Stress-Strain Curves

As we have previous 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 through laboratory tests. Let us assume one such test so that you might understand certain mechanical properties of solids.

Tension Test on a Mild Steel Rod

A mild steel rod of known diameter & length of approximate 400 mm to 500 mm is firmly gripped in a universal testing machine & 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 any point is indicated by the load dial of the UTM when the elongation of the bar over the gauge length is measured through the deformeter.

The load is slowly applied on the bar in appropriate increments and the corresponding elongations of the bar are calculated at each stage. The test is carried out till the specimen finally fails by rupture. The load values at each of stage are divided by the cross sectional area of the bar to get the stress values and the equivalent elongations of the bar divided by the gauge length give the strain values. A graph is drawn associating stress and corresponding strain.