characteristic-crack-growth da / dN = Crack growth rateda / dN = C ( K )mK = . a m = tan log da/dNlog KKthMinimum stress levels necessaryfor crack growthPhases of crack growthPhase 1Phase 2Phase 3FractureNo crackgrowthThe crack growth changes from initiation to finalfracture in characteristic ways."Paris diagram"Stable crack growthUnstablecrackgrowthCrack length aLoad cycle number NF1F2F3F4>>>2aFFMinimum crack length forcrack growth (threshold)Critical crack length ac,causes unstable crack growth until fracture.Stable crack growth to thecritical crack length ac