Location as a factor affecting material properties

By assuming a material as continuum, the variation in properties at different locations on the material is solely dependent on its uniformity. The uniformity of a material is defined by the consistency in term of its composition at any point.

Heterogeneous Material

A heterogeneous material shows a distinctive composition at the microscopic level, at any location on it. Since all constituent materials are not evenly distributed over the material, its properties are said to be dependent on the location on the material.

An example for heterogeneous material is reinforced concrete, which is a composite consisting of two main construction materials: concrete and steel.

The dominant constituent material, concrete, shows good compression but poor tension. On the other hand, steel shows good tension, but its strength declines tremendously after being subjected to very high temperature and corrosion.

The combination of concrete and steel, i.e. reinforced concrete, is an economical solution to improving the structural member’s resistance to compression, tension, bending and shear.

For example, when load is applied on the top of a beam, a sagging moment is induced. The top of the beam is subjected to compression, while the bottom is subjected to tension. The primary reinforcing steel bars are placed at the bottom of the beam to help resist the tension. Concrete is casted around the steel bars to hold them in place and provide protection against high temperature and corrosion.

Consider that the tension is applied at two different locations on a reinforced concrete, as shown in Fig. 1.3 below. Due to the difference in composition at different locations, the material’s behaviour varies at the point that consists of concrete only; the deformation there is significantly higher than that at the point that consists of both concrete and steel.

Homogeneous Material

An ideal homogeneous material shows a uniform composition at the microscopic level, at any location on it. Since all constituent materials are well-distributed over the material, its properties are said to be independent of the location on the material.

An example of a homogeneous material is stainless steel. Its constituent materials are iron ore, chromium, silicon, nickel, carbon, manganese and nitrogen. The first step in manufacturing stainless steel is heating the constituent materials, melting them and letting them mix. The process is important to ensure the final product is homogeneous. Fig. 1.4 shows the steel manufacturing process as described above.

FIGURE 1.4 Hot-rolled and cold-rolled steel manufacturing process.