FATIGUE CHARACTERISTICS OF CAST-IRON

Fatigue results from cyclic or alternating loading with the fracture d eveloping as a result of crack initiation and growth. For a crack to p ropagate, it is necessary for the crack to open and for the stresses a t the crack tip to exceed the tensile stress of the material. If the t ensile stresses at the crack tip are not present or are below a critic al value, the crack will not propagate. Cast iron was tested under fat igue loading where the stresses were mainly in the compressive region. The lack of tensile stresses increased the range and combination of l oading necessary to induce fatigue failure. A Goodman diagram for desi gn purposes was developed. This diagram can be generated from data obt ained from simple tension, compression, and rotating-beam fatigue test s. The results of these tests actually indicate a significantly larger region for safe design recommendations.