Orientation as a factor affecting material properties

A material’s behaviour also depends on its orientation with respect to the applied force. Ideally, a material is assumed isotropic to simplify engineering analysis and design. However, this is nearly impossible in the real world, as a perfect homogeneous material is impossible to be created.

Due to the imperfect uniformity in term of composition, the material will react differently to the same magnitude of force that acts along different directions.

Anisotropic Material

An anisotropic material shows six different mechanical properties when force is acting in six different directions along three mutually orthogonal axes, i.e. principal axes. In other words, its properties are dependent on the orientation of the material.

A composite is usually anisotropic. It is created by combining two or more constituent materials with different properties. The final material is created by arranging these constituent materials in either a specific or a vnon-specific order without breaking the arrangement of their particles. This makes the final material anisotropic, because the properties of each constituent material are only present throughout the space that such a constituent material occupies.

An example of a composite is fibre-reinforced concrete. In a fibre-reinforced concrete block, concrete provides principal resistance to compression, while fibre, e.g. synthetic fibre, provides principal resistance to tension. Fibre is an anisotropic material. It shows highest resistance to tension only when the force is acting along its longitudinal axis. Therefore, the orientation and arrangement of fibre directly affect the tensile strength of the concrete.

In a fibre-reinforced concrete block, the arrangement and orientation of constituent materials, aggregates, sand, cement (components of concrete) and fibres are always arbitrary in every direction. This causes the tensile strength of fibre- reinforced concrete to vary in different directions, as shown in Fig. 1.5.