Viscoelastic behaviour of green wood across the grain. Part II. A temperature dependent constitutive model defined by inverse method

Abstract

This paper proposes a new inverse method to identify Kelvin's elements simultaneously from several creep tests carried out at different temperature levels. The dimensionless formulation derived for this approach allows thermally activated Kelvin's elements to be used on non-isothermal tests. For each studied species and each material direction, four different tests are analysed simultaneously to define the parameters of the constitutive model. Each test comprises a linear increase in temperature, a plateau at the desired temperature (65°C, 85°C, 105°C and 1207deg;C respectively) and a final cooling period. The paper ends up with a comprehensive viscoelastic characterisation of oak and spruce in radial and tangential directions, over a temperature range spreading from 40°C to 120°C. Five Kelvin's elements were required for spruce and four elements for oak. Such models are intended to be used in the simulation of wood processing operations, such as drying, steaming, thermal treatment... © INRA, EDP Sciences, 2005.