CRACK-TIP BEHAVIORS OF STATIONARY AND GROWING CRACKS IN AL-FE-X ALLOYS .1. NEAR-TIP STRAIN FIELD

The crack-tip strain fields of monotonically loaded stationary and growing cracks in Al-Fe-X alloys have been examined using the stereoimaging technique. The experimental results confirm the dominance of the Hutchinson[10,11] and Rice and Rosengren[12] (HRR) field in a stationary crack and the logarithmic singularity in a nonstationary crack. Initiation of fracture is preceded by the formation of localized shear bands emitted from the crack tip. The dominance of the HRR or the logarithmic field ceases to exist within the fracture process zone, whose size is related to the crack-tip opening displacement and the limit effective strain prior to shear localization. In all cases, the value of the limit effective strain outside the shear bands approximately equals the fracture strain measured in a tensile specimen. These observations are used to establish the origin of stable crack growth and a local fracture criterion. © 1990 The Metallurgical of Society of AIME.