Modelling of Stiffness and Hygroexpansion of Wood Fibre Composites

• Paper 1The eld of research involving the analytical modelling of the stiff ness and hygroexpansion of composite material is reviewed. This paper can be regarded as an introduction to the area of the mechanics of composite materials in general and to wood fibre composites in particular. The most important models, such as the Reuss and Voigt bounds and the Halpin-Tsai, are described, along with their advantages and limitations. The report also contains examples ofcalculations made for various models, allowing them to be compared.Paper 2In this paper, coordinate transformations of the stresses, strains and stiffness of composite materials are described. A new method for interpolating between the extremes of homogeneous strain and homogeneous stress for calculating the stiffness matrix of composites is introduced. This new interpolation method is shown by use of advanced matrix theory, to be coordinate independent.Paper 3A 3D analytical model for stiffness and hygroexpansion is presented. The model involves two steps. The first step is the homogenisation of a structure composed of a single wood fibre coated by a layer of matrix material. The second step is the integration of the various fibre orientations involving a linear and an exponential interpolation between an extreme case of homogenous strain and an extreme case of homogenous stress. A comparison is made between the prediction as modelled and measurement data for stiffness, Poisson's ratio andhygroexpansion. The matrix material is assumed to have isotropic properties, whereas the fibres and the particle material can have arbitrary orthotropic properties. The model can be used for all volume fractions and is also valid for particle composites.Paper 4This paper presents a 3D numerical model for the stiffness and hygroexpansion properties of wood fibre composite materials. The microstructure of a composite composed of a number of fibres is modelled by use of a fibre geometry preprocessor. The model is employed for analysing the mechanical behaviour of wood fibre composites that have bre network geometries. Results obtained by use of the model are compared with results based on the analytical model presented in paper 3 and with various test results.

• Paper 1The field of research involving the analytical modelling of the stiff ness and hygroexpansion of composite material is reviewed. This paper can be regarded as an introduction to the area of the mechanics of composite materials in general and to wood bre composites in particular. The most important models, such as the Reuss and Voigt bounds and the Halpin-Tsai, are described, along with their advantages and limitations. The report also contains examples ofcalculations made for various models, allowing them to be compared.Paper 2In this paper, coordinate transformations of the stresses, strains and stiffness of composite materials are described. A new method for interpolating between the extremes of homogeneous strain and homogeneous stress for calculating the stiffness matrix of composites is introduced. This new interpolation method is shown by use of advanced matrix theory, to be coordinate independent.Paper 3 A3D analytical model for stiffness and hygroexpansion is presented. The model involves two steps. The first step is the homogenisation of a structure composed of a single wood bre coated by a layer of matrix material. The second step is the integration of the various fibre orientations involving a linear and an exponential interpolation between an extreme case of homogenous strain and an extreme case of homogenous stress. A comparison is made between the prediction as modelled and measurement data for stiffness, Poisson's ratio and hygroexpansion. The matrix material is assumed to have isotropic properties, whereas the fibres and the particle material can have arbitrary orthotropic properties. The model can be used for all volume fractions and is also valid for particle composites.Paper 4This paper presents a 3D numerical model for the stiness and hygroexpansion properties of wood bre composite materials. The microstructure of a composite composed of a number of bres is modelled by use of a fibre geometry preprocessor. The model is employed for analysing the mechanical behaviour of wood fibre composites that have fibre network geometries. Results obtained by use of the model are compared with results based on the analytical model presented in paper 3 and with various test results.

Subject headings

LANTBRUKSVETENSKAPER  -- Lantbruksvetenskap, skogsbruk och fiske -- Trävetenskap (hsv//swe)

AGRICULTURAL SCIENCES  -- Agriculture, Forestry and Fisheries -- Wood Science (hsv//eng)

Publication and Content Type

lic (subject category)

vet (subject category)