Erik Marklund

Nonlinear Viscoelasticity and Viscoplasticity of Flax/Polypropylene Composites

In tensile tests the flax/polypropylene composites clearly show nonlinear behavior in loading and hysteresis loops in unloading. In creep tests performed at different load levels the response was n ...

Stiffness of Aligned Wood Fiber Composites : Effect of Microstructure and Phase Properties

The effect of wood fiber anisotropy and their geometrical features on wood fiber composite stiffness is analyzed. An analytical model for an N-phase composite with orthotropic properties of constituents is developed and used. This model is a straightforward generalization of Hashins concentric cylinder assembly model and Christensens generalized self-consistent approach. It was found that most macro-properties are governed by only one property of the cell wall which is very important in attempts to back-calculate the fiber properties. The role of lumen (whether it filled by resin or not) has a very large effect on the composite shear properties. It is shown that several of the unknown anisotropic constants characterizing wood fiber are not affecting the stiffness significantly and rough assumptions regarding their value would suffice. The errors introduced by application of the Hashins model and neglecting the orthotropic nature of the material behavior in cylindrical axes are evaluated. The effect of geometrical deviations from circular cross-section, representing, for example, collapsed fibers, is analyzed using the finite element method (FEM) and the observed trends are discussed.

Modelling stiffness and strength of non-crimp fabric composites: semi-laminar analysis

Abstract: In this chapter, engineering models based on semi-laminar considerations, particularly considering features on the mesoscale, for computation of non-crimp fabric composite stiffness are addressed. Both analytical and finite element models are employed on different scales in the material. Thereafter, engineering models based on laminate considerations with simplistic descriptions of the mesoscale features for strength modelling are presented.

Effective stiffness of curved 0°-layers for stiffness determination of cross-ply non-crimp fabric composites

The effect of the 0°-tow waviness on axial stiffness of cross-ply non-crimp fabric composites is analysed using multiscale approach. The curved 0°- and 90°-layers are represented by flat layers with effective stiffness properties and classical laminate theory is used to calculate the macroscopic stiffness. The effective 0°-layer stiffness is calculated analysing isolated curved 0°-layers subjected not only to end loading, but also to surface loads. The surface loads are identified in a detailed finite element analysis and approximated by a sinus shaped function with amplitude depending on the waves parameters. The sinus shaped surface loads are then applied to an isolated curved 0°-layer finite element model together with end loading to calculate the effective stiffness of the layer. Finally, the effective 0°-layer stiffness was successfully used to calculate the macroscopic stiffness of the composite proving validity of the approach being used and showing that, without losing accuracy, elastic properties in the 90°-layers with bundle structure can be replaced by the transverse stiffness of the homogenised 90°-layer material.

Micromechanical modelling of wood fibre composites

Abstract A concentric cylinder model for an N-phase composite with orthotropic properties of constituents was previously presented by the authors. With only minor modifications the model allows for including also free hygroexpansion terms in the elastic stress–strain relationship in order to deal with orthotropic phase swelling. Thus the effect of wood fibre ultrastructure and cell wall hygroelastic properties on wood fibre composite hygroexpansion may be analysed. Multiscale modelling was performed to calculate the hygroexpansion coefficients of both the fibre cell wall and the aligned wood fibre composite. Furthermore, the fibres helical structure leads to an extension–twist coupling and thus a free fibre will deform axially and also rotate upon loading in longitudinal fibre direction. Within the composite, however, the fibre rotation will be restricted. Therefore, the decision was to compare the composite performance in the two extreme cases (i) free rotation (ii) no rotation of the fibre in the composite.

FLOAT-SINK SEPARATION OF CONSTRUCTION AND DEMOLITION WASTE FINES

Landfilling and waste incineration are two major waste management options. However, due to their carbon content, some wastes may be unsuitable for these systems. Therefore, methods capable of removing organic carbon from wastes should be identified. One of these wastes is represented by construction and demolition fines. In this paper, we investigate the use of water in separating the waste by density, to verify the suitability of this method in the separation of carbon-containing materials, both in lab and field scale tests. The results obtained show that half of the carbon (measured as volatile solids) can be separated. However, this method fails to reliably produce a sink fraction suitable for landfilling, as it continues to be characterized by an excessively high organic material content.

Multiscale Modelling of Non-Crimp Fabric Composites

Damage initiation and evolution in NCF composites leading to final failure includes a multitude of mechanisms and phenomena on several length scales. From an engineering point-of-view a computation ...