Cited By ~ 9

Author(s):

Anjaneya Prasad Penneru ◽

Krishnan Jayaraman ◽

Debes Bhattacharyya

Keyword(s):

Compressive Loading ◽

Radiata Pine ◽

Solid Wood ◽

Time Dependent ◽

Viscoelastic Behaviour ◽

Wood Panels ◽

Relaxation Experiments ◽

Pattern Forming ◽

Inexpensive Procedure ◽

Good Agreement

Abstract To understand the mechanism of bulk wood forming, compressive stress relaxation experiments were performed on radiata pine (Pinus radiata D. Don) specimens with various moisture contents at a temperature of 200°C. The results aided in understanding the time-dependent viscoelastic behaviour with respect to springback and microstructural changes. This study clearly demonstrates the commercial feasibility of value-adding applications such as pattern forming on wood panels using a relatively simple, quick and inexpensive procedure. The experimental data were characterised by a three-component model with a spring and a Maxwell element in parallel, which showed very good agreement under different forming conditions.

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Influence of moisture content on the results of penetration and withdrawal resistance measurements on softwoods

Holzforschung ◽

10.1515/hf-2017-0133 ◽

2018 ◽

Vol 72 (7) ◽

pp. 549-555 ◽

Cited By ~ 10

Author(s):

Daniel F. Llana ◽

Eva Hermoso ◽

Ignacio Bobadilla ◽

Guillermo Iñiguez-Gonzalez

Keyword(s):

Moisture Content ◽

Penetration Resistance ◽

Radiata Pine ◽

Fiber Saturation Point ◽

Correction Factors ◽

Timber Structures ◽

Saturation Point ◽

Needle Penetration ◽

Screw Withdrawal ◽

Accuracy Of Results

AbstractNeedle penetration resistance (NPR) and screw withdrawal resistance (SWR) are widely used techniques for density estimation of woods integrated in timber structures. The moisture content (MC) influences these measurements and correction coefficients are needed to ensure the accuracy of results. The goal of the present paper was to scrutinize the relation between NPR and SWR measurements and MC in case of radiata pine, Scots pine, Salzmann pine, and maritime pine usually used in wood constructions, from which 25 specimens from each species were probed. The specimen’s MC ranged from 65.1 to 8.3%. Results show that NPR depth has a positive linear relationship with MC while the SWR force a negative one below the fiber saturation point (FSP). Above the FSP, the MC influence is less pronounced and less regular. MC correction factors of measurements below the FSP are proposed for the species studied.

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