The viscoelastic behaviour of wood under compressive stress

Abstract

The behaviour of wood under mechanical stress is both time-dependent and sensitive to temperature and moisture content. Whilst the prediction of such behaviour is desirable, existing models , often represented by mechanical analogues designed only to imitate the observed time-dependency, fail to describe the mechanisms responsib1e for "creep" . In consequence these ana1ogues display no inherent sensitivity to environmental conditions. The purpose of this research was to demonstrate this sensitivity experimentally (in particular, to the effects of wood temperature and moisture content), and to devise a model based on the behaviour of bonding systems known to exist in wood , which as well as describing the time-dependency , could also cater for the effects of temperature and moisture content.
Small pieces of isolated Sitka spruce (Piceasitchensis) earlywood were loaded in compression in the radial direction . Deformation under load , and recovery after load removal , were recorded using a linear voltage transducer linked to a microcomputer. The behaviour was recorded at different temperatures between 30° C and 90°C, and at a series of wood moisture contents between 0% and "green". The loading and recovery periods were 6 hours each.
A model of the time-dependent behaviour of wood under mechanical stress is proposed, and its ability to simulate observed phenomena is discussed.

Date of Award	Jun 1992
Original language	English
Awarding Institution	University of Wales, Bangor
Sponsors	Science and Engineering Research Council