stress and strain and strain guage

Stress : Force that produces strain on a physical body.

stress= F/A
Stress (N/m2)
F: Force (N)
A: Area (m2)

Strain: Deformation of a physical body under the action of applied forces.

e= ΔL/L= L-L/L
e : strain

L= Original length
Δ= change in length

Strain guage:

It is a device used to measure the strain of an object। the most common type of strain gauge consists of an insulating flexible backing which supports a metallic foil pattern.