Stress and strain

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Description Symbol Name Units
Direct stress σ Sigma N/m² and
N/mm²
Direct strain ε Epsilon None
Shear stress τ Tau N/m² and
N/mm²
Young’s modulus
of elasticity
E N/m² and
N/mm²
Home Stress and strain
Symbols and units
The table below identifies the symbols and units used in the
calculation of stress and strain.
Note: 1N/mm² = 10⁶N/m² = 1MN/m²
And 1kN/mm² = 1GN/m²
The alternative for stress is the pascal (pa)which equals 1 N/m²
Two effects may be identified, when the force acts on a solid
material which remains stationary.
The material will:­
Exert an internal resisting force known as a state of stress;
Experience dimensional changes
This behaviour is typical of stressed engineering components but the
dimensional changes are usually small are not normally seen with the
naked eye.
Direct forces
One end of a bar may be subjected to push or pull. Now, if a bar
remains stationary, a pull on one end must result in an equal and
opposite pull on the other end, and the bar is said to be in tension.
Similarly, a push on one end is accompanied by a push on the other
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end, and the bar is in compression.
The forces which are producing a tension or compression are called
direct forces.
Also, direct forces are called either tensile (A pull) or compressive (A
push).
Tensile forces cause a bar to stretch and compressive forces cause a
bar to contract.
Fig 1
Fig 1 Illustrates a bar acted upon by a tensile force at either end
causing the bar to stretch.
F = The applied force
A = Cross sectional area of the bar
L = Original length of the bar
x = Change in length produced by the applied force, F
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