Stress Concentration

Key Concepts: Real structures may contain holes, fillets, corners, and sharp changes of section. In these cases the standard approximations leading to the formulas for nominal
stress and strain underestimate the actual values of stress and strain. Stress concentration factors (factors of "ignorance") may be used to obtain improved values for actual stress
and strain.

In a Nut Shell: Structures undergoing tension, torsion, and/or bending frequently have
interconnecting parts using welds and/or fasteners. Consequently, experimental techniques
are used to determine a stress concentration factor to account for a significant increase in
the level of stress at localized areas compared to the nominal stress. The table below shows the general form to relate the “actual” or maximum stress to the nominal or average stress.

σ_max = K σ_ave

and

τ_max = K τ_ave

where

σ_max is the maximum axial or bending stress at the location of stress concentration

τ_max is the maximum shear stress at the location of stress concentration

σ_ave is the axial or bending stress calculated from the usual formulas from

solid mechanics such as

σ_ave = P/A for axial loading

σ_ave = Mc/I for bending loads

τ_ave is the shearing stress calculated from the usual formulas from

solid mechanics such as

τ_ave = Tc/J for torsional loading

and K is the stress concentration factor determined from experimental data

in the form of charts

Click here for examples.

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