High-stress fatigue crack propagation in thin AA2024-T3 sheet material

Fatigue crack growth in 1.6-mm-thick sheets of aluminium alloy AA2024-T3 was investigated under very high-stress conditions using 950-mm-wide middle tension (MT) specimens. Experiments were conducted by applying uniaxial load ratiosR(0.1, 0.3 and 0.5) with the maximum nominal stress of 120 MPa following conditions relevant for aircraft fuselage structures. The experiments were conducted with digital image correlation to determine loading conditions acting on the crack tip. Stable crack growth rates of up to da/dN> 4 mm/cycle and Delta K> 100 MPa root m were reached, and final crack lengths 2a> 500 mm were obtained. High-stress intensity factors cause plastic zone sizes that extend up to approximately 100 mm from the crack tip. The da/dN-Delta Kdata obtained in this study provide crucial information about the fatigue crack growth and damage tolerance of very long cracks under high-stress conditions in thin lightweight structures.