A normalized area-compliance method for monitoring surface crack development in a cylindrical rod

A Normalized Area-compliance method has been shown to be able to predict the depth of an elliptical surface crack in a cylindrical rod. The method involves a combination of optical surface crack length measurement and specimen compliance measurement. Finite element analysis was employed to show that the specimen compliance has a one-to-one correspondence with the Normalized Area (NA) or Normalized Harmonic Mean Radius (NHMR) independent of crack depth and crack aspect ratio and with the crack shape and specimen dimension for a range of crack and specimen dimensions. Based on the finite element analysis, master curves of Normalized Compliance versus Normalized Area have been generated for surface-cracked rod under tension with ends free or constrained from rotation. The accuracy of crack depth prediction using this method has been verified by fractography of fatigue cracked rods. Moreover, fatigue crack growth behaviour deduced from this crack depth measurement agrees well with the crack growth data obtained from the standard compact tension specimen.