Mechanical Behaviour of Materials:

Stress-Strain Curves

As we have previously observed, the behaviour of solids, while subjected to loads, depends upon its mechanical and geometrical properties. The mechanical properties of solids have to be investigated by laboratory tests. Let us consider one such test so that you can know certain mechanical properties of solids.

Tension Test on a Mild Steel Rod

A mild steel rod of known length and diameter of about 400 mm to 500 mm is firmly gripped within a universal testing machine and a deformeter is fixed on the rod over a measured gauge of 150 mm to 200 mm. The rod is subjected to axial tensile load. The load at some instant is denoted through the load dial of the UTM although the elongation of the bar over the gauge length is measured by the deformeter.

The load is gradually applied on the bar in appropriate increments and the corresponding elongations of the bar are measured at every stage. The test is carried out until the specimen ultimately fails through rupture. The loads values at each stage are divided through the cross sectional area of the bar to get the stress values and the corresponding elongations of the bar divided through the gauge length provide the strain values. A graph is drawn relating stress and corresponding strain. A classical stress- strain curve for mild steel is display in Figure.

Figure: Stress-Strain Curve for Mild Steel