Stress Concentration at a Circular Hole
Holes, notches, and other geometric discontinuities cause local stress to rise well above the nominal (average) stress. This local peak-to-nominal ratio is the stress concentration factor, Kt. For a finite-width flat plate with a central circular hole under axial tension, a well-known polynomial approximation is Kt = 3 − 3.14(d/W) + 3.667(d/W)2 − 1.527(d/W)3, where d is hole diameter and W is plate width.
For an infinitely wide plate (d/W approaching 0), this reduces to the classic textbook value Kt = 3. As the hole grows relative to the plate width, Kt decreases from this theoretical maximum. This is used for general design estimation; precise analysis for critical components should use finite element analysis or detailed reference charts.
Last reviewed August 2026