Buckling analysis and optimization of blade stiffened variable stiffness panels

A rapid and robust semi-analytical model is developed based on the Rayleigh-Ritz energy method for the buckling analysis of blade stiffened variable stiffness panels. The method includes the often neglected, yet important, stiffener ange in the analysis by not only accounting for the local increase in stiffness but, for the first time in a Rayleigh-Ritz method, allowing the structure to respond in a discontinuous manner at the location of the stiffness discontinuity. This is achieved by discretizing the panel at locations of discontinuities such as ange edges and assigning each region individual shape functions thus preventing a global C1-continuous response in the buckled mode shape. The model is shown to be in excellent agreement with, and computationally efficient when compared to, a commercial FEA package. The model is then used in a genetic algorithm optimization study to design blade stiffened variables stiffness panels by applying practical design and failure constraints. Results are compared with optimized conventional stiffened panels and for the case considered, mass savings over 6% are shown to be achievable when utilising variable stiffness laminates as the skin on stiffened panels.