A model for predicting the mechanical properties of wood-plastic composites : a micro-mechanical approach

Abstract

The development of a new composite that is compounded of natural fibres and low price polymers such as HDPE or PP began in the 90’s of the past century. Because this material is rather new on the market and due to random characteristics of the fibres no attempts have been made to analytically define the mechanical properties of this material. In this article the micromechanical approach called the Generalised Method of Cells (GMC) is introduced to describe the properties of injection moulded wood-plastic composites compounded of polypropylene (PP) or polystyrene (PS) and of wood or cellulose short fibbers. The main problem of analytical approach is that natural fibbers are not uniform in shape and size, which makes them hard to fit into the standard mathematical models. In this article average values of fibre size have been used. Materials were first scanned with optical and electron microscope to determine the fibre properties and their scatter. These values were then used in determining elastic and plastic response of the composite alongside with the maximum strength and elongation of the composite where the Tsai-Hill failure criterion was used. The results were then compared to the experimental data in order to evaluate the practical usefulness of this method.