Toward a probabilistic preliminary design criterion for buckling critical composite shells

A probability-based analysis method for predicting buckling loads of 6ompression-loaded laminated composite shells is presented, and its potential as a basis for anew shell-stability-design criterion is demonstrated and discussed. In particular, a database containing information about specimen geometry, material properties; and measured initial geometric imperfections for a selected-group of laminated-composite cylindrical shells is used to calculate new buckling-load "knockdown factors: These knockdown factors ire, shown to be substantially-improved and hence much less conservative than the corresponding deterministic knockdown factors that are presently used by industry. The probability integral associated with the analysis is evaluated by using two methods; that is, by using the exact Monte Carlo method and by using an approximate first-order second-moment method. A comparison. of the results from these two methods indicates that the first-order second-moment method yields results that are conservative for the shells considered. Furthermore the results show that the improved; reliability-based knockdown factor presented always yields a safe estimate of the buckling load for the shells examined.