Micromechanics of creep and relaxation of wood. A review COST Action E35 2004–2008: Wood machining – micromechanics and fracture

Abstract

Wood, like all polymeric materials, shows viscoelastic behaviour. The time dependent behaviour of wood depends on material anisotropy, temperature, moisture and stresses. To predict the behaviour of wood, numerous mathematical models have been developed largely relying on experimental results. In this paper, time dependent viscoelastic behaviour of wood is reviewed under constant and cyclic climatic conditions, separately. More emphasis is given on results obtained in recent years on the behaviour of thin wood tissues, single fibres, thermo-viscoelasticity of wood, influence of hemicelluloses and the modelling of the effect of transient moisture at the molecular level on the mechanical response.

Creep behaviour of single hemp fibres. Part II: Influence of loading level, moisture content and moisture variation

“…The existence of a mechanosorptive (MCS) effect in hemp fibre remains an open query. Indeed, although the MCS effect has been studied since the late 1950s for wood and paper materials [3], the topic is highly contentious and there is no widely accepted explanation. Its existence for single fibres is widely debated in the scientific community since negative results have been published [4][5][6][7].…”

Tensile creep and recovery of Norway spruce influenced by temperature and moisture

“…A lower wood stiffness can also be achieved by increasing the temperature for wood at constant moisture content (Gerhards 1982 ). Also, the TDMB is infl uenced by moisture and temperature in that an increasing creep rate is observed when either moisture content (Kojima and Yamamoto 2005 ) or temperature (Navi and Stanzl -Tschegg 2009 ) is increased.…”

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“…Mechanical research into TW has until now mainly focused on the axial elastic modulus. However, wood, like other polymeric composite materials, displays viscoelastic behaviour (Navi and Stanzl-Tschegg 2009). By definition, the mechanical response of a viscoelastic material contains both elastic (instantaneous) and viscous (time-dependant) elements.…”