Axial crack propagation and arrest in pressurized fuselage

A hybrid experimental-numerical investigation was undertaken to establish a practical crack kinking criterion in the presence or absence of multiple site damage (MSD) in a pressurized airplane fuselage. Ramulu-Kobayashi crack kinking criteria was modified to predict self-similar crack propagation along a line of MSD and subsequent kinking near a tear strap. Instrumented biaxial test specimens and small-scale fuselage rupture experiments were conducted to generate the crack kinking and crack velocity data which was then input to a large deformation, elasto-dynamic, finite element model of the fracture specimen. The computed mixed mode I and II stress intensity factors and a large axial stress preceding the propagating crack were used to evaluate the self-similar crack extension and the crack kinking criterion along the crack trajectory. Excellent agreement was obtained between the predicted and measured crack kinking angles and locations. Additional verification was made through the match between the computed and measured strain gage data.; The biaxial specimen tests showed that in spite of the presence of K{dollar}sb{lcub}rm II{rcub}{dollar} and the large axial stress ahead of the propagating crack, axial crack extension would continue in the axial direction if the skin is weakened by MSD. The crack propagated through the tear strap in the presence of a continuous MSD and kinked when the MSD terminated at the tear strap.; The small-scale fuselage rupture tests showed that the pre-existing axial through crack along the stringer immediately kinked upon propagation due to the mixed modes I and II state caused by the one-sided opening of the crack flap. The diagonally running crack subsequently turned circumferentially along the tear straps or the two cylinder ends. Again the experimented results were used to execute an elasto-dynamic finite element analysis to verify crack kinking and self-similar crack extension in the presence of the mixed mode state along the stringer and final crack curving at the tear strap.