Coalescence and growth of two coplanar short cracks in AA7050-T7451 aluminium alloys

• Specimens with two coplanar short surface cracks tested under fatigue loading.
• Interaction between short cracks had no significant effects on growth rates.
• Crack growth rate deceleration in the surface direction observed at coalescence.
• Deceleration appear necessary for a larger semi-elliptical shaped crack to form.
• An improved method which accounts for this ‘deceleration’ period is developed.

Quantitative fractography was used to study fatigue test specimens (AA7050-T7451) with short surface cracks to determine their interaction and coalescence. Methods for predicting the coalescence of cracks described by ASME, BSI PD6493 and Iida were compared with the present experimental results. An improved method was developed to predict the coalescence of two coplanar short cracks and subsequent growth as a single larger crack by including a period of crack growth deceleration at the point of coalescence as observed in the present experiments, which appeared to be associated with the development of a single, larger semi-elliptical shaped crack (i.e. a coalesced crack).