Failure Mechanisms

· An important design limit is the case a = t at which the critical crack size for fast fracture equals the wall thickness.
· For cracks smaller than the minimum size for fracture before yield the vessel will plastically deform rather than rupture. Dimension changes of the vessel will indicate over-pressure conditions.
· Cracks larger than the wall thickness will cause the vessel to leak before fast fracture occurs, and leak detection can indicate their presence.
· The introduction of a safety factor reduces the area under the curve in which "safe" operating conditions occur.
· Both K_c and σ_y are material dependent and yield/fracture curves may be used to compare competing materials.