What is stress concentration and how is it addressed in aircraft design?

Stress concentration occurs when local geometry (holes, notches, corners, thickness changes) causes stress to increase above the nominal value. The stress concentration factor Kt can be 2-5 or higher depending on geometry. In aircraft design, stress concentrations are addressed by: using generous fillet radii, proper hole edge distances, gradual thickness transitions, avoiding abrupt geometry changes, and fatigue-rated fastener installations. Fatigue analysis uses notch factors (Kf < Kt) accounting for material sensitivity. Critical areas like window corners and fastener holes require special attention.