Stress & Strain
Stress is defined as “force per area” or an object’s internal resisting forces.
Stress normal to the plane is usually denoted as “normal stress” and can be expressed as
σ = Fn/A
where
σ = normal stress ((Pa) N/m2),
Fn = normal component force (N),
A = area (m2).
Stress parallel to the plane is usually denoted as “shear stress” and can be expressed as
τ = Fp/A
where
τ = shear stress ((Pa) N/m2, psi),
Fp = parallel component force (N, lbf ),
A = area (m2, in2).
Strain is defined as the displacement and deformation that occur due to stress. Strain can be expressed as:
ε = dl/lo
where
dl = change of length (m, in),
lo = initial length (m, in),
ε = unitless measure of engineering strain.