Abstract
In order to elucidate the effects of moisture content on the strain energy to the proportional limit Up and that to the maximum load Um, the mechanical characteristics (σp, εp: stress and strain at the proportional limit, E: modulus of elasticity in bending, σm, εm: stress and strain at the maximum load) in bending were determined by the central loading on beams of Sitka spruce (Picea sitchensis CARR.). The measurements were carried out at 20, 30, 40 and 50°C under the nominal moisture content of 0, 5, 10 and 15%.
The strain energy to the proportional limit Up and that to the maximum load Um were calculated by finding the respective areas under the load-deflection curve and dividing them by the volume of the span portion of beam.
The results obtained are as follows:
(1) The values of σp, σm, εp and E decreased almost linearly, and the value of εm increased, with the increase of moisture content.
(2) The strain energies of Up and Um decreased almost linearly with the increase of moisture content.
(3) The change of Up and Um with moisture content was dependent on the relative relation between the percentage change of stress and strain corresponding to the 1% change in moisture content. In this experiment, the average percentage change in stress (σp, σm) with the 1% change in moisture content was more than that in strain (εp, εm).
