The effect of specimen geometry on short-crack growth behaviour of a nickel-based superalloy

Short fatigue crack growth behavior in a nickel-based superalloy has been investigated in five different specimen geometries: tension, three-point bend, four-point bend (span/width ratio of 1.0), four-point bend (span/width ratio of 2.5) and torsion. Testing was conducted under equivalent shear strain conditions and growth was monitored using a surface replication technique. The frequency distribution of the number of cycles to a given crack length was determined in the domain 12 microns less than crack length less than 200 microns, enabling a statistical comparison of the data. A one way analysis of variance of the grouped and paired data sets revealed that the three-point bend geometry yielded data inconsistent with the other geometries. It is suggested that the most suitable specimen for short-crack growth fatigue tests is the tension geometry.