Polymer–wood fibre composites utilize wood fibres as reinforcing filler in the polymer matrix and are advantageous over the pure polymers in terms of the materials cost and some mechanical properties such as modulus and strength. The scope of the present paper is to study the prospects of using wheat straw fibres as a reinforcing filler in polypropylene (PP). Untreated and silane-treated fibres having a variety of fibre lengths were used at various fibre contents to reinforce PP. Composites were tested for their mechanical, thermal and rheological properties, and the assessment of the adhesion at the interface was made via observations by SEM microscopy. The results showed that for untreated fibres, an increase in fibre content up to 20% (wt) led to an increase in the tensile strength of the composite. However, beyond this amount, tensile strength decreased. On the other hand, the tensile modulus increased due to higher stiffness of the fibres. By using silane treated fibres, both tensile strength and modulus increased, but the viscosity was reduced because of better dispersion of the treated fibres. By the addition of nano-clay, the mechanical properties of the composites, compared to the pure polymer, increased up to a certain fibre content, and after that the trend was reversed.

The relation between hardness, strain and temperature has been widely investigated over the past decades. However, less attention has been paid to the effect of strain rate on hardness induced in high rate deformations. In this investigation, the relation between strain, temperature and strain rate is studied and a new model is proposed. The investigation is performed by experiment and numerical simulation. The simulations are used to predict the distribution of the strain and strain rate within the specimen. The high rate experiments are conducted using Taylor test, compressive and tensile Hopkinson bar. Quasi-static tests are also carried out using Instron testing machine. The results show a quadratic relation between the hardness and strain rate. The results also indicate that the relation between hardness, strain and temperature is the same for the compressive and tensile loading but the relation between hardness and strain rate is different for the compression and tension. The hardness increases with the increase of the strain and strain rate but decreases with the temperature. The reason is believed to be due to dislocation pile up which is denser in compression than that in tension.

A new anisotropic constitutive model for granular materials is developed. This model exhibits the noncoaxiality of the principal axes of stress and strain rate as a natural consequence of a kinematic hypothesis. A fabric reconstruction parameter ℬ plays an important role in this model. The pressure sensitivity parameter, μ, and two different hardening parameters often employed in modeling granular materials, come out to be expressible in terms of this fabric reconstruction factor. The stress criterion in this model is not friction based, and therefore the rolling of granules can be taken into account through the fabric paramater. Numerical results are presented on the basis of a phenomenological trial function for ℬ.