In the present work, a series of unstiffened, thinwalled (radius to thickness ratio, R/t -216), metallic cylindrical shells, containing centralized cracks at angles to the shell generators ranging from 0° to 90° at intervals of 15° and of two crack lengths, are internally pressurized in order to determine the effect of crack angle on the failure mechanism of the shells. This is done under two different sets of boundary conditions. In the first case the shell is free to move in the axial

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... n, in the second case this axial movement is constrained. Curves of the maximum pressure leading to global failure of the shells as a function of crack angle for two different crack lengths and for both cases of boundaray consitions are presented. The present experimental data can be used to find a governing predictive crack growth criterion as a function of crack angle. This criterion can be used in commercial finite element codes for predicting the failure of more complex shell structures like those used in transport fuselage shell structures. The experimental data are explained via a fracture mechanics based analysis. For cracks which are inclined with respect to the applied stress, both the opening (tensile) mode I stress intensity factor and the sliding (shear) mode II stress intensity factor are significant. These depend on the angle of the crack with respect to the applied load. Fairly good agreement between analysis and experiment is obtained if adjusted values of Kj c and KH C are used along with the assumption that crack growth is governed by a quadratic failure criterion. The adjusted values account for shell curva-* Graduate student and Professor of Aerospace Engineering respectively, University of Michigan. Assoc. Fellow AIAA, Copyright ture through a bulging factor ft. Finite element simulations of selected shell configurations are carried out to obtain the crack flange deflection corresponding to the burst pressures. An approximate analysis of 0° angle cracks based on technical beam theory and axisymmetric cylindrical shell analysis was presented earlier [1] . Results from this analysis are compared with the present finite element analysis for 0° angle cracks in a forthcoming paper [2] . Finally, images of the crack propagation event acquired at high framing rates for selected shell configurations are included.