controllability-of-cracks-by-stress-gradientThe tensile stress gradient determines the"controllability" of a crack.Turbine diskSteep gradient todecreasing tensilestressFlat gradientHub crack:Uncontrollable crack(cannot be caught)Annulus crack:Controllable crack(can be caught) Cracks that are tolerated in handbooks or inspection specifications, or those that result inparts being scrapped during overhauls, must be contollable!Compressive forceCracking in thenotch cannotcompletely separate thecross-sectionNotched specimenAn example of aunique caseCrack initiationlengthLoad changes, life spanCrack lengthFractureCrack growth diagramAnnulus crack:Controllable crack(can be caught)Steep gradient todecreasing tensilestress