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A method, based on displacement compatibility, is presented for the fracture analysis of cracked stiffened structure. The method provides an economical means for the determination of crack-tip stress intensity factors and stiffener stress concentration factors that can be used for parametric crack growth and residual strength studies during the initial design phase of an aircraft structure. The results of a typical parametric study are included. Emphasis is placed on the need to account for stiffener bending stresses in residual strength calculations. This need is supported by test evidence. Fastener shear failure known as unzipping is discussed. An example, supported by test evidence, is shown where this phenomenon can precipitate failure of stiffened structure containing cracks. A method of analysis, based on fastener nonlinear shear displacements, is described, which can account for the effect of fastener failure during the failure process of a cracked stiffened panel. The method is verified by test.
cracks, fracture (materials), crack propagation, damage tolerance, cracked stiffened structure, fracture mechanics, residual strength
National resource specialist, Fracture Mechanics Metallurgy, Federal Aviation Administration, Long Beach, CA