Prediction of fatigue life in aluminium alloy (AA7050-T7451) structures in the presence of multiple artificial short cracks

• The growth and coalescence of multiple artificial short cracks in aluminium alloy AA7050-T451 were studied.
• Accuracy of existing theoretical methods for predicting the growth and coalescence of multiple cracks was evaluated.
• A larger crack can grow with very little influence from smaller coplanar cracks.
• Crack growth retardation period offsets increase in crack length when cracks coalesce.
• Fatigue life is largely dominated by the growth of the largest crack.

Although methods for predicting the growth and coalescence of cracks have been introduced, uncertainties persist in structures with multiple short cracks. Quantitative fractographic methods were used to study the way in which multiple short cracks in AA7050-T7451 of varying sizes on the same and on different planes grew under low amplitude cyclic loading. The accuracy of existing theoretical methods for predicting the growth and coalescence of multiple cracks was evaluated. Experimental results corroborate the findings that growth of the ‘largest’ crack dominated the fatigue life of a specimen with very little influence from relatively shorter cracks.