Fracture Modes and Mechanisms

Breaking bonds of any type is the fundamental precursor to crack nucleation. Catastrophic brittle or cleavage fracture produces essentially only cleavage steps, while variations in ductile fracture produce different sizes of cup-cone (ductile-dimple) fracture surface structures. Steels in particular are prone to low-temperature ductile – brittle transitions while variations or cycles in stress produce fatigue structures and behavior. Fracture induced by creep, fatigue, creep-fatigue, impact, as well as ductile/brittle fracture modes are illustrated. Crack nucleation, coalescence, and growth are described in detail along with crack initiation sites corresponding to the various fracture modes. Complex interactions of fracture modes in various stress, temperature, and chemical environments are illustrated.