SEDL / STP / STP536-EB / STP49650S

Plane-Stress Fracture Toughness and Fatigue-Crack Propagation of Aluminum Alloy Wide Panels

Wang, D. Y.
Senior engineer, McDonnell Douglas Corp., Long Beach, Calif.

Pages: 16    Published: Jan 1973

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Abstract

The effects of panel width and crack length on fracture toughness and the fatigue crack propagation rate of Alclad 2024-T3 and X7475 were investigated in sheet specimens ranging from 30 to 120 in. wide. The unstiffened, wide panels containing a through-the-thickness central crack were tested under uniaxial loadings to generate fatigue crack growth, stable crack growth, and residual strength data. In addition, 48-in. wide 7075-T6 and 7079-T6 aluminum alloy panels were tested at −65° F to determine low-temperature effects. The analysis was conducted to define the parameters contributing to the apparent panel size effects and to outline the procedures to obtain valid data applicable to full-scale structural design. Excellent correlation was found in the stable crack growth resistance curve (KR versus Δa) data obtained from panels of various width which contained initial crack lengths ranging from 3.6 to 30 in. The results suggest that the crack growth resistance curve is a material parameter which is independent of crack length and panel width under an appropriate test condition. The effects of −65° F significantly reduce fatigue crack propagation resistance at a relatively high ΔK level and stable static crack growth resistance of some aluminum alloy sheets.