Stress and Strain Simple Explanation


Stress is defined as the force per unit area of a material.

Stress = force / cross sectional area

σc = P/A

Unit: N/mm2


Strain is defined as extension per unit length.

Strain = extension / original length

ԑc = δL/L

Unit: No unit

Example problem


A rectangular wooden column of length 3m and size 300mm x 200mm carries an axial load of 300kN. The column is found to be shortened by 1.5mm under the load. Find the stress and strain in the column.

Given data:

Original length of column (L) = 3m = 3000mm

Area of cross section (A) = 300 x 200 = 60000mm2

Axial Load (P) = 300kN = 300000N

Shortening of column (δL) = 1.5mm


Stress (σc) = ?

Strain (ԑc) = ?


Compressive stress σc = P/A

Compressive strain ԑc = δL/L


σc = P/A

= 300000/60000

= 5N/mm2

ԑc =  δL/L

= 1.5/3000

= 0.0005


Stress σc = 5N/mm2

Strain ԑc = 0.0005


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