TENSILE STRESS AND STRAIN
When a body is subjected to two equal and opposite axial pulls P (also called tensile load) as shown in Fig. 1 (a), then the stress induced at any section of the body is known as tensile stress as shown in Fig. 1 (b). A little consideration will show that due to the tensile load, there will be a decrease in cross-sectional area and an increase in length of the body. The ratio of the increase in length to the original length is known as tensile strain.
Let, P = Axial tensile force acting on the body,
A = Cross-sectional area of the body,
l = Original length, and
δl = Increase in length.
∴ Tensile stress, σt = P/A
and tensile strain, ε t = δl / l
A textbook of Machine Design by R.S.Khurmi and J.K.Gupta