Volume 2, Issue 4 (April 2005)
Analysis of Roughness-Induced Crack-Tip Shielding in Terms of Size Ratio Effect
A new theoretical concept is introduced to describe the roughness-induced shielding effects in metallic materials. It is based on the statistics of the local ratio between the characteristic microstructure distance and the plastic zone size. Both the crack branching and the crack closure phenomena are generally described in the frame of linear elastic fracture mechanics under the assumption of the remote Mode I loading. Using this approach, intrinsic values of fracture toughness and fatigue crack growth threshold can be determined, and the roughness-induced component can be separated from other closure components, such as plasticity or oxide induced closure. In order to estimate the total RIS effect, standard material data as the yield stress, the mean grain size, the surface roughness, and the fracture mode are only necessary. Application examples concerning static fracture and fatigue are presented for UHSLA steels, ARMCO iron, aluminum, and titanium alloys.