Hygromechanical strains during the drying of Eucalyptus nitens boards

N Pérez-Peña,C Salinas-Lira,D.M Elustondo,R A Ananías,A Cloutier,L Salvo-Sepúlveda,V Sepúlveda-Villarroel,F Segovia

doi:10.4067/s0718-221x2016005000021

N Pérez-Peña, C Salinas-Lira + Show 6 more

Open Access

https://doi.org/10.4067/s0718-221x2016005000021

Copy DOI

Abstract

Collapse and drying stresses are currently induced during the drying of Eucalyptus nitens in solid wood products. The purpose of this study was to investigate these drying stresses by measuring hygromechanical strains during the drying of Eucalyptus nitens boards. Small samples of Eucalyptus nitens wood were oriented in the radial and tangential directions and tested to determine the hygromechanical strains during the drying process. This experimental work consisted of cantilevered bending tests conducted under variable relative humidity conditions. Tests were performed in a conditioning chamber at 30 °C with an equilibrium moisture content ranging from 22 to 12% under four levels of stress: 0, 10, 20 and 30% of the rupture load. The strains were determined using strain gauges, and the total deflection was measured with a linear variable differential transformer. The results show that in hygromechanical strains during the drying of Eucalyptus nitens, both the surface deformation and mechano-sorption strain were found to be proportional to the applied stress and reached their maximum values in the tangential direction. The total deflection increased 0,18 mm/mm with a surface deformation of 0,20 mm/mm, and the mechano-sorptive strain provides a greater contribution with a value of 0,11 mm/mm, thus corresponding to 59% of the total deformation. In attempts to improve the drying schedules of Eucalyptus nitens to develop solid wood products, mechano-sorptive behavior may be applied to relieve collapse and drying stress.

Highlights

The complex mechanical behavior of wood should be considered to understand wood behavior during the drying and desorption processes
Shrinkage begins to develop on the wood surface when the moisture content (MC) decreases below the fiber saturation point (FSP), and the shrinkage is restrained by the internal region that remains above the FSP
After the first change in relative humidity (RH), when the wood moisture content decreased from 22% to 17%, the surface deformation increased rapidly, demonstrating the occurrence of MS deformation and coincides with the description of the phenomenon of mechano-sorptive creep that consists in an increase of creep deformation during any desorption (Hunt and Shelton 1988)

Summary

Introduction

The complex mechanical behavior of wood should be considered to understand wood behavior during the drying and desorption processes. It has been demonstrated that the mechanical behavior during wood drying is strongly dependent on temperature, relative humidity, time and applied load, among others factors (Moutee et al 2010). Wood experiences differential shrinkage between the surface and the core, which induces the development of mechanical stresses. Shrinkage begins to develop on the wood surface when the moisture content (MC) decreases below the fiber saturation point (FSP), and the shrinkage is restrained by the internal region that remains above the FSP. The external surfaces generate tension in the direction of the undeveloped shrinkage, placing the internal regions under compression and generating tension in the opposite direction (Salinas et al 2015)

Objectives

Methods

Results

Conclusion