What is stress concentration and how is it handled in design?

Stress concentration occurs at geometric discontinuities (holes, notches, fillets) where actual stress exceeds nominal stress by factor Kt. σmax = Kt × σnominal, where Kt depends on geometry and can range from 1.5-3 or higher. Design solutions include adding fillets, gradual transitions, surface treatments, or using materials with better fatigue resistance. FEA accurately captures these effects.