L5 Notes

Stress

It is a value which describes the amount of applied force F (eg.,tensile, compressive, shear) carried by each unit of cross sectional area of a component. It is presented as "force per unit area".

Normal Stress Expressed as

σ = Fn / A

– σ = normal stress [Pa or N/m^2]

– Fn = normal component force [N]

– A = cross section area of the plane [m^2]

Shear Stress

τ = Fs / A

– τ = shear stress [Pa or N/m^2]

– Fs = Shear force, component force parallel to the surface [N]

– A = area of the plane [m^2]

F = weight (mg)

Strain

ε = x / L

x = Change of length [m]

L = Initial length [m]

Unit for strain ε

ε = ΔL / L

Young Modulas

Stress / Strain = constant

Modulus of Elasticity, E = stress / strain = (P / A) / (x / L) = PL / AX

P = load [N]

L = initial length [m]

A = cross section area [m2]

x = change in length [m]

Safety Factor

SF = Ultimate Stress / Allowable Stress (Design stress)

Ultimate stress = strength of material = strength of material , which is the maximum stress the material can take before it fractures.

• Allowable stress = design stress