Crack Initiation and Propagation

 

Stageifatigue failure:

 

I. cracinitiation at high stress point(stress raisers) II. propagation (incrementaieaccycle)

III. finafailure by fracture

 

Stage I - propagation

 

•   slow

 

•   along crystallographic planes of high shear stress

 

•   flaand featureless fatigue surface

 

 

Stage II - propagation

 

Crack propagateby repetitive plastic blunting and sharpening of the cractip.