The stable tearing behavior of thin sheets of 2024-T3 aluminum alloy was investigated for middle crack tension, M(T), and compact tension, C(T), specimens. The surface crack-tip opening angle (CTOA), applied loads, crack extension, and local displacements were measured. A critical CTOA fracture criterion was incorporated into a two-dimensional, elastic-plastic finite element code and used to simulate the experimental fracture behavior.
The CTOA measurements and observations of the fracture surfaces have shown that (a) large values for surface CTOA were observed for small crack extensions (less than the sheet thickness), (b) substantial tunneling of the crack was associated with small crack extensions, (c) crack tunneling in the M(T) specimen was less than that observed in the C(T) configuration, (d) for larger crack extensions, the measured CTOA values were determined to be approximately 6‡ for both the M(T) and C(T) configuration, and (e) for larger crack extensions, crack tunneling was small and remained constant.
The two-dimensional finite element predictions of fracture behavior assumed a constant critical CTOA value of 6‡ and accounted for local crack tip constraint with a plane strain core of elements ahead of the crack tip. The plane strain core extended 2.5mm above and below the crack plane. The simulations were within ±4% of the maximum applied load for the C(T) tests and within 2% for the M(T) tests.