Residual strength of cracked stiffened panels

Abstract

In this report a method for the prediction of the residual strength of cracked stiffened panels, presented in an earlier NLR publication, is further evaluated. The method takes full account of sheet-stringer interaction in the cracked region and sets a criterion for unstable crack growth arrest. Ultimate panel failure is then initiated either by subsequent unstable crack growth or by stiffener failure. Critical load conditions for both failure modes are presented determining a safe load level for cracks to be stopped. In cases where crack arrest does not occur, the residual strength level of the unstiffened panel constitutes a safe lower bound. The results of residual strength tests on bonded and riveted panels with symmetric strip stiffeners or eccentric Z-stringers substantiate the residual strength hypothesis. Finally results of computed stress distributions and interacting rivet forces are presented and the essential stiffener properties to be included in a design analysis are indicated.