The growth of part-through cracks from surface notches is investigated using artificially marked fracture surfaces of both fatigued and monotonically loaded specimens. Experimental results for all specimen and crack geometries considered show that erroneous estimates of the growth of part-through cracks in thick-walled metal specimens are obtained when calculated on the basis of the stress intensity factor distribution along the crack front and on an assumed uniform response of the material throughout the specimen volume.

It is suggested that these discrepancies can be explained by a stress state dependent mechanical response of the material at the front of the loaded crack. Using this idea, qualitative models are proposed which account for the experimentally observed tendencies in the crack shape development as well as the influence of the load level on them. The effects of specimen size and bending constraint of the specimen also are discussed within the framework of the experimental results.